Abul K.M.S. Kabir

The synthesis of some seven-carbon sugars via the osmylation of olefinic sugars

Abstract The stereochemical outcome of the catalytic osmylation of 6,7-dideoxy-1,2:3,4-di- O -isopropylidene-α- d - galacto -hept-6-enopyranose ( 10 ), 5,6-dideoxy-1,2- O -isopropylidene-α- d - xylo -hex-5-enofuranose, ( E )- and ( Z )-3- O -benzyl-5,6-di-deoxy-1,2- O -isopropylidene-α- d - xylo -hept-5-enofuranose ( 20 and 27 , respectively), methyl ( Z )-3- O -benzyl-5,6-dideoxy-1,2- O -isopropylidene-α- d - xylo -hept-5-enofuranuronate ( 26 ), ( E )-3- O -benzyl-5,6-dideoxy-1,2- O -isopropylidene-α- d - ribo -hept-5-enofuranose, benzyl ( E )- and ( Z )-5,6-dideoxy-2,3- O -isopropylidene-α- d - lyxo -hept-5-enofuranoside ( 46 and 50 , respectively), and methyl [benzyl ( Z )-5,6-di-deoxy-2,3- O -isopropylidene-α- d - lyxo -hept-5-enofuranosid]uronate ( 49 ) has been examined. Such oxidations led to satisfactory syntheses of l - glycero - d - gluco -heptose and the corresponding heptitol (from 20 ), l - glycero - d - gulo -heptitol (from 26 ), d - glycero - d - gluco -heptitol (from 27 ), d - glycero - d - galacto -heptitol (from 10 and 46 ), ( meso )- glycero-gulo -heptitol (from 49 ), and d - glycero - d - manno -heptitol (from 50 ).

A synthesis of l-lyxo-l-altro-nonitol, a new nonitol☆

Abstract Catalytic osmylation of ( E )-6- O -benzyl-7,8-dideoxy-1,2:3,4-di- O -isopropylidene-α- d - glycero - d - galacto -non-7-enopyranose ( 15 ) proceeded with good stereo-selectivity to give a mixture of 6- O -benzyl-1,2:3,4-di- O -isopropylidene-β- l - lyxo - d - galacto -nonopyranose ( 16 ) and the α- d - xylo - d - galacto isomer 17 in the ratio ∼8.5:1. After debenzylation of this mixture, crystalline 1,2:3,4-di- O -isopropylidene-β- l - lyxo - l - galacto -nonopyranose ( 21 ) was isolated and converted in a straight-forward manner into l - lyxo - l - altro -nonitol ( l - lyxo - d - galacto -nonitol) ( 23 ). The ( E )-allylic alcohol 15 can be prepared by way of Wittig olefination of 6- O -benzyl-1,2:3,4-di- O -isopropylidene-α- d - glycero - d - galacto -heptodialdo-1,5-pyranose ( 13 ) with formylmethylenetriphenylphosphorane or (methoxycarbonylmethylene)triphenylphosphorane, followed by appropriate reduction of the enal 14 or conjugate ester 24 .

On the stereochemistry of osmium tetraoxide oxidations of allylic systems used in the synthesis of higher-carbon sugars☆

Abstract The stereochemistry of the major osmylation products of carbohydrate-based allylic alcohols can usually be predicted by application of Kishis empirical rule. In particular, the addition of OsO 4 can be formulated as taking place in the more abundant conformation on the surface anti to a pyranose or furanose ring-oxygen atom located at a stereocentre adjacent to the olefinic linkage. Exceptions to Kishis empirical rule for osmylation are sometimes encountered with conjugated carbonyl compounds.

The synthesis and osmylation of 7,8-dideoxy-1,2:3,4-di-O-isopropylidene-β-l-glycero-d-galacto-oct-7-enopyranose and related studies☆

Abstract A stereocontrolled route to 7,8-dideoxy-1,2:3,4-di- O -isopropylidene-β- l - glycero - d - galacto -oct-7-enopyranose ( 8 ) has been developed from 6,7-anhydro-1,2:3,4-di- O -isopropylidene-β- l - erythro - d - galacto -octopyranose ( 15 ), in which the final and key step involved a facile, reductive elimination on the epoxy-iodide 18 . As predicted by Kishis empirical rule, the major product obtained on catalytic osmylation of either 8 or its 6- O -benzyl derivative 21 possesses the β- l - erythro - d - galacto configuration ( i.e. , 19 or 22 , respectively).

Higher-carbon sugars. Part 2. The synthesis of some decitols via the osmylation of unsaturated precursors

Sharpless epoxidation of (E)-8,9-dideoxy-1,2 : 3,4 : 6,7-tri-O-isopropylidene-α-D-threo-D-galacto-dec-8-enopyranose (3) with di-isopropyl L-(+)-tartrate as the chiral auxiliary furnished a mixture of 8,9anhydro-1,2 : 3,4 : 6,7-tri-O-isopropylidene-β-L-galacto-D-galacto-decopyranose (10)(isolated in 63% yield) and the α-D-ido-galacto isomer (11) in the ratio ∼5 : 1. Base-catalysed hydrolysis of the epoxy alcohol (10) gave, via preferential ring-opening of the Payne-rearrangement product (12), 1,2 : 3,4 : 6,7-tri -O-isopropylidene-α-D-altro-D-galacto-decopyranose (8), which yielded Daltro-D-galacto-decitol (13) following acidic hydrolysis and reduction of the resulting decose. The epoxy alcohol (11) was the principal product obtained on Sharpless epoxidation of the decenopyranose (3) with di-isopropyl D-(–)-tartrate as the chiral auxiliary, and was similarly transformed into L-gluco-D-galacto-decitol (L-galacto-D-gulo-decitol)(16). The same strategy was also used in the synthesis of D-gluco-D-galacto-decitol (L-galacto-L-gulo-decitol)(1) and L-altro-D-galacto-decitol (25) from (E)-8,9-dideoxy-1,2 : 3,4 : 6,7-tri-O-isopropylidene-β-L-threo-D-galacto-dec-8-enopyranose (18).

Higher-carbon sugars. Part 12. The synthesis of new octitols from D-glucose and D-mannose via the osmylation of unsaturated precursors

Catalytic osmylation of methyl (E)-2,3,4-tri-O-benzyl-6,7-dideoxy-α-D-gluco-oct-6-enopyranoside (8) produced a mixture of methyl 2,3,4-tri-O-benzyl-β-L-threo-D-gluco-octopyranoside (9) and the corresponding α-D-threo-D-gluco isomer (10) in the ratio ca. 3:1, respectively. After separation from the mixture as the crystalline triacetate (11), the regenerated triol (9) was transformed into L-threo-L-altro-octitol (L-threo-D-gluco-octitol)(12). Methyl (E)-2,3,4-tri-O-benzyl-6,7-dideoxy-α-D-manno-oct-6-enopyranoside (17) furnished a mixture of methyl 2,3,4-tri-O-benzyl-β-L-threo-D-manno-octopyranoside (18) and the corresponding α-D-ihreo-D-manno isomer (19) on catalytic osmylation. The crystalline hexa-acetate (20) derived from the octopyranoside (18) was subsequently transformed into D-erythro-L-altro-octitol (L-threo-D-manno-octitol)(21). Both osmylation reactions proceed in accordance with Kishis empirical rule. The structural assignments are based on single-crystal X-ray analyses of the acetylated compounds (11) and (20).

Higher-carbon sugars. Part 1. The synthesis of some octose sugars via the osmylation of unsaturated precursors

Titanium-catalysed asymmetric epoxidation of (E)-6,7-dideoxy-1,2:3,4-di-O-isopropylidene-α-D-galacto-oct-6-enopyranose (1) with di-isopropyl L-(+)-tartrate afforded 6,7-anhydro-1,2:3,4-di-O-isopropylidene-β-L-threo-D-galacto-octopyranose (4), which was identified by its conversion on basic hydrolysis into 1,2:3,4-di-O-isopropylidene-α-D-erythro-D-galacto-octopyranose (6)via preferential ring-opening of the Payne-rearrangement product (5) at the terminal position. Oxidation of (1) with m-chloroperbenzoic acid gave principally the isomeric epoxy alcohol (8), which basic hydrolysis similarly transformed into 1,2:3,4-di-O-isopropylidene-β-L-erythro-D-galacto-octopyranose (10). The latter sequence of reactions also yielded 1,2:3,4-di-O-isopropylidene-α-D-threo-D-galacto-octopyranose (3) from (Z)-6,7-dideoxy-1,2:3,4-di-O-isopropylidene-α-D-galacto-oct-6-enopyranose (12). D-erythro-D-galacto-Octitol (7), L-erythro-D-galacto-octitol (11), and D-threo-D-galacto-octitol (16) are accessible from the protected octoses (6), (10), and (3), respectively.