Carbon-13 nuclear magnetic resonance spectra of carbohydrate oxirane derivatives

Enhancing the utility of 1JCH coupling constants in structural studies through optimized DFT analysis

High accuracy for DFT-predicted ¹J_CH-couplings can be achieved without ad hoc corrections or empirical scaling by careful selection of the DFT method utilized for geometry optimization and J-coupling calculations.

An efficient route to thioglycosides with the 2,3-anhydro-d-ribo stereochemistry

An improved route for the synthesis of p-tolyl 2,3-anhydro-5-O-benzoyl-1-thio-beta-D-ribofuranoside and its alpha anomer, which are important intermediates in the synthesis of alpha- and beta-D-arabinofuranosides, has been developed. The products are obtained in six steps from D-xylose in 39% overall yield.

Sensitivity of (1)J[C(1)-H(1)] magnitudes to anomeric stereochemistry in 2,3-anhydro-O-furanosides

The magnitude of the one-bond coupling constant between C(1) and H(1) in 2,3-anhydro-O-furanosides has been shown to be sensitive to the stereochemistry at the anomeric center. A panel of 24 compounds was studied and in cases where the anomeric hydrogen is trans to the epoxide moiety, (1)J[C(1)-H(1)] = 163-168 Hz; and when this hydrogen is cis to the oxirane ring, ((1)J[C(1)-H(1)] = 171-174 Hz. In contrast, for 2,3-anhydro-S-glycosides, the size of the (1)J[C(1)-H(1)] is not sensitive to C(1) stereochemistry. Computational studies on all four methyl 2,3-anhydro-O-furanosides (5-8) demonstrated that (1)J[C(1)-H(1)] was inversely proportional to the length of the C(1)-H(1) bond. A previously reported equation, which relates C(1)-H(1) bond distance and atomic charges to (1)J[C(1)-H(1)] magnitudes, could be used to accurately predict the J values in the alpha-lyxo (5) and beta-ribo (8) isomers. In contrast, with the beta-lyxo (6) and alpha-ribo isomers (7), this equation underestimated the size of these coupling constants by 10-20 Hz.

Diastereoselective addition of amines to vinyl sulfone modified carbohydrates: a highly flexible methodology for the synthesis of new classes of deoxyaminosugars

Methyl 2,3-dideoxy-4,6-O-(phenylmethylene)-3-C-phenylsulfonyl-alpha- D-erythro-hex-2-enopyranoside (5 alpha) and methyl 2,3-dideoxy-4,6-O-(phenylmethylene)-3-C-phenylsulfonyl- beta-D-erythro-hex-2-enopyranoside (5 beta) have been subjected to Michael addition reaction with various amines to develop a new methodology for the synthesis of new classes of aminosugars. Compound 5 alpha reacted with primary amines to generate gluco- derivatives, but secondary amines produced both gluco- (major) and manno- (minor) isomers. Compound 5 beta, on the other hand, produced only gluco- isomers with both primary and secondary amines. The stereochemical course of addition of some of the amines to 5 alpha and 5 beta are significantly different from that of the addition of amines to 3-nitroenopyranoses. The present route to the syntheses of various aminosugars with gluco- configurations from 5 alpha and 5 beta constitutes a novel method for the introduction of N-monoalkylated and N,N-dialkylated amines to the C-2 carbon of pyranoses in equatorial configurations.

2,3'-anhydrosucrose

Alkaline hydrolysis of alpha-D-glucopyranosyl 3,4-anhydro-beta-D-ribo-hexulofuranoside (1) involves participation of HO-2 and leads to 2,3'-anhydrosucrose (2). The structure of 2 was assigned on the basis of the n.m.r. and mass spectra of its hexa-acetate 3 and confirmed by the formation from 2 of the 6,6'-di-(4) and 6,1',6'-tri-O-trityl (5) derivatives, the 4,6-O-isopropylidene derivative (6), and 2,3':3,4-dianhydro-galacto-sucrose, isolated as the tetra-acetate 7. The structure of 7 was confirmed by its conversion into the 4'-O-tosyl-6,1',6'-O-trityl derivative 14 and by unambiguous synthesis from 6.