Inhibition of the α-l-arabinofuranosidase III of Monilinia fructigena by 1,4-dideoxy-1,4-imino-l-threitol and 1,4-dideoxy-1,4-imino-l-arabinitol

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Abstract
1. 1,4-Dideoxy-1,4-imino-L-threitol was synthesized and the synthesis of 1,4-dideoxy-1,4-imino-L-arabinitol was improved. 2. Both compounds are competitive inhibitors of Monilinia fructigena .alpha.-L-arabino-furanosidase III, the additional hydroxymethyl group in the arabinitol contributing about 17.8 kJ/mol (4.25 kcal/mol) to the Gibbs free energy of binding. 3. The affinities (1/Ki) of both compounds vary with pH in a classical bell-shaped way, the pKa value being that the acid-catalytic group on the enzyme [5,9; Selwood and Sinnott (1988) Biochem. J. 254, 899-901] and the pKb values being those of the free inhibitors, 7.6 and 7.8 respectively. 4. On the basis of these and literature data we suggest that efficient inhibition of glycosidase at its pH by an appropriate iminoalditol will be found when the pKa of the iminoalditol is below that of the acid-catalytic group of the target enzyme.