Galacto-configuration

Substitution reactions of 36 with nucleophilic acetate ions, followed by acetylation, furnished two carba-sugar pentaacetates of the a-DL-ido (38 31 % yield) and a-DL-galacto configurations (19 10%). The reactions seemed to involve formation of an intermediary 2,3-cyclic acetoxonium ion. ... 

The phosphonium salt X derived from 1,2 3,A-di-0-isopropylidene-a-D-galactopyranose was readily prepared ( ), and the ylide derived from it was condensed effectively with both aliphatic and aromatic aldehydes. The products all had the a-D-galacto configuration, and the aliphatic aldehydes afforded only the Z-isomers. The less constrained permethylated phosphonium salt XI was also prepared, and... 

J. Hill, L. Hough, and A. C. Richardson, Replacement of methanesulphonyloxy groups Conversion of the D-gluco into the D-galacto configuration, Proc. Chem. Soc. (1963) 346-347. 

Another approach for determination of the absolute configuration of the monosaccharide components69 involves their interaction with radioactive potassium cyanide and conversion of the products into a mixture of heptonamides. Isotopic-dilution experiments showed the presence of D-gfi/cero-L-manno-heptonamide, thus establishing the D-galacto configuration of the starting hexose. 

J. Yoshimura and M. Matsuzawa, Stereoselective synthesis of methyl 4-C-acetyl-6-deoxy-2,3-O-methylene-D-galactonate and -D-gluconate. Determination of the D-galacto configuration of methyl eurekanate by synthesis, Carbohydr. Res. S5 C1 (1980). 

Among nucleoside glycosyl monophosphates, the primary derivatives include cytidine (N-acetyl neuraminic monophosphate) (CMP-NeuAc),51 in which the n-glycero-fi-n-galacto configuration of the monosaccharide group has been confirmed,52 and the analogous derivative of 3-deoxy-D-manno-2-octulosonic acid.53,54... 

Transition from the D-gluco to the D-galacto configuration occurs through enzymic epimerization at C-4 of the hexosyl group in glycosyl nucleotides. Such reactions were observed for UDP-Glc,14,102-104 UDP-GlcNAc,44,105-107... 

Amino-3,6-dideoxyhexoses having the d-gluco and d-galacto configurations were identified as constituents of several lipopolysaccharides. In extracts of Xanthomonas campestris, conversion of 7a into a dTDP-3-... 

In the reaction of benzyl 3-azido-5-0-benzoyl-3,6-dideoxy-a-L-talofuranoside (4) with (diethylamino)sulfur trifluoride (DAST) the anomeric alkoxyl group migrated to the C-2 position and a fluorine atom entered into C-l from the P-side to give the 2-benzyl ether 5 having P-l-galacto configuration [101]. Methyl 2-0-benzoyl-5-0-... 

Substitution of a six-membered stannylene derivative involving the primary position always occurs at that position. Various 6-0-benzyl derivatives of d-gluco and d-galacto configuration have been prepared by this method in good yields [54, 135]. Treatment of allyl 2-acetamido-3-0-benzyl-2-deoxy-4,6-0-dibutylstannylene-a-D-galactopyranoside with benzyl bromide in the presence of tetrabutylammonium iodide furnished 75 % of the 6-benzyl ether [141]. 

Selective tritylation of methyl oc-L-rhamnopyranoside yielded 57% of the 3-0-trityl derivative, together with 1 % of the 2-0- and 3 % of 4-0-trityl isomers. For methyl P-L-rhamnopyranoside, 34% of the 3-trityl and 17% of the 4-trityl ether were obtained [315]. Similarly, the 3,6-ditrityl ether is the major product of ditrityl-ation of methyl and benzyl a-D-mannopyranosides [316]. The corresponding a-D-glucopyranosides yielded the 2,6-di-O-trityl derivative, whereas both the 2,6- and 3,6-ditrityl ethers were isolated in the case of [Pg.237]

In 1987, a second isomer of this class was found in OPS of P. aeruginosa 012 and thought to have the v>-glycero-L-galacto configuration.30 The same, or mistakenly inferred as the same, sugar was reported to be present in a... 

Sn-2 reactivity is dramatically reduced at the primary C(6) position of galacto-configured pyranoses, relative to their gluco isomers. The low reactivity is widely attributed to dipole-dipole interactions in the transition structure, but ab initio calculations on model compounds suggest that the energy attributable to such interactions is not sufficient to explain the reactivity difference,9 whereas rotameric populations and reaction path curvature are.10... 

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