Homo-C-nucleoside analogs IV. Synthesis of 4-(2,5-anhydro-D-altro-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole homo-C-nucleoside. CD assignment of the absolute configuration of the carbon bridge.
Dehydrative cyclization of 4-(D-altro-pentitol-1-yl)2-phenyl-2H-1,2,3-triazole in basic medium with one moler equivalent of p-toluene sulfonyl chloride in pyridine solution gave the homo-C-nucleoside 4-(2,5-anhydro-D-altro-1-yl)-2-phenyl-2H-1,2,3-triazole. The structure and anomeric configuration was determined by acylation, nuclear magnetic resonance (NMR), and mass spectroscopy. The stereochemistry at the carbon bridge of homo-C-nucleoside 2-phenyl-2H-1,2,3-triazoles was determined by circular dichroism (CD) spectroscopy.
Circular dichroism as a reliable tool for anomeric assignment of glycosyl-2-phenyl-2H-1,2,3-triazole C-nucleoside analogs. A rule for prediction of their anomeric configuration.
The circular dichroism (CD) of a series of acyclic C-nucleoside analogs; 4-(pentahydroxypentyl-1-yl)-2-phenyl-2H-1,2,3-triazoles [1-5] and 4-(D-glycero-D-gulo)-2-phenyl-2H-1,2,3-triazole 6, are reported. A correlation between the sign of the Cotton effect at the maximal UV absorption and the absolute configuration of the carbon atom alpha- to the triazole base moiety is reported. The CD of anomeric 4-(alpha,beta-D-arabinofuranosyl)- and 4-(alpha,beta-D-arabinopyranosyl)-2-phenyl-2H-1,2,3-triazole C-nucleosides are reported. The assignment of the anomeric configuration of C-glycosyl-2-phenyl-2H-1,2,3-triazoles from their CD spectra was found to be a simple method that relies on comparison of the sign of the Cotton effect at the maximal UV absorption and the absolute configuration of the anomeric carbon atom. A correlation between the anomeric configuration and the sign of the Cotton effect at the maximal UV absorption is deduced and generalized as a rule for prediction of the anomeric configuration of C-glycosyl-2-phenyl-2H-1,2,3-triazoles. Nuclear Overhauser effect and 13C NMR spectra supported the CD assignment rule.
Highly enantio- and diastereoselective synthesis of β-methyl-γ-monofluoromethyl-substituted alcohols.
Enanatiopure β-methyl-γ-monofluoromethyl alcohols were prepared from the allylic alkylation between fluorobis(phenylsulfonyl)methane with Morita-Baylis-Hillman carbonates. The reaction was catalyzed by using the Cinchona alkaloid derivative, (DHQD)(2)AQN. The origin of the stereoselectivity was verified by DFT methods. Calculated geometries and relative energies of various transition states strongly support the observed stereoselectivity.