“…Sodium borohydride is commonly employed for these reductive alkylation processes, ,,,,,,,,, although it reduces both the imine and the aldehyde groups, thereby limiting the number of attachments between the enzyme and the activated carbohydrate. Sodium cyanoborohydride, a mild reducing agent that does not reduce aldehyde groups, has been also used. ,− ,,, However, the toxicity associated with the cyanide as well as the inhibitory effect that reactive aldehyde groups cause on the catalytic activity of several enzymes are the main drawbacks of NaBH 3 CN. The latter can be solved by using sequential reduction steps with NaBH 3 CN and NaBH 4 . − Borane–pyridine complex has been also employed as reducing agent for preparing neoglycoenzymes via reductive alkylation with periodate-oxidized carbohydrates …”