Stereospecific Photoredox-Catalyzed Vinylations to Functionalized Alkenes and C-Glycosides**

We report an efficient radical-mediated C−C coupling through photoredox-catalyzed reactions of 4-alkyl-dihydropyridines (DHPs) and vinylbenziodoxol(on)es (VBX, VBO). This transition-metal-free and mild photocatalytic method has excellent functional group tolerance and affords vinylated products in good yields, with complete retention of the alkene configuration. The utility of the methodology is demonstrated by the diastereoselective synthesis of C-vinyl glycosides. Preliminary mechanistic studies suggest that the C−C bond formation is stereospecific and proceeds through a concerted radical coupling transition state.     

Formation of C-Glycosides by Ferrier Reaction

Peracetylated glycals were treated with terminal alkyne derivatives under Lewis acid catalysis to result in the formation of the pure α- or β- anomerically substituted hex-2-enopyranosides carrying 2(E)-halogenated olefins.     

Titanocene-Catalyzed Reduction of Lactones to Lactols

A convenient method for the conversion of lactones to lactols is described. The hydrosilylation to lactols is carried out via air-stable titanocene difluoride or a titanocene diphenoxide precatalyst using inexpensive polymethylhydrosiloxane (PMHS) as the stoichiometric reductant. These procedures have been demonstrated with a variety of substrates and proceed in good to excellent yield.     

Further Highly Oxygenated Guaiane Lactones from the South China Sea Gorgonian Menella sp.

Four new highly oxygenated guaiane lactones, 1‐epimenverin B ( 1 ), menverin F ( 2 ), 1‐deoxymenverin F ( 3 ), and menverin G ( 4 ), together with the two known related analogues menverins B ( 5 ) and C ( 6 ), were isolated from the South China Sea gorgonian Menella sp. Their structures and relative configuration were elucidated by analysis of spectroscopic data and by comparison with those of known related compounds.     

苯乙酮碳苷化合物快原子轰击质谱的特征及碎裂机理的研究

采用正离子快原子轰击质谱(PFABMS)和联动扫描谱[1](B/E和B2/E)相结合,研究了六个苯乙酮-β-D-吡喃糖碳苷的裂解规律.不仅得到了各化合物的质子化分子离子峰[M+H+],而且通过联动扫描谱证实了此类化合物糖基序列特征离子的归宿,为研究此类碳苷化合物的结构提供了依据.     

In Vitro Liver Metabolism of Six Flavonoid C-Glycosides

Several medical plants belonging to the genera Passiflora, Viola, and Crataegus accumulate flavonoid C-glycosides, which likely contribute to their efficacy. Information regarding their phase I and II metabolism in the liver are lacking. Thus, in vitro liver metabolism of orientin, isoorientin, schaftoside, isoschaftoside, vitexin, and isovitexin, all of which accumulated in Passiflora incarnata L., was investigated by incubation in subcellular systems with human liver microsomes and human liver S9 fraction. All metabolite profiles were comprehensively characterized using HPLC-DAD and UHPLC–MS/MS analysis. Mono-glycosylic flavones of the luteolin-type orientin and isoorientin showed a broad range of mono-glucuronidated and mono-sulfated metabolites, whereas for mono-glycosylic flavones of the apigenin-type vitexin and isovitexin, only mono-glucuronidates could be detected. For di-glycosylic flavones of the apigenin-type schaftosid and isoschaftosid, no phase I or II metabolites were identified. The main metabolite of isoorientin was isolated using solid-phase extraction and prep. HPLC-DAD and identified as isoorientin-3′-O-α-glucuronide by NMR analysis. A second isolated glucuronide was assigned as isoorientin 4′-O-α-glucuronide. These findings indicate that vitexin and isovitexin are metabolized preferentially by uridine 5′-diphospho glucuronosyltransferases (UGTs) in the liver. As only orientin and isoorientin showed mono-sulfated and mono-glucuronidated metabolites, the dihydroxy group in 3′,4′-position may be essential for additional sulfation by sulfotransferases (SULTs) in the liver. The diglycosylic flavones schaftoside and isoschaftoside are likely not accepted as substrates of the used liver enzymes under the chosen conditions.     

Stereoselective Synthesis of C-Glycosides by Suzuki Cross-coupling Reaction

Carbohydrates and their conjugates have been recognized to play a wide variety of metabolic roles in numerous biological processes.[1] Various modified sugars and analogues have been recently synthesized for further investigation of glycosidase reactions and for the development of specific glycosidase inhibitors.[2] As one of the most important carbohydrate mimics, C-glycosides have attracted great attention due to their stability to chemical or enzymatic hydrolysis of the glycosidic linkage. A number of methodologies for the preparation of C-glycosides have been extensively investigated.[3] We have recently reported the syntheses of novel C-glycosyl amino acids and amino-C-disaccharides possessing a ketose form via the stereoselective 1,3-dipolar cycloaddition of exo-methylenesugars (1) and nitrones.[4,5] As a continuation of our research on the synthesis of C-glycosides using exo-methylenesugar as the precursor, we wish to describe here a stereoselective synthesis of C-glycosides by Suzuki cross-coupling reaction.     

Convenient Synthesis of Bicyclic Lactones Related to the Trichothecenes

Short and convenient synthesis of bicyclic lactones (1) and (2), important intermediates in trichothecene synthesis is described.