The indole nucleoside antibiotics neosidomycin 5 and SF-2140 3 have been synthesized. Methyl 4deoxy-2,3-0-isopropylidene-a-~-/yxo-hexopyranoside 8 was converted into methyl 1 -chloro-l,4dideoxy-2,3-di-O-pivaloyl-~-~-/yxo-hexopyranuronate 33 in five steps. Silver(i) -catalysed coupling of compound 33 with 3-(cyanomethyl) indole 20 gave stereoselectively an a-nucleoside which was converted into methyl 1 -[3-(carbamoylmethyl) indol-1 -yl] -1.4-dideoxy-a-o-/yxo-hexopyranuronate (neosidomycin, 5). Coupling of compound 33 to 3-cyanomethyl-4-methoxyindole 23 by the sodium salt procedure, and subsequent deacylation, gave methyl 1 -(3-cyanomethyl-4-methoxyindol-1 -yl) -1,4-dideoxy-a-~-/yxo-hexopyranuronate (SF-21 40, 3). Neosidomycin, SF-21 40, and their 0acyl derivatives adopt a conformation which differs from that of 1 -(6-O-benzoyl-4-deoxy-2,3-0pivaloyl-~-~-/yxo-hexopyranosyl)-3-(cyanomethy1)indole 29, in which the methyl uronate grouping of the antibiotics is present at a lower oxidation level.
Two structurally related indole nucleoside antibiotics, neosidomycin (5) and SF-2140 (3) have been synthesised; it is confirmed that the structure initially proposed for neosidomycin must be revised.In 1979, a novel N-glycosyl indole antibiotic, neosidomycin, was isolated from a strain of Streptomyces hygroscopicus. The relative stereostructure (1) was assigned to neosidomycin, principally on the basis of the n.m.r. data of its di-0-acetyl derivative (2), with the assumption that both (1) and (2) adopt 4c1(D) chair conformations in solution. More recently, the antiviral indole nucleoside SF-2140 has been isolated from an Actinomadura species, and, on the basis of degradative, spectroscopic, and X-ray data, assigned structure (3).2 In order to reconcile the crystallographic and 1H n.m.r. data, which included in particular large coupling constants J 1 j ,2! and J41ax,51, the authors postulated that, in solution, SF-2140 (3) and its di-0-acetyl derivative (4) adopt twist-boat conformations, as illustrated in (4') for the derivative. Since the
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