Carboxamides pyridine analogues

By using this methodology, a new and useful procedure for macrocyclization of linear peptides has been advanced. The side chains of natural amino acids, such as tyrosine, lysine, and histidine, were allowed to react intramolecularly with pendant carboxamide derivatives of pyridine A-oxides, which were selectively activated by the phosphonium salt, PyBroP (Scheme 18) [44]. The reaction proved to be mild, rapid, and efficient with a potentially large substrate scope. A great deal of examples can be demonstrated, including a novel aza-analogue of the ring system of vancomycin. 

Four analogues 134 (X = OH, F Y = O, CF2) of tiazofurin adenine dinucleotide (TAD) have been synthesized, and both 2-(p-D-ribofuranosyl)-pyridine-6-carboxamide and 3(P-D-ribofuranosyl)-pyridine-S-carboxamide have been converted into their NAD analogues, the latter one proving to be a good inhibitor of IMP dehydrogenase. ... 

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