(Z)-Oxopropene-1,3-diyl, a Linker for the Conjugation of the Thiol Group of Cysteine with Amino-Derivatized Drugs

A thiol-selective and acid-stable protein modification strategy using an electron-deficient yne reagent

A protein modification strategy was developed based on a thiol-yne click reaction using an electron-deficient yne reagent. This approach demonstrated exceptional selectivity towards thiols and exhibited rapid kinetics, resulting in conjugates with superior acid stability. The conjugation of IgG with an indole-derived fluorophore was achieved for the imaging of PD-L1 in cancer cells.

Phenylpropynones as Selective Disulfide Rebridging Bioconjugation Reagents

Simple 1-phenylpropynones undergo a selective double thia-Michael addition with thiols in buffered media, yielding an interesting dithioacetal linkage joining two thiols. The reactivity of various Michael-alkyne reagents is compared in this chemoselective, atom economical, and non-oxidative cross-linking of two thiols. The stability and chemical reactivity of the dithioacetal links are studied, and the utility of the disulfide targeting bioconjugation methodology is shown by the selective rebridging of native cyclic peptides after the reductive cleavage of their disulfide bridge.

Recent developments in chemical conjugation strategies targeting native amino acids in proteins and their applications in antibody-drug conjugates

Many fields in chemical biology and synthetic biology require effective bioconjugation methods to achieve their desired functions and activities. Among such biomolecule conjugates, antibody-drug conjugates (ADCs) need a linker that provides a stable linkage between cytotoxic drugs and antibodies, whilst conjugating in a biologically benign, fast and selective fashion. This review focuses on how the development of novel organic synthesis can solve the problems of traditional linker technology. The review shall introduce and analyse the current developments in the modification of native amino acids on peptides or proteins and their applicability to ADC linker. Thereafter, the review shall discuss in detail each endogenous amino acid's intrinsic reactivity and selectivity aspects, and address the research effort to construct an ADC using each conjugation method.

Sulfuroxygen interaction-controlled (Z)-selective anti-Markovnikov vinyl sulfides

The sulfur oxygen (SO) interaction was used herein to obtain (Z)-selective anti-Markovnikov vinyl sulfides from the addition of thiyl radicals to terminal alkynes. DFT calculations predicted that SO interaction originated from the delocalization of the lone-pair of the carbonyl oxygen to the adjacent σ* orbital of the S atom of C-S.

Computational Study of the Addition of Methanethiol to 40+ Michael Acceptors as a Model for the Bioconjugation of Cysteines

A long series of Michael acceptors are studied computationally as potential alternatives to the maleimides that are used in most antibody-drug conjugates to link Cys of mAbs with cytotoxic drugs. The products of the reaction of methanethiol (CH3SH/MeSH, as a simple model of Cys) with N-methylated ethynesulfonamide, 2-ethynylpyridinium ion, propynamide, and methyl ethynephosphonamidate (that is, with HC≡C-EWG) are predicted by the M06-2X/6-311+G(d,p) method to be thermodynamically more stable, in relation to their precursors, than that of MeSH with N-methylmaleimide and, in general, with H2C═CH-EWG; calculations with AcCysOMe and tBuSH are also included. However, for the addition of the anion (MeS-), which is the reactive species, the order changes and N-methylated 2-vinylpyridinium ion, 2,3-butadienamide, and maleimide may give more easily the anionic adducts than several activated triple bonds; moreover, the calculated ΔG⧧ values increase following the order HC≡C-SO2NHMe, N-methylmaleimide, HC≡C-PO(OMe)NHMe, and HC≡C-CONHMe. In other words, MeS- is predicted to react more rapidly with maleimides than with ethynephosphonamidates and with propynamides, in agreement with the experimental results. New mechanistic details are disclosed regarding the advantageous use of some amides, especially of ethynesulfonamides, which, however, are more prone to double additions and exchange reactions.

BMS Derivatives C7-Linked to β-Cyclodextrin and Hyperbranched Polyglycerol Retain Activity against R5-HIV-1NLAD8 Isolates and Can Be Deemed Potential Microbicides

Amides from indole-3-glyoxylic acid and 4-benzoyl-2-methylpiperazine, which are related to entry inhibitors developed by Bristol-Myers Squibb (BMS), have been synthesized with aliphatic chains located at the C7 position of the indole ring. These spacers contain an azido group suitable for the well-known Cu(I)-catalyzed (3+2)-cycloaddition or an activated triple bond for the nucleophilic addition of thiols under physiological conditions. Reaction with polyols (β-cyclodextrin and hyperbranched polyglycerol) decorated with complementary click partners has afforded polyol-BMS-like conjugates that are not cytotoxic (TZM.bl cells) and retain the activity against R5-HIV-1_NLAD8 isolates. Thus, potential vaginal microbicides based on entry inhibitors, which can be called of 4^th generation, are reported here for the first time.

Antibody-Drug Conjugate Using Ionized Cys-Linker-MMAE as the Potent Payload Shows Optimal Therapeutic Safety

Monomethyl auristatin E (MMAE) is the most popular and widely used cytotoxin in the development of antibody-drug conjugates (ADCs). However, current MMAE-based ADCs are all constructed using cleavable linkers, and this design concept still has insurmountable drawbacks. Their potential instabilities and lipophilic MMAE-induced “bystander effect” inevitably increase the toxicity to normal tissues. Herein, we overturn previous negative views of MMAE-based ADCs with non-cleavable linkers and propose using ionized L-Cysteine (Cys)-linker-MMAE as a novel payload, which can ingeniously enrich and enter tumor cells through receptor-mediated endocytosis of antibodies while its lower permeability helps to avoid further off-target toxicity. We demonstrate that Cys-linker-MMAE maintains high potency similar to free MMAE at the tubulin molecular level and can also be efficiently released in target cells. As a result, the preferred ADC (mil40-15) not only exhibits ideal plasma stability and maintains potent cytotoxicity as MMAE (IC₅₀: 10⁻¹¹ M), but also shows improved safety with lower bystander toxicity (IC₅₀: 10⁻⁹ M), its maximum tolerated dose approaching the level of the naked antibody (160 mg/kg). This study indicated that Cys-linker-MMAE has the potential as a potent payload for ADCs, which is expected to provide novel strategies for the development of MMAE-based ADCs.

Zinc complexes supported by pyridine-N-oxide ligands: synthesis, structures and catalytic Michael addition reactions

Zinc complexes supported by pyridine-N-oxide ligands show highly efficient catalysis for Michael addition reaction. The NMR and MS experiments analysis displays intermediate [Zn(SR)₂(HSR)₄] has real catalytic activity for the addition reactions.