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-
Biosynthesis and Biological Activity of Carbasugars
The first synthesis of carbasugars, compounds in which the ring oxygen of a monosaccharide had been replaced by a methylene moiety, was described in 1966 by Professor G. E. McCasland’s group. Seven years later, the first true natural carbasugar (5a-carba-R-D-galactopyranose) was isolated from a fermentation broth of Streptomyces sp. MA-4145. In the following decades, the chemistry and biology of carbasugars have been extensively studied. Most of these compounds show interesting biological properties, especially enzymatic inhibitory activities, and, in consequence, an important number of analogues have also been prepared in the search for improved biological activities. The aim of this review is to give coverage on the progress made in two important aspects of these compounds: the elucidation of their biosynthesis and the consideration of their biological properties, including the extensively studied carbapyranoses as well as the much less studied carbafuranoses.
Melanocins A, B and C, new melanin synthesis inhibitors produced by Eupenicillium shearii. I. Taxonomy, fermentation, isolation and biological properties.
New melanin synthesis inhibitors, melanocins A, B and C, were isolated from the fermentation broth and mycelium extract of Eupenicillium shearii F80695. Melanocin A, an isocyanide compound, inhibited mushroom tyrosinase and melanin biosynthesis of B16 melanoma cells with IC50 value of 9.0 nM and MIC value of 0.9 microM, respectively. Melanocin A also inhibited growth of Streptomyces bikiniensis. While, the structurally very related but non-isocyanide compounds melanocins B and C did not show inhibitory activity in these assays. Melanocins A, B and C showed potent antioxidant activity with scavenging activity of DPPH radical and superoxide anion radical.