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The structure of alahopcin (nourseimycin) (1), a new dipeptide antibiotic isolated from Streptomyces, has been established to be (2S, 3R)-2-[(L-alanyl)amino]-4-formyl-3-(hydroxy-aminocarbonyl)butyric acid. 1 exists in two cyclic hemiacetal type tautomers formed by intramolecular ring closure between the hydroxyamino group and the formyl group in aqueous solution. The structure of the new weakly acidic amino acid (2), a constituent of 1, is revealed to be (2S, 3R)-2-amino-4-formyl-3-(hydroxyaminocarbonyl)butyric acid, and 2 also exists in two cyclic hemiacetal type tautomers in aqueous solution.

An aziridine ring-formation involving the reaction of adjacent amino and alcohol groups with triphenylphosphine, carbon tetrachloride, and triethylamine was applied at the 2′ and 3′ positions of butirosin A ( 1a ) and B ( 1b ). The amino groups at the 2′ position of 1a and 1b were p -methoxybenzylated to increase the nucleophilicity of the nitrogen atom and to avoid the formation of a P-N linkage, and the N-p -methoxybenzyl derivatives were converted into the aziridine derivatives, which were then subjected to hydrogenolysis and removal of the protecting groups to give 3′-deoxybutirosin A ( 7a ) and B ( 7b ), respectively. This new method is compared with the conventional N, O -protecting method that involves several complex steps.

The chemical structure of validamycin A, a new water-soluble weakly basic antibiotic, was shown to be (1).

Microbial degradation of validamycin A gave a new unsaturated aminocyclitol (5) with the 1S-configuration, establishing the structure (1) of the unsaturated cyclitol portion of validamycin A; the structure of epivalidamine (6), a new aminocyclitol derived from dihydrovalidamycin A was also elucidated.