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The existence of an isomeric form in equilibrium with the major component of FK-520 in polar solutions has been demonstrated. This minor component has been isolated in high yield and purity by a novel crystallization strategy and preparative HPLC. The equilibrium product was characterized by NMR and MS.

The preparation of 4-de-N-methylfortimicin A analogs as well as the preparation of 4-de-N-methyl-4-N-(beta-aminoethyl)-4-N-ethylfortimicin B is reported. It was shown that the 4-N-methyl group in fortimicin analogs is essential for antibacterial activity since neither the 4-de-N-methylfortimicin A nor the 4-de-N-methyl-4-N-(beta-aminoethyl)-4-N-ethylfortimicin B exhibited useful biological activity.

The nature of the products obtained from the reaction of chelocardin (1) and the model compound 2-acetyldimedone (5) with a variety of amines was investigated. It was observed that amines react with β-triketones having an exocyclic carbonyl side-chain to give exclusively β,β′-diketoenamines with substitution at the side-chain carbonyl.

7-Deoxy-4(R)-dihydrospectinomycin (7) has been prepared and its structure firmly established by proton magnetic resonance and high resolution mass spectrometry. This spectinomycin analog is devoid of antibiotic activity.

The structures of fortimicins A and B have been determined by PMR, CMR, mass spectra and CD combined with chemical degradations. Both antibiotics are pseudodisaccha-rides and incorporate a novel aminocyclitol, fortamine. Incontrast to the diaminocyclitol moieties of known aminoglycosides, fortamine is a 1, 4-diamine, contains both N- and O-methyl groups and possesses chiro stereochemistry. Both antibiotics are glycosides of 6-epi-pur-purosamine B, but fort imicin A differs from fortimicin B by being a glycyl amide.

The structures of seldomycin factors 1 and 2 have been determined by consideration of chemical degradation and spectral properties. Factor 1, also known as XK-88-1, is shown to be 6-O-(2-amino-2-deoxy-alpha-D-xylopyranosyl) paromamine (1) and factor 2, also known as XK-88-2, is shown to be 4'-deoxy-neamine (2). Mass spectral evidence has been obtained that suggests the most probable structure for seldomycin factor 3, also known as XK-88-3, is 6'-amino-6'-deoxyseldomycin factor 1 (12).

The biotransformation of lankamycin and congeners darcanolide and 11-acetyllankolide by a blocked mutant of the erythromycin-producing organism Streptomyces erythreus, which cannot synthesize erythromycin without supplementation with erythromycin precursors, was investigated. Darcanolide and 11-acetyllankolide were converted into the corresponding 15-deoxy-15-oxo derivatives. Lankamycin was transformed to 15-deoxy-15-oxolankamycin, 4"-deacetyl-l5-deoxy-15-oxolankamycin and 3'-de-O-methyllankamycin. None of the derivatives possessed high antimicrobial activity.

13C-NMR studies have confirmed the structures of (8S)-8-hydroxyerythromycins A- and B-6, 9;9, 11-acetal proposed by KROWICKI and ZAMOJSKI2, 3) for the products of the m-chloroperbenzoic acid oxidation of 8, 9-anhydroerythromycins A- and B-6, 9-hemiacetal. The preparations of (8S)-8-methylthiomethoxy- and (8S)-8-methoxyerythromycin B-6, 9;9, 11-acetals are described. The latter are stable in aqueous acetic acid under conditions which convert (8S)-8-hydroxyerythromycin B-6, 9;9, 11-acetalinto (8S)-8-hydroxyerythromycin B. In a paper describing the preparation of the C8-epimeric 8-hydroxyerythromycins B, we reported1) that buffered m-chloroperbenzoic acid oxidation of 8, 9-anhydroerythromycin B-6, 9-hemiacetal (1), followed by catalytic reduction of the resulting N-oxide to the free amine, gave (8S, 9S)-8, 9-anhydroerythromycin B-6, 9-hemiacetal-8, 9-epoxide (2). Our assignment of structure 2 was based on the expected course of olefin epoxidation with peracids and with apparently compatible spectral properties. In addition, the facile conversion of 2 to (8S)-8-hydroxyerythromycin B (3) in aqueous acetic acid was expected for the strained epoxy spiroacetal structure (2).

The structure of XK-62-2 has been firmly established to be 6'-N-methylgentamicin C1a (3) by application of spectroscopic methods in conjunction with chemical degradation. The data obtained in every case are completely consistent with the proposed structure.

7-Epi-spectinomycin (9) and 7-epi-4(R)-dihydrospectinomycin (10) have been prepared and their structures firmly established by proton magnetic resonance. Both of these spectinomycin analogs are devoid of antibiotic activity.

The conversion of fortimicin E, a minor metabolite from the Micromonospora olivoasterospora fermentation which also produces fortimicin A and fortimicin B, to four 4-N-aminoacylfortimicins E was accomplished. The new 4-N-aminoacylfortimicins E showed only weak antimicrobial activity against several Gram-negative and Gram-positive microorganisms.