Studies on quinones. XII. Cycloketalization of michael adducts from hydroxyquinones

The reaction of 2-hydroxy-3-(1-phenyl-3-oxobutyl)-1,4-naphthoquinone ( 1 ) with either acidic methanol or a mixture of trimethyl orthoformate, methanol and ammonium chloride resulted in the formation of the p-quinonic cycloketals: trans- and cis-4-phenyl-2-methyl-2-methoxy-3,4-dihydro-2H-naphtho[2,3-b]pyran-5,10-dione ( 2a,2b ). Cyclization of the Michael adducts 6, 10 and 11 , which are structurally related to 1 , with trimethyl orthoformate-methanol-ammonium chloride gave the corresponding p-quinonic cycloketals 7, 12 and 13 . The structures of the regioisomers 2a and 2b are proposed based on the spectral properties of compound 7 and by analysis of its proton nmr spectra.     

Studies on pyrazines. 35. An improved synthesis of bromopyrazines from hydroxypyrazines

The synthesis of bromopyrazines from hydroxypyrazines was successfully effected by the procedure via trimethylsilyloxypyrazines, the sequence of which proceeds under mild conditions and does not require the isolation of intermediate.     

Spectral investigations on melanterite mineral from France.

EPR, Optical and IR spectral studies on a naturally occurring mineral melanterite are carried out at room temperature. EPR studies indicate the presence of Cu(II) ion in tetragonally distorted octahedral site and hyperfine lines could not be resolved due to higher concentration of the paramagnetic impurity in the mineral. Optical absorption spectrum is a characteristic of Fe(II) and Cu(II) ions. Crystal field parameters are evaluated. IR spectrum confirms the presence of water and sulphate ions.     

Studies on Natural Products from Cuban Plants. Alkaloids from Tabernaemontana citrifolia

A detailed study of the alkaloids from Tabernaemontana citrifolia, a species growing in Cuba is presented. Thirteen alkaloids were isolated and characterized. One of these, (?)-19-oxovoacristine ( 7 ), is a new compound isolated for the first lime from a natural source.     

Effect of frequency on the deposition of microcrystalline silicon from tetrachlorosilane in low-pressure r.f. plasmas

The efficiency of reduction of silicon tetrachloride and the rate of deposition of Si in a low-pressure r.f. plasma was investigated at two frequencies (0.4 and 27 MHz) as a function of position with regard to the rf coil, pressure, and time of deposition. At 27 MHz the decomposition efficiency of silicon tetrachloride and the deposition rate of Si are about three times higher than at 0.4 MHz.     

Phospholipase C from Bacillus cereus. Action on some artificial lecithins.

The hydrolysis by phospholipase C from B. cereus of several lecithins of different fatty acyl chain length was examined. The enzyme showed significant activity towards mono-molecularly dispersed short chain lecithins and the reaction obeyed normal Michaelis-Menten kinetics. Rate vs. substrate concentration curves obtained with dihexanoyl-, diheptanoyl- and dioctanoyllecithins showed marked discontinuities in the region of the known critical micelle concentrations for these substrates and distinctly higher rates were obtained just above these levels. Using these three lecithins at levels below their respective critical micelle concentrations, rate increases were noted if the reactions were allowed to proceed to a sufficiently great extent. The presence of deoxycholate in the reaction system had little or no effect on the rate of enzyme-catalysed hydrolysis of lecithins of fatty acyl chain length less than or equal to Cbeta, but for fatty acyl chain lengths greater than C10, significant rate increases occurred. The pH profile for the enzyme activity was also examined.     

内南五味子化学成分的研究

从内南五味子的茎藤中分得七个化合物, 经波谱和X衍射分析, 其中五广系一类新型的螺环衍生物木脂素, 分别定名为内南五味子素(3), 内南五味子素乙(4), 丙(5),J(6)及异内南五味子素(7), 另外两个已知化合物为南五味子素和β-谷甾醇。     

山苍子油化学成分的气相色谱-质谱分析

山苍子为樟科木姜子属植物山鸡椒Litsea cubeba(Lour.)Pers.,广布我国南部省区[1].山苍子具有温中散寒、行气止痛等功效,可用于胃寒呕逆、脘腹冷痛、寒疝腹痛、寒湿郁滞等[2].其鲜果实提取的挥发油(山苍子油)有特殊的清香气,具显著的抗菌、祛痰、抗心律失常等作用[1].山苍子油为香料工业的重要原料,也是合成紫罗兰酮的主要原料[3].为了充分利用这一资源,贵州省在紫云县建立了近万亩的山苍子种植基地,2000年秋季第一次挂果.我们用气相色谱-质谱对贵州省紫云县的山苍子油进行分析研究,以便了解紫云县山苍子的质量情况,为进一步合理开发黔产山苍子提供科学依据.     

Crocins from Crocus sativus L. in the Management of Hyperglycemia. In Vivo Evidence from Zebrafish

Diabetes mellitus is a disease characterized by persistent high blood glucose levels and accompanied by impaired metabolic pathways. In this study, we used zebrafish to investigate the effect of crocins isolated from Crocus sativus L., on the control of glucose levels and pancreatic β-cells. Embryos were exposed to an aqueous solution of crocins and whole embryo glucose levels were measured at 48 h post-treatment. We showed that the application of crocins reduces zebrafish embryo glucose levels and enhances insulin expression. We also examined whether crocins are implicated in the metabolic pathway of gluconeogenesis. We showed that following a single application of crocins and glucose level reduction, the expression of phosphoenolpyruvate carboxykinase 1 (pck1), a key gene involved in glucose metabolism, is increased. We propose a putative role for the crocins in glucose metabolism and insulin management.