排序方式: 共有23条查询结果,搜索用时 31 毫秒
1.
Desmond A. Young Daneel Ferreira David G. Roux 《Journal of polymer science. Part A, Polymer chemistry》1986,24(5):835-849
The structure and stereochemistry of four synthetic “angular” tetraflavanoid-condensed tannin derivatives are examined by high-resolution variable temperature 1H NMR. spectroscopy, and hence correlated with their dynamic behavior. Three “angular” oligomers exist as stable rotational isomers at ambient temperatures, thus contrasting with the mobility about their interflavanoid bonds of most natural profisetinidin “trimeric” and “tetrameric” homologs. A “linear” tetraflavanoid analog results from one of these regioselectively controlled condensations. 相似文献
2.
Theoretical calculation of electronic circular dichroism (ECD) of the rotationally restricted 3,8'-biflavonoid (+)-morelloflavone using time dependent density functional theory (TDDFT), performed at 298 K at B3LYP-SCRF/6-31G*//B3LYP/6-31G* level with COSMO model, permitted unequivocal assignment of its 2R,3S absolute configuration. The experimentally observed Cotton effect (CE) around 290 nm is contributed by the acetophenone pi --> pi* transition of the ABC-flavanone moiety and the electronic transition within the DEF-flavone moiety, while another diagnostic positive CE around 350 nm is attributable to the electronic interaction between the ABC-flavanone moiety and the DEF-flavone moiety, as well as the electronic transition within the DEF-flavone moiety. The remarkable differences of the calculated ECD of its two rotamers indicate that the rotational restrictions significantly affect the ECD of 3,8'-biflavonoids. Empirical ECD rules derived from monomeric flavonoids may not be applicable to configurational assignment of complex 3,8'-biflavonoids. This study has provided new insights in interpreting the experimentally observed ECD spectra of this class of compounds. 相似文献
3.
Microbial metabolism of the cancer chemopreventive agent, curcumin [(1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione] (1) with Pichia anomala (ATCC 20170) yielded four major metabolites, 5-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)heptan-3-one (2), 5-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl)heptan-3-one (3), 1,7-bis(4-hydroxy-3-methoxyphenyl)heptan-3,5-diol (4), 5-hydroxy-1,7-bis(4-hydroxyphenyl)heptane-3-one (5) and two minor products, 1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)heptane-3,5-diol (6) and 1,7-bis(4-hydroxyphenyl)heptane-3,5-diol (7). The structures of compounds 2-5 were established on the basis of spectroscopic data. Compounds 6 and 7 were assigned tentative structures. 相似文献
4.
5.
Micha Glesk Marta K. Dudek Peter Kinkade Evelyn C. S. Santos Vitold B. Glinski Daneel Ferreira Ewa Seweryn Sawomir Ka
mierski Joao B. Calixto Jan A. Glinski 《Molecules (Basel, Switzerland)》2022,27(9)
Echimidine is the main pyrrolizidine alkaloid of Echium plantagineum L., a plant domesticated in many countries. Because of echimidine’s toxicity, this alkaloid has become a target of the European Food Safety Authority regulations, especially in regard to honey contamination. In this study, we determined by NMR spectroscopy that the main HPLC peak purified from zinc reduced plant extract with an MS [M + H]+ signal at m/z 398 corresponding to echimidine (1), and in fact also represents an isomeric echihumiline (2). A third isomer present in the smallest amount and barely resolved by HPLC from co-eluting (1) and (2) was identified as hydroxymyoscorpine (3). Before the zinc reduction, alkaloids (1) and (2) were present mostly (90%) in the form of an N-oxide, which formed a single peak in HPLC. This is the first report of finding echihumiline and hydroxymyoscorpine in E. plantagineum. Retroanalysis of our samples of E. plantagineum collected in New Zealand, Argentina and the USA confirmed similar co-occurrence of the three isomeric alkaloids. In rat hepatocyte primary culture cells, the alkaloids at 3 to 300 µg/mL caused concentration-dependent inhibition of hepatocyte viability with mean IC50 values ranging from 9.26 to 14.14 µg/mL. Our discovery revealed that under standard HPLC acidic conditions, echimidine co-elutes with its isomers, echihumiline and to a lesser degree with hydroxymyoscorpine, obscuring real alkaloidal composition, which may have implications for human toxicity. 相似文献
6.
Hua-Dong Chen Yuan-Qing Ding Sheng-Ping Yang Xing-Cong Li Xu-Jie Wang Hai-Yan Zhang Daneel Ferreira Jian-Min Yue 《Tetrahedron》2012,68(30):6054-6058
Morusalbanol A (1), a neuro-protective Diels–Alder adduct with a new carbon skeleton, was isolated from the bark of Morus alba. Compound 1 showed evidence of interesting astropisomerism, and resulted in the absence of a number of key proton and carbon signals in the NMR spectra. Its structure was thus elucidated by spectroscopic analysis of its peracetylated derivative (2) and its absolute configuration established as 1S,3S,4R,5S via experimental and calculated ECD spectra of 1. In a neuro-protective assay, morusalbanol A (1) significantly attenuated the H2O2-induced cell damage in a dose-dependent manner. 相似文献
7.
Herath W Mikell JR Hale AL Ferreira D Khan IA 《Chemical & pharmaceutical bulletin》2008,56(4):418-422
5,7-Dihydroxyflavone (chrysin) (1) when fermented with fungal cultures, Aspergillus alliaceous (ATCC 10060), Beauveria bassiana (ATCC 13144) and Absidia glauco (ATCC 22752) gave mainly 4'-hydroxychrysin (4), chrysin 7-O-beta-D-4-O-methylglucopyranoside (5) and chrysin 7-sulfate (6), respectively. Mucore ramannianus (ATCC 9628), however, transformed chrysin into six metabolites: 4'-hydroxy-3'-methoxychrysin (chrysoeriol) (7), 4'-hydroxychrysin (apigenin) (4) 3',4'-dihydroxychrysin (luteolin) (8), 3'-methoxychrysin 4'-O-alpha-D-6-deoxyallopyranoside (9), chrysin 4'-O-alpha-D-6-deoxyallopyranoside (10), and luteolin 3'-sulfate (11). Cultures of A. alliaceous (ATCC 10060) and B. bassiana (ATCC 13144) metabolized 5-hydroxyflavone (2) into 5,4'-dihydroxyflavone (12) and 4'-hydroxyflavone 5-O-beta-D-4-O-methylglucopyranoside (13), respectively. 6-Hydroxyflavone (3) was transformed into 6-hydroxyflavanone (14), flavone 3-O-beta-D-4-O-methylglucopyranoside (15) and (+/-)-flavanone 6-O-beta-D-4-O-methylglucopyranoside (16) by cultures of Beauveria bassiana (ATCC 13144). The structures of the metabolic products were elucidated by means of spectroscopic data. The significance of the metabolites as antioxidants in relation to their structure is briefly discussed. 相似文献
8.
Oligomeric proanthocyanidins: naturally occurring O-heterocycles 总被引:1,自引:0,他引:1
This review covers the flavan-3-ols (catechins), flavan-4-ols/flavan-3,4-diols (leucoanthocyanidins), A-type proanthocyanidins, B-type proanthocyanidins including the procyanidins, prodelphinidins, propelargonidins, proteracacinidins, promelacacinidins, procassinidins, probutinidins, and non-proanthocyanidins with flavan-3-ol constituent units. Newly isolated proanthocyanidins, structure elucidation, syntheses, HPLC/MS analysis, NMR/ conformational analysis, and the effects of proanthocyanidins on human nutrition and health are reported. The literature from January 1999 to December 2001 is reviewed, and 130 references are cited. 相似文献
9.
Several microorganisms showed the ability to transform the harman alkaloids, harmaline (1), harmalol (2) and harman (5). Harmaline (1) and harmalol (2) were converted by Rhodotorula rubra ATCC 20129 into the tryptamines, 2-acetyl-3-(2-acetamidoethyl)-7-methoxyindole (3) and 2-acetyl-3-(2-acetamidoethyl)-7-hydroxyindole (4), respectively. Harman (5) was biotransformed by Cunninghamella echinulata NRRL 3655 into 6-hydroxyharman (6) and harman-2-oxide (7). 相似文献
10.
Microbial transformation of xanthohumol using the culture broth of Cunninghamella echinulata NRRL 3655 afforded (2S)-8-[4"-hydroxy-3"-methyl-(2"-Z)-butenyl]-4',7-dihydroxy-5-methoxyflavanone (5) and (2S)-8-[5"-hydroxy-3"-methyl-(2"-E)-butenyl]-4',7-dihydroxy-5-methoxyflavanone (6). Xanthohumol (1) and flavanone 6 as well as (E)-2"-(2"'-hydroxyisopropyl)-dihydrofurano[2",3":4',3']-2',4-dihydroxy-6'-methoxychalcone (2), (2S)-2"-(2"'-hydroxyisopropyl)-dihydrofurano[2",3":7,8]-4'-hydroxy-5-methoxyflavanone (3) obtained with Pichia membranifaciens showed antimalarial activity against Plasmodium falciparum. 相似文献