摘要:

The main synthetic reactions o f carbohydrates a t the anomeric center involve ionic processes. commonly cationic processes for glycosylations and anionic processes for C-branching reactions. The use of homolytic or radical reactions has emerged in the last decade for the synthesis of complex molecules. These developments are of great interest for synthetic purposes and for the study of stereoelectronic effects at the anomeric center of carbohydrates. This short review summarizes the principal results of radical transformations at C-1 of aldoses.

ISSN:0732-8303    

DOI:10.1080/07328308808058900

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A convenient route for the regiosetective substitution of the primary hydroxyls of sucrose is reported. The application of Mitsunobu's procedure with phthatimide yields. without chromatographic separations, di- cr triphtha-timido derivatives substituted at the 6.6′ and 1′ positions of sucross. Simutta-neous formation of a 3′,4′ epoxide in thetagatoconfiguration is observed. The corresponding aminodeoxysucroses are obtained by hydrazinolysis of those derivatives.

ISSN:0732-8303    

DOI:10.1080/07328308808058901

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Theerythroandthreochiral C4-N, phenylsulfenimines (3) and (4), prepared from the (2S,3R)-methyl diol obtained in fermenting baker's yeast from cinnamaldehyde, were convertedviareaction with BrMgCH2CH˭CHCH3and BrMgCH2CH˭CHCH3/ZnCl2, respectively, into the isomeria C8-Nadducts (5)2, bearing relative stereochemistry at position 4 and 5 depending upon the reagent used. Ozonolysis of the terminal vinyl group of theN-trifluoroacetyl derivatives yielded, through the different addition experiments, the eight isomeric 2-C-methyl-2,3,6-trideoxy-3-amino-L-hexose derivatives (6) - (13).

ISSN:0732-8303    

DOI:10.1080/07328308808058902

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Readily available 6-substituted 3,4-di-O-acetyl-1,2-glycals have been converted to their 2-O-acetyl-3,4-dideoxy-hex-3-enopyranosides by a stereoselective alkoxypalladation followed by addition of sodium cyanoborohydride which effected a stereoselective and regioselective allylic rearrangement with chirality transfer. Using this reaction methyl 2,6-di-O-acetyl-3,4-dideoxy-α-D-erythro-hex-3-enopyranoside (13). ethyl 2,6-di-O-acetyl-3-4-dideoxy-α-D-erythro-hex-3-enopyranoside (15), β-(trimethylsilyl) ethyl 2,6-di-O-acetyl-3,4,-dideoxy-α-D-erythro-hex-3-enopyranoside (17), methyl 2-O-acetyl-3,4-dideoxy-α-D-erythro-hex-3-enopyranoside (19), methyl 2-O-acetyl-6-azido-3,4,6-trideoxy-α-D-erythro-hex-3-enopyranoside (21), methyl 2-O-acetyl-6-O-methyl-3,4,-dideoxy-α-D-erythro-hex-3-enopyranostde (20), methyl 2,6-di-O-acetyl-3,4,-dideoxy-α-D-threo-hex-3-enopyranoside (22), methyl 4-O-acetyl-6-cyano-2,3,6-trideoxy-α-D-erythro-hex-2-enopyranoside (24), methyl 4-O-acetyl-2,3-dideoxy-α-D-glycero-pent-2-enopyranoside (25), and methyl-4-O-acetyl-2,3,6-trideoxy-α-L-erythro-hex-2-enopyranostde (26) were synthesized in excellent yield from their corresponding 1,2-glycals. In this reaction it was found that both sodium cyanoborohydride and a coordinating group at C-6 were necessary to effect the regioselective allylic rearrangement. These rearrangements can be rationalized on the basis that following transalkoxypalladation the resulting 2,3-palladium π complex is reduced to a Pd(0) complex by sodium cyanoborohydride which then undergoes allylic rearrangement assisted by coordination of the group at C-6 to control the regioselectivity.

ISSN:0732-8303    

DOI:10.1080/07328308808058903

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Fusion reactions ofp-nitrophenol with acetates of chito-biose, chitotriose, chitotetraose, and chitopentaose under autocatalytic conditions gave the correspondingp-nitrophenyl chitooligosides acetates in acceptable yields. CompleteO-deacetylation of these acetates was attained by treatment with sodium methoxide in methanol under reflux in the case of the latter two, and at room temperature with the former two.

ISSN:0732-8303    

DOI:10.1080/07328308808058904

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Penta-N,O-acetylvaliolamine (11), a derivative of microbial α-D-glucosidase inhibitor, was prepared from the chiral azido-containing cyclohexene derivative derived fromD-glucose. Novel rearrangement of the C-C double bond accompanying reduction of the azido group vas a key step for the preparation.

ISSN:0732-8303    

DOI:10.1080/07328308808058905

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Benzyl 2,5-di-O-(tert-bstvldimethvl)silvl-3-O-triflvl-β-D-ribofsranoside (13) underwent triflyl migration uponO-desilylation with triethylammonium hydrogen fluoride in tetrahydrofuran affording benzyl 2-O-triflyl-β-D-ribo-furanoside (7) in ca. 5% yield, together with three other products, benzyl 3-O-triflyl-β-D-ribofuranoside (17), benzyl 2-O-(tert-butyldimethyl)silvl-3-O-triflyl-β-D-ribo-furanoside (18) and benzyl 3-deoxy-β-D-glvceropento-furanos-2-uloside (16). In order to confirm the triflyl migration, a series of reactions were performed.

ISSN:0732-8303    

DOI:10.1080/07328308808058906

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A modified Kiliani-Fischer reaction is used to prepare multigram quantities of [1-13C]-enriched glucose and mannose which are converted chemically or enzymatically into other labeled monosaccharides. The simplest conversion is the synthesis of labeled fructose from labeled glucose using commercially available immobilized glucose isomerase. The equilibrium for this reaction provides a 1:l mixture of glucose and fructose which can be separated by chromatography. The equilibrium can be shifted toward fructose by treating the reaction with germanate ion. [1-13C]Mannose can be converted into more useful sugars using a modification of the Lobry de Bruyn-Alberda van Ekenstein transformation. In this reaction, D-[1-13C]mannose is treated with an aqueous solution of dilute alkali and phenylboronate to form a mixture of labeled fructose, mannose and glucose. Fructose can be converted to a mixture of methyl fructofuranosides by using trifluoroacetic acid in methanol. [2-13C]Dihydroxyacetone can be prepared from methyl D-[2-13C]fructose by treatment with periodate followed by reduction with borohydride and acid hydrolysis.

ISSN:0732-8303    

DOI:10.1080/07328308808058907

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A facile procedure is presented for the synthesis of (E)-1-(3′-hydroxy-2′-furanyl)-3-(3″-hydroxy-4″-methoxyphenyl)-2- propen-1-one (6). Galactosylisomaltol (1) was condensed with isovanillin (2) under strong alkaline conditions at 25 [ddot]C to form (E)-1-(3′-O-β-D-galactopyranosyloxy-2′-furanyl)-3-(3″- hydroxy-4″-methoxyphenyl)-2-propen-1-one (4). (E)-1-(3′-hydroxy-2′-furanyl)-3-(3″-hydroxy-4″-methoxyphenyl)-2-propen-1-one (6) was obtained by acid hydrolysis of 4 in a 53.9% yield. This hetero-cyclic 2-propen-1-one was characterized on the basis of spectral data (IR and1H NMR), physicochemical properties, and conversion to a mono-O-acetyl derivative.

ISSN:0732-8303    

DOI:10.1080/07328308808058908

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The reduction of two peracetylated aryl 2-deoxy-α-D-C-hex-2-enopyranosides by several reagents is described. The steric course of the reaction is discussed.

ISSN:0732-8303    

DOI:10.1080/07328308808058909

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor