Ahmed, N., Shamsabadi, A., Chudasama, V.*
ACS Omega, 2020, Advance Article.
Herein, we report the transformation of readily accessed acyl hydrazides into protected 2-aminobenzophenones via a two-step process involving an aryne-based molecular rearrangement followed by a one-pot addition–elimination procedure. The assembly of the scaffold is tolerant of a wide variety of functional groups, and the carbamate group on the product can be facilely removed to afford highly valuable 2-aminobenzophenones. Application of the protocol was demonstrated in the synthesis of neurological medicine phenazepam.
Fernandez, M., Shamsabadi, A., Chudasama, V.*
Chem Commun, 2020, Advance Article.
Herein we report the synthesis of a library of thioalkyl- and thioaryl-pyridazinediones for thiol-based self-immolative release of cargo. A bisthioaryl-pyridazinedione is shown to be stable to serum protein albumin but unstable in intracellular conditions. A derivatised analogue underwent self-immolative degradation in cellular thiol conditions as evidenced by LC-MS/release of a turn-on fluorescence fluorophore; versatility of the thiol-pyridazinedione is demonstrated through synthesis of SMDC precursors that contain three different functional groups on the same central molecule.
Bahou, C.,^ Spears, R. J.,^ Aliev, A. E., Maruani, A., Fernandez, M., Javaid, F., Szijj, P. A., Baker, J. R., Chudasama, V.* (^ joint 1st authors)
Chem Commun, 2019, 55, 14829-14832.
Herein we report a retro-Michael deconjugation pathway of thiol–pyridazinedione linked protein bioconjugates to provide a novel cleavable linker technology. We demonstrate that the novel pyridazinedione linker does not suffer from off-target modification with blood thiols (e.g., glutathione, human serum albumin (HSA)), which is in sharp contrast to an analogous maleimide linker.
Atkinson, B. N., Chudasama, V., Browne, L. E.
Purinergic Signaling, 2019, pp 301-309.
This chapter details methods to express and modify ATP-gated P2X receptor channels so that they can be controlled using light. Following expression in cells, a photoswitchable tool compound can be used to covalently modify mutant P2X receptors, as previously demonstrated for homomeric P2X2 and P2X3 receptors, and heteromeric P2X2/3 receptors. Engineered P2X receptors can be rapidly and reversibly opened and closed by different wavelengths of light. Light-activated P2X receptors can be mutated further to impart ATP-insensitivity if required. This method offers control of specific P2X receptor channels with high spatiotemporal precision to study their roles in physiology and pathophysiology.
Forte, N., Benni, I., Karu, K., Chudasama, V.*, Baker, J. R.
Chem Sci, 2019, 10, 10919-10924.
The modification of lysine residues with acylating agents has represented a ubiquitous approach to the construction of antibody conjugates, with the resulting amide bonds being robustly stable and clinically validated. However, the conjugates are highly heterogeneous, due to the presence of numerous lysines on the surface of the protein, and greater control of the sites of conjugation are keenly sought. Here we present a novel approach to achieve the targeted modification of lysines distal to an antibody fragment’s binding site, using a disulfide bond as a temporary ‘hook’ to deliver the acylating agent. This cysteine-to-lysine transfer (CLT) methodology offers greatly improved homogeneity of lysine conjugates, whilst retaining the advantages offered by the formation of amide linkages.
Wall, A., Nicholls, K., Caspersen, M.,Skrivergaard, S., Howard, K.A., Karu, K., Chudasama, V.*, Baker, J.R.
Org Biomol Chem, 2019, 17, 7870-7873.
Conjugation of therapeutics to human serum albumin (HSA) using bromomaleimides represents a promising platform for half-life extension. We show here that the Cys-34 crevice substantially reduces the rate of serum stabilising maleimide hydrolysis in these conjugates, necessitating reagent optimisation. This improved reagent design is applied to the construction of an HSA-paclitaxel conjugate, preventing drug loss during maleimide hydrolysis.
Forte, N., Morais, M., Chudasama, V., Baker, J.R.
Bioconjugation. Methods in Molecular Biology, vol 2033. Humana, New York, NY, pp 15-24.
Site-selective antibody conjugation is widely recognized as a key strategy for the optimum construction of antibody–drug conjugates (ADCs). Achieving such bioconjugation directly onto native antibodies would represent the ideal solution, as it would afford greatly improved homogeneity whilst avoiding the need for genetic engineering, and even allow the repurposing of existing antibodies “off-the shelf.” Here we describe a protocol for the use of next-generation maleimides (NGMs) for the selective modification of the four interchain disulfide bonds present in a typical IgG1 antibody format. These reagents retain the efficiency of classical maleimides whilst serving to rebridge each reduced disulfide bond, affording one attachment per disulfide. The approach is simple, uses readily available reagents, and generates robustly stable conjugates which are ideal for in vitro or in vivo applications. In addition to use in the construction of ADCs these reagents can also be used to develop antibody conjugates for imaging, bispecifics, and broadly for use across biology and medicine.
Nogueira, J., Greene, M., Richards, D. A., Furby, A. O., Steven, J., Porter, A., Barelle, C., Scott, C. J., Chudasama, V.*
Chem Commun, 2019, 55, 7671-7674.
Herein we report the construction of a nanoparticle-based drug delivery system which targets a key regulator in tumour angiogenesis. We exploit a Variable New Antigen Receptor (VNAR) domain, conjugated using site-specific chemistry, to direct PLGA-PEG nanoparticles to DLL4. The importance of site-specific chemistry for achieving high avidity in these systems is demonstrated.
Bahou, C., Love, E., Leonard, S., Spears, R. J., Maruani, A., Armour, K., Baker, J. R., Chudasama, V.*
Bioconjugate Chem, 2019, 30, 1048-1054.
Modification of immunoglobulin G (IgG) 1 proteins in cancer treatment is a rapidly growing field of research. Antibody–drug conjugates (ADCs) exploit the targeted nature of this immunotherapy by conjugating highly potent drugs to antibodies, allowing for effective transport of cargo(s) to cancerous cells. Of the many bioconjugation strategies now available for the formation of highly homogenous ADCs, disulfide modification is considered an effective, low-cost and widely accepted method for modifying IgG1s for improved clinical benefit. However, little is known about how disulfide modification impacts clinically relevant fragment crystallisable (Fc) region interactions. Although often overlooked as a secondary ADC function, Fc interactions could prove key in rational design of cancer cell-targeting ADCs through consideration of potent mechanisms such as antibody-dependant cellular cytotoxicity (ADCC). This work explores different IgG1 disulfide modification techniques and the effect they have on quantifiable secondary IgG1 Fc interactions (e.g. CD16a and FcRn). The solvent accessible disulfide residues of trastuzumab, a clinically relevant IgG1, were modified to provide a range of bioconjugates with differing amounts of inter-chain covalent linkages. It was found that by natively re-bridging the IgG1 model, all tested Fc functionalities were not significantly affected. Additionally, in non Fc-specific biophysical experiments (e.g. thermal stability/aggregation), the natively re-bridged species provided an exceptional profile, showing no significant change from the tested native antibody. Conjugates with significant disruption of the covalent connectivity of IgG1 chains resulted in a suboptimal Fc profile (CD16a kinetics or ADCC activity), in addition to sub-standard non Fc-specific attributes (thermal stability). These results advocate native disulfide re-bridging as an excellent synthetic strategy for forming homogenous IgG1 bioconjugates, with no reported negative impact on biophysical profile relative to the native antibody.
Shamsabadi, A., Chudasama, V.*
Org Biomol Chem, 2019, 17, 2865-2872.
Herein we describe recent developments in selective, metal-free, dioxygen-induced C–H activation. This method of activating C–H bonds is an attractive alternative to traditional methodologies as it uses dioxygen, an inherently sustainable and widely accessible oxidant, in place of expensive or toxic metals and/or hazardous peroxides. Reactions developed on the basis of using aerobic C–H activation are also discussed.
Galan, S. R. G., Wickens, J. R., Dadova, J., Ng, W.-L., Zhang, X., Simion, R. A., Quinlan, R., Pires, E., Paton, R. S., Caddick, S., Chudasama, V.*, Davis, B. G.
Nature Chem Bio, 2018, 14, 955-963.
Isotopic replacement has long-proven applications in small molecules. However, applications in proteins are largely limited to biosynthetic strategies or exchangeable (for example, N–H/D) labile sites only. The development of postbiosynthetic, C–1H → C–2H/D replacement in proteins could enable probing of mechanisms, among other uses. Here we describe a chemical method for selective protein α-carbon deuteration (proceeding from Cys to dehydroalanine (Dha) to deutero-Cys) allowing overall 1H→2H/D exchange at a nonexchangeable backbone site. It is used here to probe mechanisms of reactions used in protein bioconjugation. This analysis suggests, together with quantum mechanical calculations, stepwise deprotonations via on-protein carbanions and unexpected sulfonium ylides in the conversion of Cys to Dha, consistent with a ‘carba-Swern’ mechanism. The ready application on existing, intact protein constructs (without specialized culture or genetic methods) suggests this C–D labeling strategy as a possible tool in protein mechanism, structure, biotechnology and medicine.
Drug Discov Today Technol., 2018, 30, 1-2.
Forte, N., Chudasama, V.*, Baker J. R.
Drug Discov Today Technol., 2018, 30, 11-20.
Antibody-drug conjugates (ADCs) constructed using site-selective labelling methodologies are likely to dominate the next generation of these targeted therapeutics. To this end, disulfide bridging has emerged as a leading strategy as it allows the production of highly homogeneous ADCs without the need for antibody engineering. It consists of targeting reduced interchain disulfide bonds with reagents which reconnect the resultant pairs of cysteine residues, whilst simultaneously attaching drugs. The 3 main reagent classes which have been exemplified for the construction of ADCs by disulfide bridging will be discussed in this review; bissulfones, next generation maleimides and pyridazinediones, along with others in development.
Shamsabadi, A., Chudasama, V.*
Chem Commun, 2018, 54, 11180-11183.
Herein we report the transformation of readily synthesised/facilely accessed acyl hydrazides into 2-hydrazobenzophenones via a novel molecular rearrangement using aryne chemistry. The developed reaction protocol is performed under relatively mild conditions, is tolerant of a wide variety of functional groups, and the 2-hydrazobenzophenone products provide access to both 1H– and 2H-indazoles from a single intermediate.
Szijj, P. A., Bahou, C., Chudasama, V.*
Drug Discov. Today Technol., 2018, 30, 27-34.
Bioconjugation, the modification of biological macromolecules such as proteins, is an up and coming area in the field of chemical biology. Antibody-drug conjugates (ADCs), combining the antigen-selectivity of natural antibodies with the cytotoxic potency of small molecule drugs, are a powerful therapeutic technology. Four such constructs are currently on the market for cancer therapy. However, the conjugation methodology employed in these therapeutics is far from ideal. Herein we provide an overview on methods that attempt to increase the safety and efficacy of ADCs via “self-hydrolysing maleimides” or by improving the stability of maleimide-conjugates by other means. We find that some very promising reagents have been reported, however the mechanism by which each of these reagents acts is not clear, thus limiting rational design for some strategies.
Forte, N., Livanos, M., Miranda, E., Morais, M., Yang, X., Rajkumar, V.S., Chester, K.A.,Chudasama, V.*, Baker, J.R.
Bioconjugate Chem, 2018, 29, 486-492.
We describe investigations to expand the scope of next generation maleimide cross-linkers for the construction of homogeneous protein–protein conjugates. Diiodomaleimides are shown to offer the ideal properties of rapid bioconjugation with reduced hydrolysis, allowing the cross-linking of even sterically hindered systems. The optimized linkers are exploited to link human serum albumin to antibody fragments (Fab or scFv) as a prospective half-life extension platform, with retention of antigen binding and robust serum stability. Finally, a triprotein conjugate is formed, by linking scFv antibody fragments targeting carcinoembryonic antigen. This tri-scFv is shown to infer a combination of greater antigen avidity and increased in vivo half-life, representing a promising platform for antibody therapeutic development.
Bahou, C., Richards, D.A., Maruani, A., Love, E.A., Javaid, F., Caddick,S., Baker, J.R, Chudasama, V.*
Org Biomol Chem, 2018, 16, 1359-1366.
Due to their exquisite cysteine-selectivity, excellent stability, and ability to functionally rebridge disulfide bonds, dibromopyridazinediones are emerging as an exciting new class of bioconjugation reagents, particularly in the field of antibody conjugation. Despite this, relatively little work has been performed on the optimisation of their synthesis and subsequent reaction with immunoglobulins. Herein we present a novel synthetic route towards functionalised dibromopyridazinediones, proceeding via an isolatable dibromopyridazinedione-NHS ester. Reaction of this activated intermediate with a variety of amines produces functional dibromopyridazinediones in good to excellent yields. The disulfide rebridging capacity of these reagents was optimised on the clinically relevant IgG1 trastuzumab, resulting in a general method which allows for the generation of site-selectively modified native trastuzumab with over 90% homogeneity (no disulfide scrambling) without the need for protein engineering or enzymatic conjugation.
Cheng, M., Maruani, A., Savoie, H., Chudasama, V.*, Boyle, R.W.
Org Biomol Chem, 2018, 16, 1144-1149.
We herein report the synthesis and analysis of a novel aza-BODIPY–antibody conjugate, formed by controlled and regioselective bioconjugation methodology. Employing the clinically relevant antibody, which targets HER2 positive cancers, represents the first example of an antibody targeting strategy for this class of near-IR emitting fluorophore. The NIR fluorescence and binding properties were validated through in vitro studies using live cell confocal imaging.
Fernandez, M., Javaid, F., Chudasama, V.*
Chem Sci, 2018, 9, 790-810.
The folate receptor (FR) is a recognised biomarker for tumour cells due to it being overexpressed on a large number of tumours. Consequently, the FR has been exploited by many diagnostic and therapeutic tools to allow targeted delivery to, and imaging of, cancer cells. Herein, we describe the many different approaches by which this has been achieved, including the attachment of folate to potent chemotherapeutic drugs to form FR-targeting small molecule drug conjugates (SMDCs), FR-targeting antibodies (as antibody alone and as an antibody-drug conjugate), and in the form of complementary nanotechnology-folate platforms; as well as imaging variants thereof. The potential of exploiting the FR for targeted therapy/imaging has the potential to revolutionise the way several cancers are treated. These FR-targeted technologies can also pave the way for inspiring further sophisticated drug conjugates, especially as this receptor is being targeted by use of several complementary technologies: small molecule, nanoparticle and protein-based – thus providing broad and distinct knowledge in the area.
Bryden, F., Maruani, A., Rodrigues, J.M.M., Cheng, M.H.Y., Savoie, H., Beeby, A., Chudasama, V.*, Boyle, R.W.
Bioconjugate Chem, 2018, 29, 176-181.
Exploitation of photosensitisers as payloads for antibody-based anti-cancer therapeutics offers a novel alternative to the small pool of commonly-utilised cytotoxins. However, existing bioconjugation methodologies are incompatible with the requirement of increased antibody loading without compromising antibody function, stability or homogeneity. Herein, we describe the first application of dendritic multiplier groups to allow the loading of more than 4 porphyrins to a full IgG antibody in a site-specific and highly homogeneous manner. Photophysical evaluation of UV-visible absorbance and singlet oxygen quantum yields highlighted porphyrin-dendron 14 as the best candidate for bioconjugation; with subsequent bioconjugation producing a HER2-targeted therapeutic with average loading ratios of 15.4:1. In vitro evaluation of conjugate 18 demonstrated a nanomolar photocytotoxic effect in a target cell line, which overexpresses HER2, with no observed photocytotoxicity at the same concentration in a control cell line which expresses native HER2 levels, or in the absence of irradiation with visible light.
Loynachan, C.N., Thomas, M.R., Gray, E.R., Richards, D.A., Kim, J., Miller, B.S., Brookes, J.C., Agarwal, S., Chudasama, V., McKendry, R.A., Stevens, M.M.
ACS Nano, 2018, 12, 279-288.
Paper-based lateral flow immunoassays (LFIAs) are one of the most widely used point-of-care (PoC) devices, however, their application in early disease diagnostics is often limited due to insufficient sensitivity for the requisite sample sizes and the short timeframes of PoC testing. To address this, we developed a serum-stable, nanoparticle catalyst-labelled LFIA with a sensitivity surpassing that of both current commercial and published sensitivities for paper-based detection of p24, one of the earliest and most conserved biomarkers of HIV. We report the synthesis and characterization of porous platinum core-shell nanocatalysts (PtNCs), which show high catalytic activity when exposed to complex human blood serum samples. We explored the application of antibody functionalized PtNCs with strategically and orthogonally modified nanobodies with high affinity and specificity toward p24 and establish the key larger nanoparticle size regimes needed for efficient amplification and performance in LFIA. Harnessing the catalytic amplification of PtNCs enabled naked-eye detection of p24 spiked into sera in the low femtomolar range (ca. 0.8 pg•mL-1), and the detection of acute phase HIV in clinical human plasma samples in under 20 minutes. This provides a versatile absorbance-based and rapid LFIA with sensitivity capable of significantly reducing the HIV acute phase detection window. This diagnostic may be readily adapted for detection of other biomolecules; as an ultrasensitive screening tool for infectious and non-communicable diseases, and can be capitalized upon in PoC settings for early disease detection.
Greene, M., Richards, D.A., Nogueira, J., Campbell, K., Smyth, P., Fernandez, M., Scott, C.J., Chudasama, V.*
Chem Sci, 2018, 9, 79-87.
The successful development of targeted nanotherapeutics is contingent upon the conjugation of therapeutic nanoparticles to target-specific ligands, with particular emphasis placed on antibody-based ligands. Thus, new methods which enable the covalent and precise installation of targeting antibodies to nanoparticle surfaces are greatly desired, especially those which do not rely on costly and time-consuming antibody engineering techniques. Herein we present a novel method for the highly controlled and oriented covalent conjugation of non-engineered antibody F(ab) fragments to PLGA-PEG nanoparticles using disulfide-selective pyridazinedione linkers and strain-promoted alkyne-azide click chemistry. Exemplification of this method with trastuzumab and cetuximab showed significant improvements in both conjugation efficiency and antigen binding capability, when compared to commonly employed strategies for antibody-nanoparticle construction. This new approach paves the way for the development of antibody-targeted nanomedicines with improved paratope availability, reproducibility and uniformity to enhance both biological activity and ease of manufacture.
Shamsabadi, A., Ren, J., Chudasama, V.*
RSC Adv, 2017, 7, 27608-27611.
Herein we report the one-pot transformation of readily synthesised/easily accessed acyl hydrazides into N-acyl carbamates via an alkylation-elimination reaction sequence. A range of N-acyl carbamates are prepared in consistent yields, including those featuring protecting groups and having alkyl & aryl N-acyl functionality. The reaction conditions also tolerate a wide variety of sensitive functional groups.
Nunes, J.P.M., Vassileva, V., Robinson, E., Morais, M., Smith, M.E.B., Pedley, R. B., Caddick, S., Baker, J.R., Chudasama, V.*
RSC Adv, 2017, 7, 24828-24832.
Herein we demonstrate that conjugation of a next generation maleimide (NGM) to engineered cysteines in a THIOMAB™ antibody delivers a THIOMAB™ antibody-drug conjugate (TDC) with a drug loading of ca. 2. This TDC is highly stable in blood serum conditions, selective and potent towards HER2 expressing cell lines and meets the current criteria for optimised antibody-drug conjugates (ADCs).
Morais, M., Nunes, J.P.M., Karu, K., Forte, N., Benni, I., Smith, M.E.B., Caddick, S., Chudasama, V.*, Baker, J.R.
Org Biomol Chem, 2017, 15, 2947-2952.
Disulfide bridging offers a convenient approach to generate site-selective antibody conjugates from native antibodies. To optimise the reagents available to achieve this strategy, we describe here the use of dibromomaleimides designed to undergo accelerated post-conjugation hydrolysis. Conjugation and hydrolysis, which serve to ‘lock’ the conjugates as robustly stable maleamic acids, is achieved in just over 1 h. This dramatic acceleration is also shown to infer significant improvements in homogeneity, as demonstrated by mass spectrometry analysis.
Robinson E., Nunes, J.P.M., Vassileva V., Maruani, A., Nogueira J.C.F., Smith, M.E.B., Pedley, B., Caddick, S., Baker, J.R., Chudasama, V.*
RSC Adv, 2017, 7, 9073-9077.
Herein we report the use of pyridazinediones to functionalise the native solvent accessible interstrand disulfide bonds in trastuzumab with monomethyl auristatin E (MMAE). This method of conjugation delivers serum stable antibody–drug conjugates (ADCs) with a controlled drug loading of 4. Moreover, we demonstrate that the MMAE-bearing ADCs are potent, selective and efficacious against cancer cell lines in both in vitro and in vivo models.
Lee, M.T.W., Maruani, A., Richards, D.A., Baker, J.R., Caddick, S., Chudasama, V.*
Chem Sci, 2017, 8, 2056-2060.
The generation of antibody conjugates with a loading of two modules is desirable for a host of reasons. Whilst certain antibody engineering approaches have been useful in the preparation of such constructs, a reliable method based on a native antibody scaffold without the use of enzymes or harsh oxidative conditions has hitherto not been achieved. The use of native antibodies has several advantages in terms of cost, practicality, accessibility, time and overall efficiency. Herein we present a novel, reliable method of furnishing antibody conjugates with a loading of two modules starting from a native antibody scaffold.
45. An overview of the synthesis of acyl hydrazides from aldehydes and reactions of the products thereof
Shamsabadi, A. and Chudasama, V.*
Org Biomol Chem, 2017, 15, 17-33.
Herein a review on the methods for the formation and reaction of acyl hydrazides will be given. There is particular focus on the synthesis of acyl hydrazides from aldehyde precursors with examination of the various approaches (e.g. metal-based (rhodium, copper) and non-metal-based (aerobically- and photoorganocatalytically-initiated)) that have been used to achieve this. Finally, strategies to utilise acyl hydrazides for the formation of an array of useful entities will be detailed.
Richards, D. A., Maruani, A. and Chudasama, V.*
Chem Sci, 2017, 8, 63-77.
Recent advances in nanomedicine have shown that dramatic improvements in nanoparticle therapeutics and diagnostics can be achieved through the use of disease specific targeting ligands. Although immunoglobulins have successfully been employed for the generation of actively targeted nanoparticles, their use is often hampered by the suboptimal characteristics of the resulting complexes. Emerging data suggest that a switch in focus from full antibodies to antibody derived fragments could help to alleviate these problems and expand the potential of antibody–nanoparticle conjugates as biomedical tools. This review aims to highlight how antibody derived fragments have been utilised to overcome both fundamental and practical issues encountered during the design and application of antibody–targeted nanoparticles.
Smoktunowicz, N., Platé, M., Stern, A. O., D’Antongiovanni, V., Robinson, E., Chudasama, V., Caddick, S., Scotton, C. J., Jarai G. and Chambers, R. C.
Oncotarget, 2016, 7, 65471-65484.Abstract
The major high-affinity thrombin receptor, proteinase activated receptor-1 (PAR-1) is expressed at low levels by the normal epithelium but is upregulated in many types of cancer, including lung cancer. The thrombin-PAR-1 signalling axis contributes to the activation of latent TGFβ in response to tissue injury via an αvβ6 integrin-mediated mechanism. TGFβ is a pleiotropic cytokine that acts as a tumour suppressor in normal and dysplastic cells but switches into a tumour promoter in advanced tumours. In this study we demonstrate that TGFβ is a positive regulator of PAR-1 expression in A549 lung adenocarcinoma cells, which in turn increases the sensitivity of these cells to thrombin signalling. We further demonstrate that this effect is Smad3-, ERK1/2- and Sp1-dependent. We also show that TGFβ-mediated PAR-1 upregulation is accompanied by increased expression of integrin αv and β6 subunits. Finally, TGFβ pre-stimulation promotes increased migratory potential of A549 to thrombin. These data have important implications for our understanding of the interplay between coagulation and TGFβ signalling responses in lung cancer.
Pye, H., Butt M.A., Reinert, H.W., Maruani, A., Nunes, J.P.M., Marklew, J.S., Qurashi, M., Funnell, L., May, A., Stamati, I., Hamoudi, R., Baker, J.R., Smith, M.E.B., Caddick, S., Deonarain, M., Yahioglu, G., Chudasama, V.*, Lovat, L.
Photochem Photobiol Sci, 2016, 15, 1227-1238.Abstract
In many cancers early intervention involves surgical resection of small localised tumour masses. Inadequate resection leads to recurrence whereas overzealous treatment can lead to organ damage. This work describes production of a HER2 targeting antibody Fab fragment dual conjugated to achieve both real time near-infrared fluorescent imaging and photodynamic therapy. The use of fluorescence emission from a NIR-dye could be used to guide resection of tumour bulk, for example during endoscopic diagnosis for oesophago-gastric adenocarcinoma, this would then be followed by activation of the photodynamic therapeutic agent to destroy untreated localised areas of cancer infiltration and tumour infiltrated lymph nodes. This theranostic agent was prepared from the Fab fragment of trastuzumab initially by functional disulfide re-bridging and site-specific click reaction of a NIR-dye. This was followed by further reaction with a novel pre-activated form of the photosensitiser chlorin e6 with the exposed fragments’ lysine residues. Specific binding of the theranostic agent was observed in vitro with a HER2 positive cell line and cellular near-infrared fluorescence was observed with flow cytometry. Specific photo-activity of the conjugates when exposed to laser light was observed with HER2 positive but not HER2 negative cell lines in vitro, this selectivity was not seen with the unconjugated drug. This theranostic agent demonstrates that two different photo-active functions can be coupled to the same antibody fragment with little interference to their independent activities.
Maruani, A., Richards, D.A., Chudasama, V.*
Org Biomol Chem, 2016, 14, 6165-6178.Abstract
With the advent of novel bioorthogonal reactions and “click” chemistry, an increasing number of strategies for the single labelling of proteins and oligonucleotides have emerged. Whilst several methods exist for the site-selective introduction of a single chemical moiety, site-selective and bioorthogonal dual modification of biomolecules remains a challenge. The introduction of multiple modules enables a plethora of permutations and combinations and can generate a variety of bioconjuguates with many potential applications. From de novo approaches on oligomers to the post-translational functionalisation of proteins, this review will highlight the main strategies to dually modify biomolecules.
Chudasama, V.*, Maruani, A., Caddick, S.
Nature Chem, 2016, 8, 114-119.
Antibody–drug conjugates (ADCs) comprise antibodies covalently attached to highly potent drugs using a variety of conjugation technologies. As therapeutics, they combine the exquisite specificity of antibodies, enabling discrimination between healthy and diseased tissue, with the cell-killing ability of cytotoxic drugs. This powerful and exciting class of targeted therapy has shown considerable promise in the treatment of various cancers with two US Food and Drug Administration approved ADCs currently on the market (Adcetris and Kadcyla) and approximately 40 currently undergoing clinical evaluation. However, most of these ADCs exist as heterogeneous mixtures, which can result in a narrow therapeutic window and have major pharmacokinetic implications. In order for ADCs to deliver their full potential, sophisticated site-specific conjugation technologies to connect the drug to the antibody are vital. This Perspective discusses the strategies currently used for the site-specific construction of ADCs and appraises their merits and disadvantages.
Lee, M.T.W., Maruani, A., Baker, J.R., Caddick, S., Chudasama, V.*
Chem Sci, 2016, 7, 799-802.
Herein we present a significant step towards next-generation disulfide stapling reagents. A novel class of reagent has been designed to effect both disulfide reduction and functional re-bridging. The strategy has been applied to great success across various peptides and proteins. Moreover, application to a multi-disulfide system resulted in functional re-bridging without disulfide scrambling.
Gaitzsch, J., Chudasama, V.*, Morecroft, E., Messager, L., Battaglia, G.
ACS Macro Lett, 2016, 5, 351-354.
Herein we report the synthesis of an amphiphilic miktoarm star terpolymer and combine it with an equivalent diblock copolymer to form polymersomes with controlled surface topology. The three branches are ligated onto a central maleimide moiety in a reaction sequence that exploits various “click” chemistries. The final star was self-assembled with a linear block copolymer to generate a “patchy” surface on vesicles.
Lee, M.T.W., Maruani, A., Chudasama, V.*
J Chem Res, 2016, 40, 1-9.
This article gives an overview of the use of 3,6-pyridazinediones in organic synthesis and chemical biology with an emphasis on recent developments. The properties of pyridazinediones, how they are constructed and how they have been applied in various fields of organic synthesis, medicinal chemistry and chemical biology will be highlighted.
36. Identification of an Active Metabolite of PAR-1 Antagonist RWJ 58259 and Synthesis of Analogues to Enhance its Metabolic Stability
Robinson, E., Knight, E., Smoktunowicz, N., Chambers, R., Inglis, G.G.A., Chudasama, V.*, Caddick S.
Org Biomol Chem, 2016, 14, 3198-3201.
The discontinuation of PAR-1 antagonist RWJ-58259 beyond use as a biological probe is most likely due to it’s short half-life in vivo. However, retention of significant in vivo activity beyond the point where most of the RWJ-58259 had been consumed implies the generation of an active metabolite. Herein we describe the biological activity of a predicted metabolite of RWJ-58259 and the synthesis of analogues designed to enhance the metabolic stability of RWJ-58259.
Knight, E., Robinson, E., Smoktunowicz, N., Chambers, R., Aliev, A. E., Inglis, G.G.A., Chudasama, V.*, Caddick S.
Org Biomol Chem, 2016, 14, 3264-3274.
Vorapaxar is a first-in-class PAR-1 antagonistic drug based on the ent-himbacine scaffold. Detailed in this article are enantioselective and racemic routes to various novel vorapaxar analogues. Biological testing revealed these compounds to have moderate to excellent potencies against PAR-1 with the most potent analogue demonstrating an IC50 of 27 nM.
34. A facile, one-pot procedure for the conversion of aromatic aldehydes to esters, as well as thioesters and amides, via acyl hydrazide intermediates
Maruani, A., Lee, M.T.W, Watkins, G., Akhbar, A.R., Baggs, H., Shamsabadi, A., Richards D.A., Chudasama, V.*
RSC Adv, 2016, 6, 3372-3376.
Herein we present an efficient method for the synthesis of esters from aromatic aldehydes via readily accessible acyl hydrazides. The developed reaction protocol is shown to be tolerant of a range of aromatic aldehydes, bearing various functionalities, as well as being amenable to the synthesis of thioesters and amides.
33. Photochemically re-bridging disulfide bonds and the discovery of a thiomaleimide mediated photodecarboxylation of C-terminal cysteines
Richards D.A., Fletcher, S.A., Nobles, M., Kossen, H., Tedaldi, L., Chudasama, V., Tinker A., Baker, J.R.
Org Biomol Chem, 2016, 14, 455-459.
Described in this work is a novel method for photochemically manipulating peptides and proteins via the installation of cysteine-selective photoactive tags. Thiomaleimides, generated simply by the addition of bromomaleimides to reduced disulfide bonds, undergo [2 + 2] photocycloadditions to reconnect the crosslink between the two cysteine residues. This methodology is demonstrated to enable photoactivation of a peptide by macrocyclisation, and reconnection of the heavy and light chains in an antibody fragment to form thiol stable conjugates. Finally we report on an intriguing thiomaleimide mediated photochemical decarboxylation of C-terminal cysteines, discovered during this study.
32. Site-selective multi-porphyrin attachment enables the formation of a next-generation antibody-based photodynamic therapeutic
Maruani, A., Savoie, H., Bryden, F.,Caddick, S., Boyle, R.W., Chudasama, V.*
Chem Commun, 2015, 51, 15304-15307.
Herein we present a significant step towards next-generation antibody-based photodynamic therapeutics. Site-selective modification of a clinically relevant monoclonal antibody, with a serum-stable linker bearing a strained alkyne, allows for the controlled Cu-free “click” assembly of an in vitro active antibody-based PDT agent using a water soluble azide porpyhrin.
31. A platform for efficient, thiol-stable conjugation to albumin’s native single accessible cysteine
Smith, M.E.B., Caspersen, M.B., Robinson, E., Morais, M., Maruani, A., Nunes, J.P.M., Nicholls, K., Saxton, M.J., Caddick, S., Baker, J.R., Chudasama, V.*
Org Biomol Chem, 2015, 13, 7946-7949.
Herein we report the use of bromomaleimides for the construction of stable albumin conjugates via conjugation to its native, single accessible, cysteine followed by hydrolysis. Advantages over the classical maleimide approach are highlighted in terms of quantitative hydrolysis and absence of undesirable retro-Michael deconjugation.
30. Functional native disulfide bridging enables delivery of a potent, stable and targeted antibody-drug conjugate (ADC)
Nunes, J.P.M., Morais, M., Vassileva V., Robinson E., Rajkumar, V., Smith, M.E.B., Pedley, B., Caddick, S., Baker, J.R., Chudasama, V.*
Chem Commun, 2015, 51, 10624-10627.
Herein we report the use of next generation maleimides (NGMs) for the construction of a potent antibody–drug conjugate (ADC) via functional disulfide bridging. The linker has excellent stability in blood serum and the ADC, armed with monomethyl auristatin E (MMAE), shows excellent potency and cancer cell selectivity in vitro.
29. A plug-and-play approach to antibody-based therapeutics via a chemoselective dual click strategy
Maruani, A., Smith, M.E.B., Miranda, E, Chester, K.A., Chudasama, V.*, Caddick, S.
Nature Commun, 2015, 6, 6645.
Although recent methods for the engineering of antibody–drug conjugates (ADCs) have gone some way to addressing the challenging issues of ADC construction, significant hurdles still remain. There is clear demand for the construction of novel ADC platforms that offer greater stability, homogeneity and flexibility. Here we describe a significant step towards a platform for next-generation antibody-based therapeutics by providing constructs that combine site-specific modification, exceptional versatility and high stability, with retention of antibody binding and structure post-modification. The relevance of the work in a biological context is also demonstrated in a cytotoxicity assay and a cell internalization study with HER2-positive and -negative breast cancer cell lines.
28. Pentafluorophenyl vinyl sulfonate enables efficient, metal-free, radical-based alkene hydroacylation with aldehyde as limiting reagent
RSC Adv, 2015, 5, 44423-44426.
The unique properties of pentafluorophenyl vinyl sulfonate allow for a hitherto unmet feat to be realised; efficient and high yielding, metal-free, radical-based alkene hydroacylation employing aldehyde as limiting reagent. The optimised conditions are shown to work in good yields across a series of aldehydes, thus demonstrating the wide applicability of the developed protocol.
Morgan, R.E., Chudasama, V., Moody, P., Smith, M.E.B., Caddick S.
Org Biomol Chem, 2015, 13, 4165-4168.
Ubiquitination is of great importance as the post-translational modification of proteins with ubiquitin, or ubiquitin chains, facilitates a number of vital cellular processes. Herein we present a facile method of preparing various ubiquitin conjugates under mild conditions using michael acceptors based on dibromo-maleimides and dibromo-pyridazinediones.
26. A mild TCEP-based para-azidobenyl cleavage strategy to transform reversible cysteine thiol labelling reagents into irreversible conjugates
Maruani, A., Alom, S., Canavelli, P., Lee, M., Morgan R.E., Chudasama, V.*, Caddick, S.
Chem Commun, 2015, 51, 5279-5282.
It has recently emerged that the succinimide linkage of a maleimide thiol addition product is fragile, which is a major issue in fields where thiol functionalisation needs to be robust. Herein we deliver a strategy that generates selective cysteine thiol labelling reagents, which are stable to hydrolysis and thiol exchange.
25. Next generation maleimides enable the controlled assembly of antibody-drug conjugatesvia native disulfide bond bridging
Schumacher, F.F., Nunes, J.P.M., Maruani, A., Chudasama, V., Smith, M.E.B., Chester, K.A., Baker, J.R., Caddick, S.
Org Biomol Chem, 2014, 7261-7269.
The advent of Adcetris™ and Kadcyla™, two recently FDA-approved antibody–drug conjugates (ADCs), in the clinic has had a major impact on the treatment of lymphoma and breast cancer patients, respectively, worldwide. Despite these successes many new ADCs fail at various stages of development, often due to shortcomings in the methods used for their assembly. To address this problem we have developed next generation maleimides (NGMs), which specifically re-bridge reduced interchain disulfide bonds and allow the efficient conjugation of small molecules to antibodies, without the need for engineering of the target antibody. The method is site-specific and generates near homogeneous products in good yields. Moreover, adjustment of the reaction conditions allows control of the conjugation in terms of stoichiometry (drug-loading) and site selectivity. Using this method we prepared a series of ADCs from trastuzumab and doxorubicin (DOX) with a controlled drug-to-antibody ratio (DAR) of 1, 2, 3 and 4. All of these constructs were fully active by ELISA and had more than 90% of re-bridged disulfide bonds by CE-SDS when compared to clinical grade antibody. Furthermore, digest experiments of the DAR 2 material revealed that almost all of the drug had been targeted to the Fab arms of the antibody. Thus, NGMs offer a flexible and simple platform for the controlled assembly of ADCs from an antibody.
Moody, P.R., Chudasama, V., Nathani, R.I., Maruani, A., Martin, S., Smith, M.E.B., Caddick, S.
Chem Commun, 2014, 50, 4898-4900.
Designed ankyrin repeat proteins (DARPins) are valuable tools in both biochemistry and medicine. Herein we describe a rapid, simple method for the dual modification of DARPins by introduction of cysteine mutations at specific positions that results in a vast difference in their thiol nucleophilicity, allowing for clean sequential modification.
23. Regioselective and stoichiometrically controlled conjugation of photodynamic sensitizers to a HER2 targeting antibody fragment
Bryden, F., Maruani, A., Savoie, H., Chudasama, V., Smith, M.E.B., Caddick, S., Boyle, R.W.
Bioconjugate Chem, 2014, 25, 611-617.
The rapidly increasing interest in the synthesis of antibody–drug conjugates as powerful targeted anticancer agents demonstrates the growing appreciation of the power of antibodies and antibody fragments as highly selective targeting moieties. This targeting ability is of particular interest in the area of photodynamic therapy, as the applicability of current clinical photosensitizers is limited by their relatively poor accumulation in target tissue in comparison to healthy tissue. Although synthesis of porphyrin–antibody conjugates has been previously demonstrated, existing work in this area has been hindered by the limitations of conventional antibody conjugation methods. This work describes the attachment of azide-functionalized, water-soluble porphyrins to a tratuzumab Fab fragment via a novel conjugation methodology. This method allows for the synthesis of a homogeneous product without the loss of structural stability associated with conventional methods of disulfide modification. Biological evaluation of the synthesized conjugates demonstrates excellent selectivity for a HER2 positive cell line over the control, with no dark toxicity observed in either case.
Browne, L.E., Nunes, J.P.M., Sim, J.A., Chudasama, V., Bragg, L., Caddick, S., North, R.A.
Proc Natl Acad Sci USA, 2014, 111, 521-526.
P2X receptors are trimeric membrane proteins that function as ion channels gated by extracellular ATP. We have engineered a P2X2 receptor that opens within milliseconds by irradiation at 440 nm, and rapidly closes at 360 nm. This requires bridging receptor subunits via covalent attachment of 4,4′-bis(maleimido)azobenzene to a cysteine residue (P329C) introduced into each second transmembrane domain. The cis–trans isomerization of the azobenzene pushes apart the outer ends of the transmembrane helices and opens the channel in a light-dependent manner. Light-activated channels exhibited similar unitary currents, rectification, calcium permeability, and dye uptake as P2X2 receptors activated by ATP. P2X3 receptors with an equivalent mutation (P320C) were also light sensitive after chemical modification. They showed typical rapid desensitization, and they could coassemble with native P2X2 subunits in pheochromocytoma cells to form light-activated heteromeric P2X2/3 receptors. A similar approach was used to open and close human acid-sensing ion channels (ASICs), which are also trimers but are unrelated in sequence to P2X receptors. The experiments indicate that the opening of the permeation pathway requires similar and substantial movements of the transmembrane helices in both P2X receptors and ASICs, and the method will allow precise optical control of P2X receptors or ASICs in intact tissues.
Akhbar, A.R., Chudasama, V.*, Fitzmaurice, R.J., Powell, L., Caddick, S.
Chem Commun, 2014, 50, 743-746.
In this communication we describe a novel strategy for the formation of valuable diaryl and aryl alkyl ketones from acyl hydrazides. A wide variety of ketones are prepared and the mild reaction conditions allow for the use of a range of functionalities, especially in the synthesis of diaryl ketones.
Cal, P.M.S.D., Frade, R.F.M., Chudasama V., Cordeiro, C., Caddick, S., Gois, P.M.P.
Chem Commun, 2014, 50, 5261-5263.
Herein we present the synthesis of fluorescent 2-acetylbenzeneboronic acids that undergo B–N promoted conjugation with lysozyme and N-(2-aminoethyl) folic acid (EDA-FA), generating conjugates that are selectively recognized and internalized by cancer cells that over-express folic acid receptors.
19. Motional timescale predictions by molecular dynamics simulations: Case study using proline and hydroxyproline sidechain dynamics
Aliev A. E., Kulke, M., Khaneja, H. S,. Chudasama V., Sheppard, T. D., Lanigan R. M. Proteins, 2014, 82, 195-215.
We propose a new approach for force field optimizations which aims at reproducing dynamics characteristics using biomolecular MD simulations, in addition to improved prediction of motionally averaged structural properties available from experiment. As the source of experimental data for dynamics fittings, we use 13C NMR spin-lattice relaxation times T1 of backbone and sidechain carbons, which allow to determine correlation times of both overall molecular and intramolecular motions. For structural fittings, we use motionally averaged experimental values of NMR J couplings. The proline residue and its derivative 4-hydroxyproline with relatively simple cyclic structure and sidechain dynamics were chosen for the assessment of the new approach in this work. Initially, grid search and simplexed MD simulations identified large number of parameter sets which fit equally well experimental J couplings. Using the Arrhenius-type relationship between the force constant and the correlation time, the available MD data for a series of parameter sets were analyzed to predict the value of the force constant that best reproduces experimental timescale of the sidechain dynamics. Verification of the new force-field (termed as AMBER99SB-ILDNP) against NMR J couplings and correlation times showed consistent and significant improvements compared to the original force field in reproducing both structural and dynamics properties. The results suggest that matching experimental timescales of motions together with motionally averaged characteristics is the valid approach for force field parameter optimization. Such a comprehensive approach is not restricted to cyclic residues and can be extended to other amino acid residues, as well as to the backbone.
18. SMITH, M., BAKER, J., CADDICK, S., CHUDASAMA, V. (2014). Thiol protecting group. Granted Patent EP2464654.
17. Metal-free, hydroacylation of C=C and N=N bonds via aerobic C-H activation of aldehydes, and reaction of the products thereof
Chudasama, V., Akhbar, A.R., Bahou, K.A., Fitzmaurice, R.J., Caddick, S.
Org Biomol Chem, 2013, 11, 7301-7317.
In this report, a thorough evaluation of the use of aerobically initiated, metal-free hydroacylation of various C￼C and N￼N acceptor molecules with a wide range of aldehydes is presented. The aerobic-activation conditions that have been developed are in sharp contrast to previous conditions for hydroacylation, which tend to use transition metals, peroxides that require thermal or photochemical degradation, or N-heterocyclic carbenes. The mildness of the conditions enables a number of reactions involving sensitive reaction partners and, perhaps most significantly, allows for α-functionalised chiral aldehydes to undergo radical-based hydroacylation with complete retention of optical purity. We also demonstrate how the resulting hydroacylation products can be transformed into other useful intermediates, such as γ-keto-sulfonamides, sultams, sultones, cyclic N-sulfonyl imines and amides.
16. SMITH, M., BAKER, J., SCHUMACHER, F., CADDICK, S., CHUDASAMA, V., MARUANI, A. (2013). Chemical modification of antibodies. Patent application WO/2013/132268.
15. SMITH, M., BAKER, J., CADDICK, S., CHUDASAMA, V. (2013). Thiol protecting group. Granted Patent US13/389,625.
Castañeda, L., Maruani, A., Schumacher, F.F., Miranda, E., Chudasama, V., Chester, K.A., Baker, J.R., Smith, M.E.B., Caddick, S.
Chem Commun, 2013, 49, 8187-8189.
In this communication we describe a novel acid-cleavable linker strategy for antibody–drug conjugation. Functional disulfide bridging of the single interchain disulfide bond of a trastuzumab Fab fragment yields a homogeneous antibody–drug conjugate bearing a thiomaleamic acid linker. This linker is stable at physiological pH and temperature, but quantitatively cleaves at lysosomal pH to release the drug payload.
13. A Novel Approach to the Site-Selective Dual Labelling of a Protein via Chemoselective Cysteine Modification
Nathani, R.I., Moody, P.R., Chudasama, V., Smith M.E.B., Fitzmaurice, R.J., Caddick, S.
Chem Sci, 2013, 4, 3455-3458.
Local protein microenvironment is used to control the outcome of reaction between cysteine residues and 2,5-dibromohexanediamide. The differential reactivity is exploited to introduce two orthogonal reactive handles onto the surface of a double cysteine mutant of superfolder green fluorescent protein in a regioselective manner. Subsequent elaboration with commonly used thiol and alkyne containing reagents affects site-selective protein dual labelling.
Castañeda, L., Wright, Z.V.F., Marculescu C., Tran, T.M., Chudasama V., Maruani, A., Hull E.A., Nunes J.P.M., Fitzmaurice R.J., Smith, M.E.B., Jones, L.H., Caddick, S., Baker, J.R. Tetrahedron Lett, 2013, 54, 3493-3495.
Bromomaleimides are useful building blocks in synthesis and powerful reagents for the selective chemical modification of proteins. A mild new synthesis of these reagents is described, along with the convenient transferability of the approach to dithiomaleimides and bromopyridazinediones.
Nathani, R.I., Chudasama, V., Ryan, C.P., Moody P.R., Morgan, R.E., Fitzmaurice R.J., Smith, M.E.B., Baker, J., Caddick, S.
Org Biomol Chem, 2013, 2408-2411.
Reversible protein biotinylation is readily affected via conjugation with a bromomaleimide-based reagent followed by reductive cleavage. The intermediate biotinylated protein constructs are stable at physiological temperature and pH 8.0. Quantitative reversibility is elegantly delivered under mild conditions of using a stoichiometric amount of a bis-thiol, thus providing an approach that will be of general interest in chemical biology and proteomics.
Moody, P., Smith, M. E., Ryan, C. P., Chudasama, V., Baker, J. R., Molloy, J., Caddick, S.
Chembiochem, 2012, 13, 39-41.
Bromomaleimides are versatile scaffolds that allow facile conjugation of thiolated biomolecules. Here we demonstrate that bromomaleimide-linked GFP–rhodamine FRET pairs cleave in the cytoplasm of mammalian cells. We believe that bromomaleimide scaffolds provide a potential core structure for prodrugs designed to release bioactive cargo following cell internalisation.
9. E- and Z-Stereoselectivity in the preparation of enamides from glycidyl sulfonamides and carbamates
Brown, J. A., Chudasama, V., Giles M. E., Gill, D. M., Keegan, P. S., Kerr, W. J., Munday R. H., Griffin, K., Watts, A.
Org Biomol Chem, 2012, 10, 509-511.
Treatment of glycidyl sulfonamides with LDA delivers the corresponding enesulfonamide with good selectivity for the E-isomer, whereas the corresponding carbamates exhibit selectivity for the Z-enecarbamate. An E1cB elimination mechanism proceeding from a substrate–base chelate complex is advanced as rationalisation of the latter set of Z-selective outcomes.
8. CADDICK, S., SMITH, M., BAKER, J., CHUDASAMA V. (2011). Thiol protecting group. Patent application WO/2011/018612
7. CADDICK, S., SMITH, M., BAKER, J., CHUDASAMA V. (2011). Reversible covalent linkage of functional moieties. Patent application WO 2011/018611
Chudasama, V., Ahern, J. M., Dhokia, D. V., Fitzmaurice, R. J., Caddick, S.
Chem Commun, 2011, 47, 3269-3271.
Herein we report the functionalisation of aldehydesvia hydroacylation of azodicarboxylates. A range of functionalised aldehydes are employed as the limiting reagent including chiral non-racemic aldehydes bearing α-stereocentres which are functionalised giving access to enantiomerically pure products. The resultant hydrazides can be employed as acyl donors in the synthesis of amides.
Chudasama, V., Ahern, J. M., Fitzmaurice, R. J., Caddick, S.
Tetrahedron Lett, 2011, 52, 1067-1069.
γ-Ketophosphonates are commonly employed as non-hydrolysable phosphate mimetics and as tools in synthesis. The synthesis of γ-ketophosphonates under mild conditions via interception of acyl radicals generated by aldehyde auto-oxidation is described.
Chudasama, V., Smith, M. E., Schumacher, F. F., Papaioannou, D., Waksman, G., Baker, J. R., Caddick, S.
Chem Commun, 2011, 47, 8781-8783.
Bromopyridazinedione-mediated bioconjugation to a cysteine containing protein and a disulfide containing peptide is described. The conjugates are cleavable in an excess of thiol, including cytoplasmically-relevant concentrations of glutathione, and show a high level of hydrolytic stability. The constructs have the potential for four points of chemical attachment.
Chudasama, V., Fitzmaurice, R. J., Ahern, J. M., Caddick, S.
Chem Commun, 2010, 46, 133-135.
Herein we report a mild, facile method for the preparation of 1,4-keto-sulfonates and sulfones onwater. Further synthetic manipulations can result in products that are not readily accessed by hydroacylation of electron rich alkenes.
Chudasama, V., Fitzmaurice, R. J., Caddick, S.
Nat Chem, 2010, 2, 592-596.
The development of methods for carbon–carbon bond formation under benign conditions is an ongoing challenge for the synthetic chemist. In recent years there has been considerable interest in using selective C–H activation as a direct route for generating reactive intermediates. In this article, we describe the use of aldehyde auto-oxidation as a simple, clean and effective method for C–H activation, resulting in the generation of an acyl radical. This acyl radical can be used for carbon–carbon bond formation and herein we describe the application of this method for the hydroacylation of α,β-unsaturated esters without the requirement of additional catalysts or reagents. This methodology generates unsymmetrical ketones, which have been shown to have broad use in organic synthesis.
Chudasama, V., Wilden J. D.
Chem Commun, 2008, 3768-3770.
A variety of five-membered ring oxazoles have been synthesised with complete regiocontrol and without the requirement for ring oxidationvia a reaction sequence based on a vinyl sulfonamide template.