On the effect of the aglycon structure of three aryl beta-D-galactosides on the yield and the regioselectivity of the transglycolytic synthesis of N-acetyllactosamine

We examined the effect as donors of three aryl beta-D-galactosides (i.e. p- nitrophenyl beta-D-galactopyranoside, o-nitrophenyl beta-D-galactopyranosid e and phenyl beta-D-galactopyranoside) on the regioselectivity and the yiel d of the synthesis of N-acetyllactosamine obtained from the transglycosylat ion reaction catalyzed by a crude preparation of beta-D-galactosidase from Bacillus circulans at 25 degrees C, 37 degrees C and 55 degrees C, respecti vely. Using p-nitrophenyl beta-D-galactopyranoside the reaction results wer e fully regiospecific at all the temperatures considered: the maximum molar yield (74%) was obtained at an incubation temperature of 55 degrees C. Usi ng o-nitrophenyl beta-D-galactopyranoside as the donor the reaction was sti ll highly regioselective and the maximum molar yield (50%) was achieved at an incubation temperature also of 55 degrees C. Using phenyl beta-D-galacto pyranoside transglycolytic products appear only at an incubation temperatur e of 55 degrees C but at very low molar yield (about 14%) and lower regiose lectivity.