An Amination-Cyclization Cascade Reaction for Iminosugar Synthesis Using Minimal Protecting Groups

Synthesis and glycosidase inhibition of 3,4,5-trihydroxypiperidines using a one-pot amination-cyclisation cascade reaction

Trihydroxypiperidines are a therapeutically valuable class of iminosugar. We applied a one-pot amination-cyclisation cascade reaction to synthesise 3,4,5-trihydroxypiperidine stereoisomers in three steps from commercially available pentoses and in excellent overall yields. Using our methodology, the yields of the syntheses of meso-1, meso-2 and 3L are the highest reported to date. The synthetic methodology was readily extended to the three-step synthesis of N-alkyl derivatives by replacing the ammonia nitrogen source with a primary amine. The trihydroxypiperidines and N-alkyl analogues were screened for enzyme inhibitory activity using Fabrazyme (Fabry disease), GCase (Gaucher's disease), Agrobacterium sp. β-glucosidase, and Escherichia coli β-galactosidase. N-Phenylethyl 3,4,5-trihydroxypiperidine (N-phenylethyl-1-(3R,4R,5S)-piperidine-3,4,5-triol) showed good inhibitory activity of Fabrazyme (Ki = 46 μM). This activity was abolished when the N-phenylethyl group was removed or replaced with a non-aromatic alkyl chain.

Synthesis of 1-Deoxymannojirimycin from d-Fructose using the Mitsunobu Reaction

Three different Mitsunobu reactions have been investigated for the synthesis of 1-deoxymannojirimycin (1-DMJ) from d-fructose. The highest yielding and most practical synthesis can be undertaken on a 10 g scale with minimal chromatography. In the key step, N,O-di-Boc-hydroxylamine reacts with methyl 1,3-isopropylidene-α-d-fructofuranose under Mitsunobu conditions to give 14. Acidic hydrolysis affords nitrone 15, which reduces quantitatively via catalytic hydrogenolysis to afford 1-DMJ (4) in 55% overall yield from d-fructose (cf. 37% for azide route and 29% for nosyl route).