A Comparison of Glucose‐ and Glucosamine‐Related Inhibitors: Probing the Interaction of the 2‐Hydroxy Group with Retaining β‐Glucosidases

The inhibition of the β‐glucosidases from sweet almonds and Caldocellum saccharolyticum at varying pH values by the glucosamine‐related inhibitors 1 – 7 has been compared to the inhibition by the known glucose analogues 8 – 14 . The amino derivatives 3 , 4 , 6 , and 7 were prepared in one step from the known 15 – 18 (Scheme 1), and the amino‐1,2,3‐triazole 5 by a variant of the synthesis leading to the glucose analogue 12 (Scheme 2). The key step for the preparation of the aminoimidazole 1 and of the amino‐1,2,4‐triazole 2 is the regioselective cleavage of the benzyloxy group at C(2) of the gluconolactam 35 and the mannonolactam 57 , respectively, by BCl₃ and Bu₄NBr (Schemes 3 and 4, resp.). The pH optimum for the inhibition by the amines is lower than their pK_HA values, evidencing that they are bound as ammonium salts and that H‐bonding between C(2)?NH and the cat. base B^? contributes more strongly to binding than any possible H‐bond to the NH₂?C(2) group. The influence of the ammonium group on the inhibitory strength correlates with the basicity of the `glycosidic heteroatom'. The strongest increase of the inhibitory strength is observed for the amines lacking a `glycosidic heteroatom' (ΔΔG(OH→NH)=?1.5 to ?2.9 kcal/mol). The increase is less pronounced for the amino derivatives 3 – 4 , which possess a weakly basic `glycosidic heteroatom' (ΔΔG(OH→NH)=?0.6 to ?1.1 kcal/mol); the amino compounds 1 and 2 , which possess a strongly basic `glycosidic heteroatom', are weaker inhibitors than the corresponding hydroxy compounds, as expressed by ΔΔG(OH→NH) between +4.3 and +4.7 kcal/mol for the amino‐imidazole 1 , and between +2.3 and 2.8 kcal/mol for the amino‐1,2,4‐triazole 2 , denoting the dominant detrimental influence of a C(2)?NH group on the H‐bond acceptor properties of a sufficiently basic `glycosidic heteroatom'.