The protease-catalyzed synthesis of amino acid est-carbohydrate conjugates as glycopeptide analogues has been achieved in a highly regioselective and carbohydrate-specific manner using amino acid vinyl ester acyl donors and minimally or completely unprotected carbohydrate acyl acceptors, which together probed active sites of proteases to reveal yield efficiencies that are modulated by the carbohydrate C-2 substitutent, and that may be exploited to allow selective one-pot syntheses.
2‐(Pyrrolidinyl)thiazole‐4‐carboxylic acid 5d, 2‐(1‐aminoalkyl) thiazole‐4‐carboxamides and hydrazides 8, 10 have been synthesized using alanine, valine, and proline as educts. In addition oxazole amino acids derived from leucine 20a and alanine 20b and some peptides 13, 14, 16 containing the 5‐ring heterocyclic backbone modifications have been prepared. The thiazole and oxazole containing amino acids and peptides showed moderate antibacterial activity in vitro against various Gram‐positive (Staphylococcus aureus, Bacillus cereus, etc.) and Gram‐negative (Escherichia coli, Proteus vulgaris, etc.) bacteria, fungi (Candida albicans), and yeast (Saccharomyces cerevisae, etc.).
Some new thioamides and thiazoles have been synthesized using canavanine, S-cysteine, homo-S-cysteinesulfonamides and their N-omega aminoethylated derivatives as adducts in order to investigate the structure-antimicrobial activity relationships. The compounds showed substantial antibacterial activity in vitro against various gram-positive (Staphylococcus aureus, Bacillus cereus etc.) and gram-negative (Escherichia coli, Proteus vulgaris etc.) bacteria. These findings indicate that the presence of the thiazole residue is an essential factor for the antibacterial effect.
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