Structures of minor components of the validamycin complex.
complicated oligosaccharides using NMRspectroscopy have developed quite remarkably. The structure of validamycin G (VM-G),43 the most recently discovered congener was established by making use of these techniques. Wehave now used NMRto reinvestigated the position of the glycosidic linkage of the minor components which had remained obscure. The results were first disclosed in a patent application,53 though without experimental data. Here we discussed the structures of the minor components with experimental results. To elucidate the unidentified positions of the glucosidic linkage by *H NMRspectroscopy, VM-B~ F were acetylated with acetic anhydride and pyridine to give the corresponding peracetyl derivatives. The chemical shifts of 1-H and l'-H of the peracetates, recognized in the region of 3.2~3.6 ppm, indicate that the imino group is not acetylated. Therefore, these peracetates must be dodeca-O-acetyl validamycin B (Ac-
Stereoselective synthesis of (+)-valienamine starting from the naturally abundant (−)-shikimic acid
Abstract A stereoselective synthesis of the pharmaceutically useful pseudo-aminosugar (+)-valienamine 1 is described. Epoxide 2 was first prepared via four steps in 79.7% overall yield starting from the naturally abundant (−)-shikimic acid. Epoxide 2 was then converted into the vicinal dihydroxyl compound 3 in 96% yield via a highly regio- and stereoselective water-mediated epoxide opening. Compound 3 was transformed into compound 4 in 86% yield over two steps via ester-reduction and benzylation of the three hydroxyl groups. Compound 4 was converted into azido compound 5 in 90% yield via an S N 2-type nucleophilic substitution of the OMs leaving group with sodium azide. Ruthenium-catalyzed stereoselective dihydroxylation of compound 5 afforded dihydroxyl compound 6 in 91% yield. Compound 6 was transformed into compound 7 in 92% yield via selective mono-acetylation of the less-hindered hydroxyl group. Dehydration of tertiary alcohol 7 via an acid-mediated elimination furnished olefinic compound 8 in 85% yield. Finally, compound 8 was converted into the title compound 1 in 91% yield over two steps via deprotection and Lindlar-catalyst-promoted highly selective hydrogenation of the azido group (N 3 ) in the presence of a double bond. (+)-Valienamine 1 was thus synthesized starting from the naturally abundant (−)-shikimic acid via 13 steps in 38.3% total yield.
Studies on validamycins, new antibiotics. II. Production and biological properties of validamycins A and B.
Streptomyces sp., strain No. T-7545 was found to produce new antibiotics, validamycins A and B that are effective for the control of sheath blight of rice plants. The validamycins exhibit no in vitro activity. A taxonomic study of strain No. T-7545 was carried out and it was characterized as follows: It forms gray to gray and yellow aerial mycelium, bright yellow to yellow ocher vegetative mycelium and faint, brownish yellow diffusible pigment, good growth and development of abundant aerial mycelium with the formation of coiled chains of spores at 25-45°C, and black moist areas in the aerial mycelium on certain media. As a result of comparison of strain No. T-7545 with known species, the name Streptomyces hygroscopicus WAKSMAN et HENRICI, 1948 var. limoneus nov. var. is proposed.