Susumu Honda

Stereochemistry of the methoxymercuration of glycal acetates

Abstract The methoxymercuration of the acetates of d -glucal, d -galactal, l -arabinal and d -xylal was studied by n.m.r. spectroscopy, and by stereoselective demercuration with thiourea, as well as by reductive demercuration with sodium borohydride. It is considered to be a trans -addition to the double bond to yield isomeric methyl glycosides having mercury attatched to C-2. The proportion of diaxial to diequatorial addition is strongly affected by the protecting groups at C-4 and C-5.

Fluorimetric determination of reducing sugars with ethylenediamine sulfate

Abstract A new simple method of fluorimetric determination of reducing sugars is proposed. In phosphate buffer (pH 8.00) containing more than a 10-fold molar amount of ethylenediamine sulfate, reducing sugars (4 ·1O -3 -4 ·10 -1 μmol) may be determined without interference from glycosides or neutral polysaccharides.

Equimolar oxymercuration of D-glucal triacetate with mercuric perchlorate and its application to the synthesis of 2′-deoxy disaccharides

Abstract A search for appropriate reaction conditions for the equimolar methoxymercuration of D -glucal triacetate was made by using various mercuric salts, bases, and reaction solvents. Under optimum conditions with mercuric perchlorate, sym -collidine, and acetonitrile, D -glucal triacetate underwent methoxymercuration with an equimolar amount of methanol to afford methyl 3,4,6-tri- O -acetyl-2-deoxy-2-perchloratomercuri-β- D -glucopyranoside ( 1 , 26%) and its α- D - manno isomer ( 2 , 49%). Equimolar oxymercuration of D -glucal triacetate with partially protected sugars, followed by subsequent demercuration of the products with sodium borohydride, afforded α- and β-linked 2′-deoxy disaccharide derivatives in moderate yields. The partially protected sugars used were 1,2,3,4-tetra- O -acetyl-β- D -glucopyranose and 1,2:3,4-di- O -isopropylidene-α- D -galactopyranose, and the corresponding products were O -(3,4,6-tri- O -acetyl-2-deoxy-α- D - arabino -hexopyranosyl)-(1→6)-1,2,3,4-tetra- O -acetyl- D -glucopyranose( 4 , 23%) and its β-linked isomer ( 5 , 11%) from the former, and O -(3,4,6-tri- O -acetyl-2-deoxy-α- D - arabino -hexapyranosyl)-(1→6)-1,2:3,4-di- O -isopropylidene-α- D -galactopyranose ( 9 , 29%) and its β-linked isomer ( 10 , 10%) from the latter. Deacetylation of these 2′-deoxy disaccharides was effected with methanolic sodium methoxide, but deacetonation was unsuccessful owing to simultaneous cleavage of the glycosidic linkage.

Hydroxy- and acetoxy-mercuration of D-glucal triacetate

Abstract Hydroxy- and acetoxy-mercuration of D -glucal triacetate ( 1 ) afforded 2-acetoxymercuri-3,4,6-tri- O -acetyl-2-deoxy- D -glucose ( 2 ) and 2-acetoxymercuri-1,3,4,6-tetra- O -acetyl-2-deoxy-α- D -glucopyranose ( 3 ), respectively. On demercuration with sodium borohydride, compound 2 gave at first the acyclic 4,6-di- O -acetyl- D - erythro -hex-2-enose ( 4 ), which was further reduced to the corresponding hex-2-enitol derivative ( 5 ). Demercuration of 3 with borohydride gave a mixture of 1 and 1,3,4,6-tetra- O -acetyl-2-deoxy-α- D - arabino -hexopyranose ( 6 ). On the other hand, demercuration of 2 and 3 with thiourea yielded 4 and 1 , respectively. The reaction mechanisms of both oxymercurations are also discussed.

Selective micro determination of unconjugated uronic acids by fluorescence reactions with ethylenediamine sulfate

Abstract A simple method for the spectrofluorimetric determination of uronic acids is proposed. The fluorescence at 328 (excitation) and 405 nm (emission) formed by heating sample solutions in acetate buffer containing large amounts of ethylenediamine sulfate, can be used to determine 1.0·10 -2 –3.0·10 -2 or 4.0·10 -2 –4.0·10 -1 μmole of unconjugated uronic acids accurately, without interference from other carbohydrate materials, especially uronides.

Periodate oxidation analysis of carbohydrates : Part I. Spectrophotometr1c determination of glyoxal in dialdehyde fragments formed from glycosides with 2,4-dinitrophenylhydrazine

Abstract A simple procedure for the determination of glyoxal in dialdehyde fragments, formed from glycosides by periodate oxidation, is proposed. By heating sample solutions prepared by dilution of reaction mixtures for periodate oxidation, with an aqueous dimethylsulfoxide solution of 2,4-dinitrophenylhydrazine hydrochloride. followed by addition of an aqueous ethanolic solution of potassium hydroxide, intense color with an absorption maximum at 576 nm developed. The spectrophotoinetric method based on this color reaction makes it possible to determine selectively 1·10 −2 –2·10 −1 μmole amounts of conjugated glyoxal without a prior liberation process. Data for glyoxal content obtained by this procedure are discussed in relation to overoxidation.

Iodinolysis of C-2 mercurated hexose derivatives

Abstract Reaction of the C-2 mercurated methyl hexopyranoside acetates 1–3 with an excess of iodine resulted in nearly quantitative replacement of mercury by iodine with retention and inversion of configuration at C-2. Similar replacement was observed with 2-acetoxymercuri-3,4,6-tri- O -acetyl-2-deoxy-α- d -glucopyranose ( 4 ). In the iodinolysis of 2-acetoxymercuri-1,3,4,6-tetra- O -acetyl-2-deoxy-α- d -glucopyranose ( 5 ) in methanol, however, replacement at C-2 was accompanied to a considerable extent by solvolysis of the 1-acetoxyl group, and a mixture of 1,2- trans isomers of methyl 3,4,6-tri- O -acetyl-2-deoxy-2-iodo-hexopyranosides having the d - gluco and d - manno configurations was obtained, together with 1,3,4,6-tetra- O -acetyl-2-deoxy-2-iodo-α- d -mannopyranose.