Glucitol isomerization

Treatment of l,4 3,6-dianhydro-D-glucitol with boron trichloride gives l,6-dichloro-l,6-dideoxy-D-glucitol (20). Although methyl 6-chloro-6-deoxy-a-D-glucopyranoside (isolated as the tribenzoate) could be isolated from the reaction of methyl 3,6-anhydro-a-D-glucopyranoside with boron trichloride (21), the application to the isomeric furanoside derivative led to complex results. 

Michaelis-Menten enzymatic isomerization only two of the six sugar forms are substrates for the enzyme Km values for glucose, fructose, glucitol and mannitol are 0.13, 0.04, 0.4 and >1 m, respectively. 

Sorbitol is D-glucitol. It is a hexahydric alcohol related to mannose and is isomeric with mannitol. 

A new method of D-glucan analysis involves reductive cleavage of permethylated compounds with triethylsilane and trimethylsilyl triflate or boron trifluoride-etherate as catalyst, followed by acetylation, which yields a series of acetylated, methylated 1,5-anhydro-glucitols. A number of isomeric substituted 1,5-anhydro-glucitols were synthesized as references. /3-Glycosyl-... 

A useful strategy for the selective substitution of dianhydroglucitols utilizing a titanium-mediated hydride reduction of l,4 3,6-dianhydro-2,5-di-0-nitro-D-glucitol has appeared. Thus reduction of the latter with titanium(III) borohydride [Ti(BH4)3] affords the monoester 10, and with diisopropyloxytitanium(III) borohydride [( PrO)2TiBH4]the isomeric compound 11 is produced. ... 

Acetonation of 3-0-methyl-D-glucitol affords the isomeric 1,2 5,6-and 2,4 5,6-di-0-isopropylidene derivatives which are differentiated on silica gel layers [hRf 50 and 25, respectively, in benzene-methanol (90 + 10)] with visualization by iodine vapor [85]. The four stereoisomers of l,2 5,6-di-0-trichloroethyUidene-a-D-glucofuranose, which differ in the configuration of the acetal carbons atoms, are resolved on silica gel with ethyl acetate-petroleum ether (b. p. 40—50°) (50 + 50) [86]. Chloroform-acetone (97 + 3) and benzene-ether (90 + 10) have been used to separate mixtures of acylated di-O-isopropylidene-hexitols [87, 88]. 

The isomerically pure l,4 3,6-dianhydro-D-glucitol monoacetates 27 and 28 were available by selective esterification of the diol 25 or selective hydrolysis of the diacetate 26, respectively, with SAM II lipase (a highly selective lipase from Pseudomonas sp.). ... 

---