Enzymatic Synthesis of Aliphatic β-Lactosides as Mimic Units of Glycosphingolipids by Use of Trichoderma reesei Cellulase

Aliphatic β-lactosides were directly synthesized by β-lactosyl transfer reaction from p-nitrophenyl β-lactoside (Lacβ-pNP) to various 1-alkanols (n = 2–12), utilizing commercially available cellulase preparation of Trichoderma reesei C1. With ethanol acceptor, the enzyme induced ethyl β-lactoside (1) in 18% yield based on the donor added in aqueous buffer system. When 1-octanol and dodecanol were acceptors, octyl β-lactoside (2) and dodecyl β-lactoside (3) were also obtained as transfer products, respectively. In both cases, the addition of sodium cholate as detergent to the reaction system ensured a sufficient solubility of these acceptors and resulted in a remarkable increase of the desired compounds(5–13% yields based on the donor added). Furthermore, the enzyme catalyzed the N-acetyllactosaminyl transfer reaction from p-nitrophenyl β-N-acetyllactosaminide(LacNAcβ-pNP) not only to 1-alkanol, but also to the OH-4 position of Man and Glc to produce the trisaccharides, Galβ1-4GlcNAcβ1-4Man (4) and Galβ1-4GlcNAcβ1-4Glc (5), respectively. The enzyme activities transferring lactosyl and N-acetyllactosaminyl groups were not separated by chromatographies using DEAE–Sepharose Fast Flow and Sephadex 75 pg columns, indicating that the two reactions were catalyzed by a single enzyme. It was specified that a single enzyme works both transglycosylations, based on the substrate competition assay on hydrolysis.