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A stereocontrolled cyclisation of suitably substituted indole derivatives can be explained by the revised Pictet-Spengler reaction mechanism. 相似文献
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Both (±)-17α-hydroxytacamonine (3) and its 17β-isomer (4) were synthesized in two steps (one-pot) from aldehyde mixture 5/6 via the cyanohydrin reaction. NMR spectral characterization of isomer 3 revealed it to be unidentical with natural 17-hydroxytacamonine, whereas spectral data of isomer 4 were in agreement with those published for the natural isomer. The configuration at C-17 was confirmed by NOE difference spectroscopy. 相似文献
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Mass spectra of phloroglucinol derivatives recently isolated from African Dryopteris species are presented. Phloroglucides with n-valeryl side chain were found in these ferns for the first time. In the mass spectra they show strong peaks corresponding to loss of propene (C3H6) produced by McLafferty rearrangement, as shown in model compounds. Aside of the rottleron change (discussed formerly) this must be considered in order to avoid wrong interpretation, particularly when mass spectra are used to analyse mixtures of homologues, as usually present in the plants. If valeryl side chains are present other methods must be used therefore to measure the amount or show the absence of lower homologues with acetyl side chains. 相似文献
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The synthesis of aldehyde intermediates suitable for the preparation of indole alkaloids of the tacamine ( 1 ) type is described. The four possible aldehydes 4–7 were prepared from methyl 5-ethylnicotinate ( 8 ) in a few simple steps using a base-catalyzed epimerization as the final step (Schemes 1 and 2). The key aldehyde 4 , which is an analogue of the important vincamine intermediate 3 (‘Oppolzer's aldehyde’), was finally converted into the indole alkaloid (±)-apotacamine ( 21 ). 相似文献
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The C(12b)-C(2)-C(3) stereochemical relationship in several racemic 1,2,3,4,6,7,12,12b-octahydro-3-methoxycarbonylindolo [2,3-a]quinolizine derivatives has been determined by 13C NMR spectral analysis. The proper shift assignment was confirmed by recording the spectra of selectively deuterated derivatives. The shifts of specific carbons are found to be conformationally diagnostic. The C(12b)-C(2)-C(3) stereochemical relationship in indolo[2,3-a]quinolizines obtained by selective alkaline decarboalkoxylative cyclization of partially hydrogenated 1-[2-(3-indolyl)ethyl]3,5-dimethoxycarbonylpyridine derivatives is discussed. 相似文献
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The heat capacity of an isotopically enriched (98.3%) 62152Sm metal specimen has been measured. Because the nuclear contribution to Cp is absent in an even-even isotope, the electronic specific heat, CE = 13.5 T mJ/mole·K2, could be determined with higher accuracy (± 2%) than before. 相似文献
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