We have established a facile and efficient protocol for the preparative-scale synthesis of various compound libraries related to lactosaminoglycans: cell surface oligosaccharides composed of N-acetyllactosamine as a repeating disaccharide unit, based on chemical and enzymatic approaches. Substrate specificity and feasibility of a bacterial glycosyltransferase, Neisseria meningitidis beta1,3-N-acetylglucosaminyltransferase (LgtA), were investigated in order to synthesize various key intermediates suited for the construction of mammalian O-glycopeptides and glycosphingolipids containing poly-N-acetyllactosamine structures. Recombinant LgtA exhibited the highest glycosyltransferase activity with strongly basic conditions (pH = 10, glycine-NaOH buffer) and a broad range of optimal temperatures from 20 to 30 degrees C. Interestingly, it was found that LgtA discriminates L-serine and L-threonine and functions both as a core-1 beta1,3-N-acetylglucosaminyltransferase and core-2 beta1,3-N-acetylglucosaminyltransferase toward Fmoc-Ser derivatives, while LgtA showed only core-2 beta1,3-N-acetylglucosaminyltransferase activity in the presence of Fmoc-Thr derivatives. Combined use of LgtA with human beta1,4-galactosyltransferase allowed for controlled sugar extension reactions from synthetic sugar amino acids and gave synthetic lactosaminoglycans, such as a decasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (6), and a dodecasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (9). A partially protected pentasaccharide intermediate, GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Thr-OH (11), was applied for the microwave-assisted solid-phase synthesis of a MUC1-related glycopeptide 19 (MW = 2610.1). The findings suggest that this sugar extension strategy can be employed for the modification of lactosyl ceramide mimetic polymers to afford convenient precursors for the synthesis of various glycosphingolipids.

Nucleoside deoxyribosyltransferase-II (NdRT-II) of Lactobacillus helveticus, which catalyzes the transfer of a glycosyl residue from a donor deoxyribonucleoside to an acceptor base, has a broad specificity for the acceptor bases. Six-substituted purines were found to be substrates as acceptor bases for NdRT-II. Using this property of the enzyme, we established a practical procedure for enzymatic synthesis of 2'-deoxyguanosine (dGuo), consisting of the transglycosylation from thymidine to 6-substituted purine (2-amino-6-chloropurine; ACP) instead of natural guanine and the conversion of 2-amino-6-chloropurine-2'-deoxyriboside (ACPdR) to dGuo with bacterial adenosine deaminase. Through the successive reactions, dGuo was synthesized in high yield.

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