Synthesis and Evaluation of Eight- and Four-Membered Iminosugar Analogues as Inhibitors of Testicular Ceramide-Specific Glucosyltransferase, Testicular β-Glucosidase 2, and Other Glycosidases

Eight- and four-membered analogues of N-butyldeoxynojirimycin (NB-DNJ), a reversible male contraceptive
in mice, were prepared and tested. A chiral pool approach was used
for the synthesis of the target compounds. Key steps for the synthesis
of the eight-membered analogues involve ring-closing metathesis and
Sharpless asymmetric dihydroxylation and for the four-membered analogues
Sharpless epoxidation, epoxide ring-opening (azide), and Mitsunobu
reaction to form the four-membered ring. (3S,4R,5S,6R,7R)-1-Nonylazocane-3,4,5,6,7-pentaol (6) was moderately
active against rat-derived ceramide-specific glucosyltransferase,
and four of the other eight-membered analogues were weakly active
against rat-derived β-glucosidase 2. Among the four-membered
analogues, ((2R,3S,4S)-3-hydroxy-1-nonylazetidine-2,4-diyl)­dimethanol
(25) displayed selective inhibitory activity against
mouse-derived ceramide-specific glucosyltransferase and was about
half as potent as NB-DNJ against the rat-derived enzyme. ((2S,4S)-3-Hydroxy-1-nonylazetidine-2,4-diyl)­dimethanol
(27) was found to be a selective inhibitor of β-glucosidase
2, with potency similar to NB-DNJ. Additional glycosidase assays were
performed to identify potential other therapeutic applications. The
eight-membered iminosugars exhibited specificity for almond-derived
β-glucosidase, and the 1-nonylazetidine 25 inhibited
α-glucosidase (Saccharomyces cerevisiae) with
an IC50 of 600 nM and β-glucosidase (almond) with
an IC50 of 20 μM. Only N-nonyl derivatives
were active, emphasizing the importance of a long lipophilic side
chain for inhibitory activity of the analogues studied.