Synthesis of 5a,5a'-dicarba-d-glucobioses from conformationally restricted carbaglucosyl triflates using SN2-type inversion with carbaglucosyl nucleophiles.

Novel carbohydrate mimics were designed which contain two 5a-carba-d-glucose residues, one each at reducing and nonreducing end, and thus these mimics are 5a,5a'-dicarba-d-glucobioses. Dicarbadisaccharides have attractive features such as stability against endogenous degradative enzymes and being resistant to glycation reactions such as the Maillard reaction. For the synthesis of dicarba-ß-d-isomaltose derivatives, the carbaglucosyl triflate locked in 4C1 conformation was synthesized by protecting with butane-2,3-diacetal group or benzylidene group. Then, 5a,5a'-dicarba-ß-d-maltose and 5a,5a'-dicarba-α,ß-d-trehalose were synthesized by the SN2-type inversion reaction using 4,6-O-benzylidene carbaglucosyl triflate with 4-OH and 1-OH carba-ß-d-glucose derivatives, respectively, and similarly 5a,5a'-dicarba-α-d-isomaltose with 6-OH carba-α-d-glucose derivative.

A recombinant α-(2→3)-sialyltransferase with an extremely broad acceptor substrate specificity from Photobacterium sp. JT-ISH-224 can transfer N-acetylneuraminic acid to inositols.

We confirmed that a recombinant α-(2→3)-sialyltransferase cloned from Photobacterium sp. JT-ISH-224 recognizes inositols having a structure corresponding to the C-3 and C-4 of a galactopyranoside moiety, such as epi-, 1d-chiro, myo-, and muco-inositol, as acceptor substrates, and that the enzyme can transfer N-acetylneuraminic acid (Neu5Ac) from cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-Neu5Ac) to them. After purifying the reaction products, the structures were confirmed by use of NMR spectroscopy and mass spectrometry. From these results, it was clearly shown that the α-(2→3)-sialyltransferase from Photobacterium sp. JT-ISH-224 recognizes acceptor substrates through the cis-diol structure corresponding to the 3- and 4-position of the galactopyranoside moiety.