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2024-12-14 09:21本頁(yè)面
【正文】 droxy acids were prepared using the literature method with modifications from the corresponding amino acids valine, leucine, and phenylalanine. Improved yields were obtained by slowly simultaneous addition of three fold excess of sodium nitrite and 1 tnol/L H2SO4. In the preparation of ahydroxy acid methyl esters from ahydroxy acids following the procedure described by Vigneron, a low yield (45%) was obtained It was found that much better results (yield 82%) could be obtained by esterifying ahydroxy acids with methanolthionyl first attempt to convert (S)2hydroxy3methylbutanoic acid methyl ester to the corresponding (R)1,1diphenyl2mercapto3methyllbutanol is as the following: (S)2Hydroxy3methylbutanoic acid methyl ester was treated with excess of phenylmagnesium bromide to give (S)1,1diphenyl3methyl1,2butanediol, which was then mesylated to obtain (S)1,1diphenyl3methyl2(methanesulfonyloxy)lbutanol. Unfortunately, conversion of (S)1,1diphenyl3methyl2(methanesulfonyloxy)lbutanol to the corresponding thioester by reacting with potassium thioacetate under Sn2 reaction conditions can be achieved neither in DMF at 2060 nor in refluxing toluene in the presence of 18crown6 as catalyst. When (S)1l,ldiphenyl3methyl2(methane sulfonyloxy)lbutanol was refluxed with thioacetic acid in pyridine, an optical active epoxide (R)2,2diphenyl 3isopropyloxirane was obtained. Then we tried to convert (S)1,1diphenyl3methyll,2butanediol to the thioester by reacting with PPh3, DEAD and thioacetic acid (the Mitsunobu reaction), but we failed either, probably due to the steric hindrance around the reaction actually successful synthesis is as described below: ahydroxy acid methyl esters was mesylated and treated with KSCOCH3 in DMF to give thioester, this was than treated with phenyl magnesium bromide to gave the target pound Bmercaptoalcohols. The enantiomeric excesses of pmercaptoalcohols can be determined by 1H NMR as their (S)mandeloyl derivatives.(S)2amino3phenylpropanelthiol hydrochloride was synthesized from LPhenylalanine. LPhenylalanine was reduced to the amino alcohol (S)2amino3phenylpropanol. Protection of the amino group using tertbutyl pyrocarbonate gave (S)2tert butoxycarbonylamino3phenylpropanelol, which was then Omesylated to give (S)2tertbutoxycarbonylamino3phenylpropyl methanesulfonate. The mesylate was treated with potassium thioacetate in DMF to give lacetylthio2tertbutoxycarbonylamino3phenylpropane. The acetyl group was then removed by tre
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