Alkyl Galactopyranosides: Rotational Population Dependence of the Hydroxymethyl Group on the Aglycon and Its Absolute Configuration and on the Anomeric Configuration
摘要:
The rotational populations of the hydroxymethyl group in chiral and nonchiral alkyl alpha- and beta-galactopyranosides proved, on the basis of circular dichroism (CD) and H-1 NMR data, to be dependent on the structure of the aglycon: the population of the gt and tg rotamers increased and decreased, respectively, as the pK(a) of the bonded alcohol (aglycon) increased, while the population of the gg rotamer remained practically constant. Furthermore, low-temperature CD measurements proved that the most stable rotamer is the gt, and not the tg. In addition, a clear correlation between the rotational populations and the absolute configuration of the chiral aglycon was observed; namely, higher and smaller gt and tg populations were observed for the (S)-alkyl beta-D-galactopyranosides than for their (R)-alkyl beta-D-galactopyranoside counterparts, the opposite behavior being observed for the cl-anomers. The results point to the exo anomeric effect as being responsible for these rotational dependencies, as well as to nonbonding interactions between the aglycon and the chromophore at C6 for those stereoisomers having in their aglycon a bulky substituent syn to the endocyclic oxygen (O5). In addition, the chemical shift differences (Delta delta) of the aglyconic protons of galactosylated chiral alcohols proved to be characteristic of the absolute configuration of the bonded chiral alcohol.
Abstract We describe a general method that permits characterization of 100-pg to 1-ng quantities of sugars. Thus, oligosaccharides are subjected to methanolysis, followed by per- p -bromobenzoylation or pernaphthoylation, and the methylglycoside peresters are separated by high-pressure liquid chromatography. The method is also applicable to amino and acetamido sugars. If required, the separated sugar
Twonovel norlanostane triglycosides, ectyoplasides A (1) and B (2), have been isolated from the methanolic extracts of the Caribbean sponge Ectyoplasiaferox (Raspaliidae, Axinellida). Their structures have been established by extensive application of high-resolution FABMS and two-dimensional NMR techniques, supported by chemical and enzymatic degradation methods. Ectyoplasides A and B have been shown
从加勒比海绵 Ectyoplasiaferox(Raspaliidae,Axinellida)的甲醇提取物中分离出两种新型去甲羊毛脂烷三糖苷,ectyoplasides A (1) 和 B (2)。它们的结构是通过广泛应用高分辨率 FABMS 和二维核磁共振技术建立的,并得到化学和酶促降解方法的支持。Ectyoplasides A 和 B 已被证明具有相同的糖链(由两个 β-半乳糖单元和一个 α-阿拉伯糖单元组成),但它们的苷元部分不同,它们具有在环 A 上具有前所未有的取代模式的去甲三萜骨架。当对各种细胞系进行体外测试时,A 和 B 显示出中等的细胞毒活性
Quinofuracins A–E, Produced by the Fungus <i>Staphylotrichum boninense</i> PF1444, Show p53-Dependent Growth Suppression
Quinofuracins A-E, novel anthraquinone derivatives containing beta-D-galactofuranose that were isolated from the fungus Staphylotrichum boninense PF1444, induced p53-dependent cell death in human tumor cells. The structures of quinofuracins A-E, including absolute configurations, were elucidated by extensive spectroscopic analysis and chemical transformation studies. Quinofuracins were classified into three groups according to the aglycone moieties. 5'-Oxoaverantin was present in quinofuracins A-C, whereas averantin and versicolorin B were identified in quinofuracins D and E, respectively. These quinofuracins induced p53-dependent growth suppression in human glioblastoma LNZTA3 cells.