The genesis and development of the 4,6-O-benzylidene acetal method for the preparation of β-mannopyranosides are reviewed. Particular emphasis is placed on the influence of the various protecting groups on stereoselectivity and these effects are interpreted in the framework of a general mechanistic scheme invoking a series of solvent-separated and contact ion pairs in dynamic equilibrium with a covalent α-glycosyl trifluoromethanesulfonate.

A wide variety of carboxylic acids in the form of their salts condense with aryl isocyanates at room temperature with loss of carbon dioxide to give the corresponding amides in high yield. Application of the reaction to acyl isocyanates gives unsymmetric imides. The reaction is compatible with hydroxyl groups and both Fmoc and Boc protecting groups for amines and is applicable to aliphatic, aromatic, and heteroaromatic acids.

Thiocarboxylates, prepared conveniently by cleavage of 9-fluorenylmethyl or trimethoxybenzyl thioesters, react at room temperature with isocyanates and isothiocyanates to give amide bonds in good to excellent yield. A carboxylate salt is also shown to react with an electron-deficient isocyanate to give the corresponding amide in excellent yield at room temperature.Given the widespread availability of amines and of carboxylic acids, amide bond forming reactions are necessarily some of the most widely applied transformations in parallel synthesis and combinatorial chemistry. The needs for atom ecomony, ever milder conditions, and greater selectivity combine to drive the search for new and improved methods for the formation of amide bonds. 1 The condensation of isocyanides with carboxylic acids has recently received much interest in this regard, 2 and this despite the relatively limited range of commercially available isocyanides and the somewhat forcing reaction conditions. Our attention was caught by a little known reaction 3 involving condensations of the much more widely available isocyanates and isothiocyanates with monothiocarboxylates which result in the formation of amides with loss of a simple, volatile byproduct, carbon oxysulfide or carbon disulfide, respectively. Although this reaction was described in 1973 for use with very simple substrates it has seen very limited application subsequently, 4 perhaps due to the relative paucity of commercially available thioacids. 5 We reasoned that the advent of convenient mild methods for thioacid synthesis 6 would combine with this reaction to afford a convenient and mild method for amide formation, and report here that this is indeed the case. In addition, we report Dcrich@icsn.cnrs-gif.fr.

No abstract

Glycosyl donors containing a double bond between C2 and C3 were designed by mimicking the reaction mechanism of lysozyme-initiated hydrolysis of mucopolysaccharides. It was found that, under various glycosylation conditions, the reactivities of 2,3-unsaturated glycosyl acetates were significantly higher, while those of the corresponding 2,3-unsaturated-4-keto glycosyl acetates were much lower than those of the corresponding 2,3-dideoxy (2,3-saturated) glycosyl acetates. Based on these results, chemoselective glycosylations were effectively realized via combinatorial techniques in short-steps using three types of glycosyl donors to construct several types of deoxyoligosaccharides. Furthermore, the highly reactive 2,3-unsaturated glycosyl acetates were found to be useful in the synthesis of the O-glycosides of low reactive tertiary alcohols.

No abstract

No abstract

A series of novel peptide-based β-thiolactones were synthesized and assayed for cytotoxicity against several human cancer cell lines, where they showed greater activity than the corresponding β-lactones and β-lactams. Several of the β-thiolactones prepared showed strong inhibitory activity in vitro against human cathepsins B and L.