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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 6-0-(2-amino-2-deoxy-a-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 seldomycin factors are a group of aminoglycoside antibiotics isolated from the fermentation of a novel species of Streptomycetes, S. hofunensis. The mixture of antibiotics consists of four compounds previously designated XK-88-1, -2, -3, and -5 now generically named seldomycin factors 1, 2, 3 and 5. Previous papers in this series1,2) have presented the fermentation, isolation and general characterization of these compounds. This paper will outline the evidence for the structures of seldomycin factors 1 and 2 and offer a suggestion for the probable structure of factor 3. The following paper in this series3) presents the structural evidence for seldomycin factor 5, therapeutically the most significant. Structure of Seldomycin Factor 1The 100 MHz PMR spectrum of a D2O solution of seldomycin factor 1 free base (1) (Fig. 1) indicated that this material is a pseudo-trisaccharide since two anomeric resonances are visible at low field. The anomeric coupling constants are both 4.0 Hz compatible with the x-D anomeric configuration generally found in other pseudo-trisaccharide aminoglycosides. Spin decoupling experiments revealed that both anomerics are affected by irradiation at 3.23 ppm. These relatively high field chemical shifts of H-2' and H-2" require that both are shielded by amine nitrogens and indicate that both sugars are 2-deoxy-2-amino derivatives.

Seldomycin factor 5 is shown to be 4-0-[2,6-diamino-2,4,6-trideoxy-a-D-xylo-hexo. pyranosyl]-6-O-[2, 3-diamino-2, 3-dideoxy-4-O-methyl-a-D-xylo-pyranosyl]-2-deoxystreptamine.Seldomycin factor 5 is the most active antibiotic isolated from the fermentation broth of Streptomyces hofunensis. The taxonomy and fermentation of this organism have been described.) The isolation procedure and the physical properties'' of seldomycin factor 5 characterize this antibiotic as a watersoluble basic compound of the aminoglycoside class. The antibacterial spectrum of seldomycin factor 5 indicates that this compound is probably a close relative of the kanamycin-gentamicin group. Moreover, the activity or lack of activity of seldomycin factor 5 against a number of isolates having known mechanisms of resistance, involving in each case the modification of a functional group, was strongly suggestive of the absence or presence of these groups in the structure of seldomycin factor 5.2) Spectrometric analysis of seldomycin factor 5 and a number of degradation products has allowed for the definition of the structure and stereochemistry of this antibiotic. Results and DiscussionThe mass spectrum of the free base of seldomycin factor 5 (Table 1) shows an M+ I peak at 451 amu in agreement with the molecular formula C18H38N6O72) The degradation pattern is indicative of a diglycoside of 2-deoxystreptamine in which each of the three basic carbohydrate units has the same molecular formula, namely C6H,4N203. The per-N-acetyl-per-O-trimethylsilyl derivatives) of seldomycin factor 5 was prepared and the mass spectrum obtained from this derivative (Table 2, Fig. 1) indicates the presence of six primary or secondary amino groups in the parent molecule, two in each of the subunits. Also, each of two adjacent subunits of the parent bears an hydroxyl group.++ Also known as XK-88-5 * Present address: