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71.
[formula: see text] Two novel sesterpenes, bilosespens A and B (1 and 2) were isolated from the Red Sea sponge Dysidea cinerea collected in the Dahlak archipelago, Eritrea. The structure of the mixture of the two inseparable compounds was established by spectroscopic analysis, mainly by 1D and 2D NMR measurements. The mixture of bilosespens A and B is cytotoxic to a few human cancer cells. 相似文献
72.
Proton magneticf resonance spectrometry was applied for evaluation of the distribution ratios and apparent extraction constants of tetraalkylammonium and tetraalkylphosphonium salts in two liquid-phase systems. Triethylbenzyl- and tetrabutylammonium chloride in dichloromethane and chlorobenzene, respectively, were shown to be salted out in the presence of aqueous sodium hydroxide solutions. 1H-n.m.r. spectrometry was also used to determine the degree of hydration of quaternary onium salts in two-phase systems. The results were compatible with those obtained by the Karl Fischer method. 相似文献
73.
Six new biogenetically interesting alkylated scalarins, scalardysin-A and B, scalar-herbacin-A and B and the latter's acetates were isolated from . Structures are suggested for the various compounds based on their spectral data. 相似文献
74.
Four PGF derivatives (15S)-PGF2α-11-acetate methyl ester (a), the 18-acetoxy derivative of compound a (a) as well as their two corresponding free carboxylic acids (b) & b) were isolated from a soft-coral and their structure elucidated, mainly on basis of their spectral data. 相似文献
75.
A complete 1H and 13C NMR assignment of one of the latrunculins (B) was accomplished with the aid of 2D NMR COSY and CH shift-correlation experiments. The various H-H Coupling constants have been datermined and a conformation of the macrolide and the tetrahydropyran (THP) ring suggested on basis of the J-values and measured NOE's. The absolute configuration of latrunculin-A() was determined on the grounds of its earlier X-Ray analysis, and a chemical degradation to a known compound. Two novel latrunculins, -C() and -D(), were isolated from the Red Sea sponge and their structures elucidated. Starting with L-cysteine a synthon for the latrunculins has been synthesized. 相似文献
76.
Phosphole sulfide 1 undergoes cycloaddition to give a new 15-phosphasteroid. The 13C-NMR and 2JPC-coupling constants of several compounds prepared similarly are discussed, permitting structure assignment to one of the 7-phosphabicyclo[2.2.1]heptane adduct 5. Thiophosgene reacts with the PS moiety of 1, giving 12 after hydrolysis, through a PS to PO transformation coupled in case of 1 with a proton migration. 相似文献
77.
8-Phosphabicyclo[3.2.1]octanes—III4: The reaction between oxyallyl cations and phosphole derivatives
The reaction of oxyallyl cations with phosphole sulfide as well as phosphole oxides was investigated and was found to give the expected 8-phosphabicyclo[3.2.1]octanic system (2, 4 and 7) apart from other unexpected products (3 and 5). In the case of the phosphole sulfide (1), the oxyallyl cation is believed to react preferentially with the P=S group, rather than the dienic moiety, leading to a P=S to P=O transformation or to a very particular reaction resulting in 5. This occurs through an intermediate (j) in which a C=S group reacts in a [2 + 4] cycloaddition with the phosphole as a diene. The structure and stereochemistry of the various products were established by the aid of their spectral data in conjunction with spectral data of some related compounds. A formal PhPO elimination is believed to occur through an intermediate phosphinate resulting from Bayer-Villiger like oxidation, which then loses the [PhPO2] group.Phosphole sulfide (1), previously found to react as a dienophile, was shown to enter a [2 + 4] cycloaddition as a diene with powerful dienophiles like 4-methyl-1,2,4-triazoline-3,5-dione (10). 相似文献
78.
Yoel Tikochinsky 《International Journal of Theoretical Physics》1994,33(8):1599-1609
Using the algebraic properties of Poisson brackets, we extend the three-dimensional brackets (for a single free particle) to conform to the demands of special relativity. This yields, in an essentially unique way, the manifestly covariant extension [x
,p
v]=+p
p
v/m
2
c
2. Position and time then become fully dynamical variables expressible in terms of the canonical conjugateq
i andp
i and the time parameter asx
i =q
i +p
i(q ·p)/m
2c2 andt = +E(q ·p)/m
2c4. In the quantized version, the length associated with a particle of massm is shown to be an integral multiple of the Compton wavelength
C =/mc. 相似文献
79.
Three novel nitrogenous macrolides designated salarin A and B (1 and 2) and tulearin A (3) were isolated from the Madagascar Fascaplysinopsis sp. sponge. The structures of the compounds were elucidated by interpretation of MS and 1D and 2D NMR spectra. Both salarins carry an acetylcarbamate moiety, and in addition, 1 contains a triacylamine group and 2 a methoxymethylketone lactam. Tulearin A carries the naturally rare carbamate ester. The compounds were found to be toxic to brine shrimp larvae, and salarin A and tulearin A were also cytotoxic to leukemia cells. 相似文献
80.
Two closely related lipodepsipeptides, taumycins A and B (1 and 2) have been isolated from the Madagascar sponge Fascaplysinopsis sp. The two compounds have the same 12-membered oxodepsipeptide ring system in common. Both were toxic to brine shrimp larvae, and taumycin A (1 microM), but not taumycin B, inhibited growth of the human UT-7 leukemic cell line. The structure of the two compounds, likely to be derived from microorganisms, was established by MS and 1D and 2D NMR data. 相似文献