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Vicenistatin, an antitumor antibiotic isolated from Streptomyces halstedii, is a unique 20-membered macrocyclic lactam with a novel aminosugar vicenisamine. The vicenistatin biosynthetic gene cluster (vin) spanning approximately 64 kbp was cloned and sequenced. The cluster contains putative genes for the aglycon biosynthesis including four modular polyketide synthases (PKSs), glutamate mutase, acyl CoA-ligase, and AMP-ligase. Also found in the cluster are genes of NDP-hexose 4,6-dehydratase and aminotransferase for vicenisamine biosynthesis. For the functional confirmation of the cluster, a putative glycosyltransferase gene product, VinC, was heterologously expressed, and the vicenisamine transfer reaction to the aglycon was chemically proved. A unique feature of the vicenistatin PKS is that the loading module contains only an acyl carrier protein domain, in contrast to other known PKS-loading modules containing certain activation domains. Activation of the starter acyl group by separate polypeptides is postulated as well. 相似文献
33.
Shibuya H Agusta A Ohashi K Maehara S Simanjuntak P 《Chemical & pharmaceutical bulletin》2005,53(7):866-867
The microbial transformation of (+)-catechin (1) and (-)-epicatechin (2) by endophytic fungi isolated from a tea plant was investigated. It was found that the endophytic filamentous fungus Diaporthe sp. transformed them (1, 2) into the 3,4-cis-dihydroxyflavan derivatives, (+)-(2R,3S,4S)-3,4,5,7,3',4'-hexahydroxyflavan (3) and (-)-(2R,3R,4R)-3,4,5,7,3',4'-hexahydroxyflavan (7), respectively, whereas (-)-catechin (ent-1) and (+)-epicatechin (ent-2) with a 2S-phenyl group resisted the biooxidation. 相似文献
34.
Miyoji Hanaoka Shingo Yasuda Kazuyoshi Nagami Keiko Okajima Takeshi Imanishi 《Tetrahedron letters》1979,20(39):3749-3752
Irradiation of the berberinephenolbetaines (, , and ) effected valence tautomerization to give the 8,14-cycloberbines (, , and ), the aziridine derivatives, in high yield. The 8,14-cycloberbines were efficiently converted to the spirobenzylisoquinolines by regioselective C bond cleavage. 相似文献
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The paper reports results of experiments to estimate the mortality of ocean bottom dwellers, ostracoda, against underwater shock wave exposures. This study is motivated to verify the possible survival of ocean bottom dwellers, foraminifera, from the devastating underwater shock waves induced mass extinction of marine creatures which took place at giant asteroid impact events. Ocean bottom dwellers under study were ostracoda, the replacement of foraminifera, we readily sampled from ocean bottoms. An analogue experiment was performed on a laboratory scale to estimate the domain and boundary of over-pressures at which marine creatures’ mortality occurs. Ostracods were exposed to underwater shock waves generated by the explosion of 100mg PETN pellets in a chamber at shock over-pressures ranging up to 44MPa. Pressure histories were measured simultaneously on 113 samples. We found that bottom dwellers were distinctively killed against overpressures of 12MPa and this value is much higher than the usual shock over-pressure threshold value for marine-creatures having lungs and balloons. 相似文献
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Shunsuke Kotani Masaya Ito Hirono Nozaki Masaharu Sugiura Masamichi Ogasawara Makoto Nakajima 《Tetrahedron letters》2013
An application of a hypervalent silicon complex, generated from a chiral phosphine oxide catalyst and silicon tetrachloride, to the enantioselective organocatalytic Morita–Baylis–Hillman reaction is described. A chloride anion liberated from the hypervalent silicon complex smoothly generated a γ-chloro silyl enol ether that subsequently reacted with an aldehyde to afford the Baylis–Hillman adducts in good yields and with good enantioselectivities. 相似文献
40.
Abstract The primary structure of an elicitor-active oligosaccharide, LN-3, prepared from partially hydrolyzed algal laminaran was determined by means of the analyses of glycosyl-linkage, fragments by acetolysis, and glycosyl-sequence. The elicitor-active oligosaccharide, LN-3, is a pyridylaminated hepta-β-d-glucoside which was shown to have the following linear structure: β-d-Glcp(1→6)-β-d-Glcp(1→3)-β-d-Glcp(1→3)-β-d-Glcp(1→3)-β-d-Glcp(1→6)-β-d-Glcp(1→3)-Glc-PA. 相似文献