The ineffectiveness of analogs of D-galactal as competitive inhibitors of, and substrates for, beta-D-galactosidase from Escherichia coli.

2,6-Anhydro-3-deoxy-aldehydo-D-lyxo-hept-2-enose (7) and 2,6-anhydro-3-deoxy-D-lyxo-hept-2-enitol (8) were synthesized as half-chair analogs of D-galactal (1). As 1 is a strong inhibitor of, as well as a substrate for, beta-D-galactosidase from Escherichia coli, the same properties were expected for 7 and 8; however, both were ineffective. This result, together with those of other authors, allows speculative conclusions on the tight binding of 1 to the enzyme only, when water or an alcohol is bound as a co-substrate.