L. Hough

On the automated analysis of neutral monosaccharides in glycoproteins and polysaccharides

Abstract An improved method for the automated, quantitative analysis of glycoproteins and polysaccharides for neutral monosaccharide components has been developed, based on the ion-exchange chromatography at pH 7 of sugar-borate complexes. The destruction of sugars during acid hydrolysis has been investigated, and a variety of methods for the neutralization of hydrolysates have been evaluated.

Some further ring-opening reaction of methyl 4,6-O-benzylidene-2,3-dideoxy-2,3-epimino-α-D-allopyranoside and its derivatives

Modifications have been made to the preparation of methyl 4,6- O-benzylidene-2,3-dideoxy-2,3-epimino-α-D-allopyranoside from derivatives of 2-amino-2-deoxy-D-glucose, which permit it to be prepared in high yield and on a large scale. Further, ring-opening reactions of the epimine and its N-substituted derivatives have been studied with halide ion under neutral and acidic conditions. It has been found that anomalous, diequatorial ring-opening occurs when the free epimine is treated with ammonium halides (except the fluoride) in N,N-dimethylformamide, but, with its N-substituted derivatives, diaxial ring-opening predominates, although diequatorial ring-opening is significant in many cases. Under acidic conditions, the free epimine undergoes hydrolysis of the benzylidene group, without rupture of the epimine ring, but its N-substituted derivatives undergo predominant, diaxial ring-opening before hydrolysis of the benzylidene group. Ring-opening reactions of the N-methanesulphonyl and N-acetyl derivatives with azide occur trans-diaxially and trans-diequatorially, respectively.

Sucrochemistry : Part I. New derivatives of sucrose prepared from the 6,6′-DI-O-tosyl and the octa-O-mesyl derivatives

Abstract Treatment of 6,6′di- O -tosylsucrose hexa-acetate with sodium methoxide gave 3,6;3′,6′-dianhydrosucrose. Benzoylation of 6,6′-di- O -tosylsucrose with cooling gave the hexabenzoate ( 6 ) in high yield, whereas at room temperature significant quantities of 6,6′-dichloro-6,6′-dideoxysucrose hexabenzoate ( 7 ) and a monochloro-monodeoxy-mono- O -tosylsucrose hexabenzoate were also obtained. The 6,6′-dichloro derivative 7 was obtained from 6 by nucleophilic substitution using pyridinium hydrochloride. Treatment of 6 with iodide gave the 6,6′-di-iodo derivative 9 which on hydrogenation was converted into 6,6′-dideoxysucrose hexabenzaote ( 10 ). Treatment of 9 with silver fluoride in pyridine afforded the 5,5′-diene. Substitution reactions on 6 with azide and thiocyanate gave 6,6′-diazido and 6,6′-dithiocyanato derivatives of sucrose as their hexabenzoates. Octa- O -mesylsucrose underwent selective substitution reactions with various nucleophiles. With iodide, it gave the 6,6′-dideoxy-6,6′-di-iodo derivative 15 which was identical with that prepared by mesylation of 6,6′-di- O -tosylsucrose followed by treatment with iodide. Reduction of 15 gave 6,6′-dideoxysucrose hexamethanesulphonate, which was synthesized also from the dideoxy hexabenzoate 10 by de-esterification and mesylation. 5,5′-Dieno, 6,6′di-azido, and 6,6′dithiocyanato derivatives of sucrose hexamethanesulphonate were prepared. A triazido-sucrose pentamethanesulphonate was prepared from the octamethanesulphonate.

Sucrochemistry : Part VI. Further reactions of 6,6′-DI-O-tosylsucrose and a comparison of the reactivity at the 6 and 6′ positions

Abstract Reaction of 6,6′-di- O -tosylsucrose hexa-acetate ( 1 ) with sodium chloride in hexamethylphosphoric triamide gave a mixture containing preponderantly the hexa-acetates of 6,6′-dichloro-6,6′-dideoxysucrose ( 2 ) and 6-chloro-6-deoxy-6′- O -tosyl-sucrose ( 3 ). Reaction of 3 with sodium benzoate in (Me 2 N) 3 PO gave the 6-chloro-6-deoxy-6′- O -benzoyl derivative 4 . Subsequent O -de-esterification afforded syrupy 6-chloro-6-deoxysucrose ( 5 ), which gave a crystalline heptamethanesulphonate. The chloro groups in the heptabenzoate 7 and the hexa-acetate 2 were replaced by azide in (Me 2 N) 3 PO to give the corresponding derivatives of 6-azido-6-deoxysucrose ( 12 ) and 6,6′-diazido-6,6′-dideoxysucrose ( 8 ), respectively. O -De-esterification of the hexa-acetates 2 and 8 yielded the parent 6,6′-dichloride 6 and 6,6′-diazide 9 , respectively. 6,6′-Di- O -tosylsucrose hexabenzoate ( 10 ) reacted with sodium bromide in (Me 2 N) 3 PO to give the 6,6′-dibromide 11 , in high yield, which afforded 6-deoxy-β- D - xylo -hex-5-enopyranosyl 6′-deoxy-β- D - threo -hex-5′-enofuranoside hexabenzoate on treatment with silver fluoride in pyridine.

A new synthesis of a 2,3-epimino-α-D-allopyranoside

Abstract Methyl 4, 6-aO-benzylidene-2,3-dideoxy-2,3-epimino-α- D -allopyranoside has been prepared from methyl 2-benzamido-4,6-aO-benzylidene-2-deoxy-3-aO-methanesulphonyl-α- D -glucopyranoside, by the action of lithium aluminium hydride in tetrahydrofuran. On treatment of the same compound with ethanolic sodium ethoxide, the allo-imine was again the main product, together with a small amount of methyl 2-benzamido-4,6-O-benzylidene-α- D -glucopyranoside. This is in contrast to the predominant formation of oxazolines and similar derivatives from related compounds in the β- D -glucopyranose series, observed by other authors. These reactions are rationalised on the basis of conformational analysis.

Nucleophilic replacement reactions of sulphonates : Part I. The preparation of derivatives of 4,6-diamino-4,6-dideoxy-D-glucose and -D-galactose

Abstract The nucleophilic displacement reactions of some 4,6-disulphonates of methyl α- D -glucopyranoside and methyl α- D -galactopyranoside have been studied by using sodium azide in N , N -dimethylformamide. Displacement occurs at both positions by a bimolecular mechanism, giving the corresponding 4,6-diazides with inversion of configuration at C-4. The azides have been reduced to derivatives of 4,6-diamino-4,6-dideoxy- D -glucose and - D -galactose.

Synthesis of the indolizidine alkaloid swainsonine from d-glucose

Abstract Since the stereochemistry of the alkaloid exactly matches that of 3-amino-3-deoxy- d -mannose, the latter compound is an ideal chiron for the synthesis of the former. Selective tosylation of methyl 3-benzyloxycarbonylamino-3-deoxy-α- d -mannopyranoside, followed by removal of the benzyloxycarbonyl group and cyclisation, afforded the 3,6-imine which was converted into its benzyloxycarbonyl derivative. Hydrolysis of the glycosidic group then afforded 3,6-benzyloxycarbonylimino-3,6-dideoxy- d -mannose. The attempted addition of a C 2 unit at C-1 by the Wittig or the Wadsworth—Emmons—Horner reaction either failed to give the required product or was followed by Michael addition of one of the hydroxyl groups to the newly formed double-bond. 2,4,5-Tri- O -acetyl-3,6-benzyloxycarbonylimino-3,6-dideoxy- aldehydo - d -mannose was prepared via the diethyl dithioacetal and condensed with ethoxycarbonylmethylenetriphenylphosphorane to give the Wittig adduct in good yield, which, on catalytic reduction, underwent hydrogenation of the double bond, loss of the benzyloxycarbonyl group, and attack of the released amino group on either the terminal ethoxycarbonyl group or the 2- O -acetyl group to give a mixture of the required cyclic lactam and the N -acetyl derivative. Reduction of the lactam with the borane—dimethyl sulphide complex afforded swainsonine triacetate, from which the parent alkaloid was obtained.

Derivatives of β-D-fructofuranosyl α-D-galactopyranoside

Abstract De-etherification of 6,6′-di- O -tritylsucrose hexa-acetate ( 2 ) with boiling, aqueous acetic acid caused 4→6 acetyl migration and gave a syrupy hexa-acetate 14 , characterised as the 4,6′-dimethanesulphonate 15 . Reaction of 2,3,3′4′,6-penta- O -acetylsucrose ( 5 ) with trityl chloride in pyridine gave a mixture containing the 1′,6′-diether 6 the 6′-ether 9 , confirming the lower reactivity of HO-1′ to tritylation. Subsequent mesylation, detritylation, acetylation afforded the corresponding 4-methanesulphonate 8 1′,4-dimethanesulphonate 11 . Reaction of these sulphonates with benzoate, azide, bromide, and chloride anions afforded derivatives of β- D -fructofuranosyl α- D -galactopyranoside ( 29 ) by inversion of configuration at C-4. Treatment of the 4,6′-diol 14 the 1,′4,6′-triol 5 , the 4-hydroxy 1′,6′-diether 6 with sulphuryl chloride effected replacement of the free hydroxyl groups and gave the corresponding, crystalline chlorodeoxy derivatives. The same 4-chloro-4-deoxy derivative was isolated when the 4-hydroxy-1′,6′-diether 6 was treated with mesyl chloride in N,N -dimethylformamide.

The preparation of 4,6-dichloro-4,6-dideoxy-α-d-galactopyranosyl 6-chloro-6-deoxy-,β-d-fructofuranoside and the conversion of chlorinated derivatives into anhydrides☆

Abstract Under carefully controlled conditions, sucrose is converted by selective reaction with sulphuryl chloride into either 6-chloro-6-deoxy-α- d -glucopyranosyl 6-chloro-6-deoxy-β- d -fructofuranoside or 4,6-dichloro-4,6-dideoxy-α- d -galactopyranosyl 6-chloro-6-deoxy-β- d -fructofuranoside, which could be isolated without recourse to chromatography. Treatment of the dichloride with sodium methoxide gave 3,6-anhydro-β- d -glucopyranosyl, 3,6-anhydro-β- d -fructofuranoside in high yield. In contrast, 4,6-dichloro-4,6-dideoxy-α- d -galactopyranosyl 6-chloro-6-deoxy-β- d -fructofuranoside gave, in two distinct stages, 3,6-anhydro-4-chloro-4-deoxy-α- d -galactopyranosyl 6-chloro-6-deoxy-β- d -fructofuranoside and 3,6-anhydro-4-chloro-4-deoxy-α- d -galactopyranosyl 3,6-anhydro-β- d -fructofuranoside. The structures of these products were ascertained by 1 H-n.m.r. and mass spectrometry.

Syntheses of cellobiosyl, maltosyl, and lactosyl derivatives of asparagine

Abstract Three N -glycosylasparagines have been synthesised, namely, 1- N -(4- L -aspartyl)-4- O -β- D -glucopyranosyl-β- D -glucopyranosylamine, 1- N -(4- L -aspartyl)-4- O -α- D -glucopyranosyl-β- D -glucopyranosylamine, and 1- N -(4- L -aspartyl)-4- O -β- D -galactopyranosyl-β- D -glucopyranosylamine. They were obtained from the polyacetates of cellobiose, maltose, and lactose, via the 1-bromides, 1-azides, and then the 1-amines, followed by condensation with 1-benzyl N -benzyloxycarbonyl- L -aspartate. Two coupling reagents, dicyclohexylcarbodiimide and 2-ethoxy- N -ethoxycarbonyl-1,2-dihydroquinoline are compared. The latter has the distinct advantage of ease of purification of the products by facilitating the removal of by-products. The mass spectra of the fully protected N -glycosylasparagines are discussed.