Biological properties of D- and L-1-deoxyazasugars

L-Enantiomers of 1-deoxynojirimycin (DNJ), 1-deoxymannojirimycin (manno-DNJ), 1-deoxyallonojirimycin (allo-DNJ), 1-deoxyaltronojirimycin (altro-DNJ), 1-deoxygalactonojirimycin (galacto-DNJ), 1-deoxygulonojirimycin (gulo-DNJ), and 1-deoxyidonojirimycin (ido-DNJ) were prepared according to prior methods for the D-enantiomers. These enantiospecific syntheses established unambiguously the absolute configuration of naturally occurring DNJ, manno-DNJ, allo-DNJ, altro-DNJ, and gulo-DNJ. Although D-DNJ and D-galacto-DNJ are known to be powerful competitive inhibitors of α-glucosidase and α-galactosidase, respectively, with K_i values in the nM range, L-DNJ and L-galacto-DNJ were noncompetitive inhibitors of α-glucosidase and α-galactosidase, respectively, with K_i values in the μM range. However, the azasugar mimicking the structure of the terminal sugar moiety of the natural substrate is not always an inhibitor of the glycosidase responsible for the hydrolysis. D-manno-DNJ is known as a much better inhibitor of α-L-fucosidase than α-mannosidase, while L-allo-DNJ was a better inhibitor than D-manno-DNJ of α-mannosidase. L-galacto-DNJ can be regarded as the 6-hydroxylated derivative of deoxyfuconojirimycin (DFJ), which is a powerful inhibitor of α-L-fucosidase with a K_i value in the nM range. However, this replacement of the methyl group in DFJ by a hydroxymethyl group reduced its affinity by about 50-fold. This suggests that there is a hydrophobic region in or around the active site of α-L-fucosidase. It has been found that inhibitors of human lysosomal glycosidases have therapeutic potential for the corresponding lysosomal storage diseases (Nat. Med. 1999, 5, 112; Proc. Natl. Acad. Sci. USA, 2002, 99, 15428). Inhibition of human lysosomal glycosidases by the 1-deoxyazasugars synthesized was investigated. D-galacto-DNJ is a potent inhibitor of lysosomal α-galactosidase (IC ₅₀ = 90 nM) and is now being evaluated preclinically for its potential use in Fabry disease, while D-DNJ inhibiting α-glucosidase (IC₅₀ = 40 nM) potently does not appear to become a potential therapeutic agent because of additional inhibitory activity toward glycoprotein processing α-glucosidases. On the other hand, although L-allo-DNJ is a moderate inhibitor of α-mannosidase (IC₅₀ = 64 μM), it may become a key compound for the drug design of potential therapeutic agents for α-mannosidosis.