Synthesis of acetylenic sugars and uronic acids via two-carbon chain extension of d-ribose

Abstract

Treatment of methyl β- d-ribofuranoside with acetone gave methyl 2,3- O-isopropylidene-β- d-ribofuranoside ( 1, 90%), whereas methyl α- d-ribofuranoside gave a mixture (30%) of 1 and methyl 2,3- O-isopropylidene-α- d-ribofuranoside ( 1a). On oxidation, 1 gave methyl 2,3- O-isopropylidene-β- d- ribo-pentodialdo-1,4-furanoside ( 2), whereas no similar product was obtained on oxidation of 1a. Ethynylmagnesium bromide reacted with 2 in dry tetrahydrofuran to give a 1:1 mixture (95%) of methyl 6,7-dideoxy-2,3- O-isopropylidene-β- d- allo- ( 3) and -α- l- talo-hept-6-ynofuranoside ( 4). Ozonolysis of 3 and 4 in dichloromethane gave the corresponding d- allo- and l- talo-uronic acids, characterized as their methyl esters ( 5 and 6) and 5- O-formyl methyl esters ( 5a and 6a). Ozonolysis in methanol gave a mixture of the free uronic acid and the methyl ester, and only a small proportion of the 5- O-formyl methyl ester. Malonic acid reacted with 2 to give methyl 5,6-dideoxy-2,3- O-isopropylidene-β- d- ribo- trans-hept-5-enofuranosiduronic acid ( 7).