Enzymatic synthesis of a new inhibitor of alpha-amylases: acarviosinyl-isomaltosyl-spiro-thiohydantoin. 
Synthesis of acarviosinyl-isomaltosyl-spiro-thiohydantoin in yields up to 20%, has been achieved by Bacillus stearothermophilus maltogenic amylase (BSMA).  BSMA is capable of transferring the acarviosine-glucose residue from an acarbose donor onto glucopyranosylidene-spiro-thiohydantoin.  Reactions were followed using HPLC and MALDI-TOF MS.  1H and 13C NMR studies revealed that the enzyme reserved its stereoselectivity.  Glycosylation took place mainly at C-6 resulting in alpha-acarviosinyl-(1-->4)-alpha-D-glucopyranosyl-(1-->6)-D-glucopyranosylidene-spiro-thiohydantoin.  This compound was found to be a much more efficient salivary amylase inhibitor than glucopyranosylidene-spiro-thiohydantoin with kinetic constants of K(EI)=0.19 microM and K(ESI)=0.24 microM.