Venkataraman Ganesh

In this review, we present the recent advances in the synthesis and reactivity of vinylcyclopropanes (VCPs). Various important methodologies involving ylides, carbenoid chemistry, metal-mediated cycloaddition reactions, and allylic cyclization methodologies for the synthesis of VCPs are described. Based on the type of VCPs, their reactivity is dealt under electrophile-, radical-, and nucleophile-mediated reactions. Several examples from transition-metal-mediated ring-opening reactions are discussed. 1 Introduction 2 Synthetic Routes to Vinylcyclopropanes 2.1 Ylide Chemistry 2.2 Transition-Metal-Mediated Synthesis 3 Reactivity of Vinylcyclopropanes 3.1 Electrophile-Mediated Ring-Opening Reactions 3.2 Radical-Mediated Ring-Opening Reactions 3.3 Nucleophile-Mediated Ring-Opening Reactions 3.4 Transition-Metal-Mediated Ring-Opening Reactions 4 Conclusion

The x-ray crystal structure of the tetrameric T-antigen-binding lectin from peanut, M(r) 110,000, has been determined by using the multiple isomorphous replacement method and refined to an R value of 0.218 for 22,155 reflections within the 10- to 2.95-A resolution range. Each subunit has essentially the same characteristic tertiary fold that is found in other legume lectins. The structure, however, exhibits an unusual quaternary arrangement of subunits. Unlike other well-characterized tetrameric proteins with identical subunits, peanut lectin has neither 222 (D2) nor fourfold (C4) symmetry. A noncrystallographic twofold axis relates two halves of the molecule. The two monomers in each half are related by a local twofold axis. The mutual disposition of the axes is such that they do not lead to a closed point group. Furthermore, the structure of peanut lectin demonstrates that differences in subunit arrangement in legume lectins could be due to factors intrinsic to the protein molecule and, contrary to earlier suggestions, are not necessarily caused by interactions involving covalently linked sugar. The structure provides a useful framework for exploring the structural basis and the functional implications of the variability in the subunit arrangement in legume lectins despite all of them having nearly the same subunit structure, and also for investigating the general problem of "open" quaternary assembly in oligomeric proteins.

Click chemistry has played a significant role as a rapid and versatile strategy for conjugating two molecular fragments under very mild reaction conditions. Introduction of ferrocene-derived triazole systems using click chemistry has attracted enormous interest in various fields due to its potential applications in electrochemical techniques for detection and sensing. The present discussion focuses on the synthesis of ferrocene-triazole and the importance of using a CuAAC reaction for such conjugation. Applications of ferrocene-based click reactions in conjugate chemistry, asymmetric catalysis, medicinal chemistry, host-guest interactions, and materials chemistry have been highlighted.

Direct catalytic addition of alkylnitriles to aldehydes allows for an atom-economical access to β-hydroxynitriles under proton transfer conditions. Direct use of alkylnitriles as pronucleophiles has been hampered due to their low acidity resulting in an inability to generate α-cyano carbanions in a catalytic manner. A transition metal/N-heterocyclic carbene (NHC) complex prepared from [{Rh(OMe)(cod)}2] and an imidazolium-based carbene was identified as an effective catalyst to promote the reaction with as little as 1.25 mol% of catalyst loading. The corresponding Rh complex, derived from chiral triazolium salt, rendered the reaction enantioselective, albeit with moderate enantioselectivity.

A comprehensive study of a general and effective one-step procedure for the synthesis of beta-sulfonamidodisulfides directly from N-tosyl aziridines in a regio- and stereospecific manner under neutral conditions without the use of any Lewis acid or base has been reported. This methodology is extended to the synthesis of an optically pure cyclic seven-membered disulfide 29. Synthesis of a variety of beta-sulfonamidosulfides involving tandem, multistep reactions in one pot is also reported.