Preparation, biochemical characterization and biological properties of radiolabelled N-alkylated deoxynojirimycins

We have reductively alkylated deoxynojirimycin imino sugars using sodium cyanoborohydride to provide an efficient means of generating a series of N-alkylated compounds containing 4–18 carbon side chains. The yields were greater than 90% using a variety of aldehydes of different chain lengths, and after purification were >95% pure using ¹H-NMR. Radiolabelled compounds were prepared using sodium cyanoborotriti-ide to selectively label the first carbon atom in the alkyl chain and used in protein-binding and cell- and tissue-uptake experiments. Protein binding was chain-length-dependent with compounds of intermediate chain length (C₉—C₁₂), demonstrating an equal distribution between the aqueous and protein-bound phase. The extent of cell uptake also increased proportionally with increased chain length in a time-dependent manner. When administered to mice, the longer alkyl-chain compounds showed reduced absorption from the intestine and a marked deposition of compound in the liver and brain, suggesting that the more hydrophobic compounds were poorly cleared by the major tissues. In tissue-culture cells compounds with 8 or fewer carbon atoms were non-toxic and had CC₅₀ (the concentration at which the number of cells or cell proliferation is reduced by 50%) values greater than 1mM. Compounds with chain lengths above C₈ showed a chain-length-dependent increase in cytotoxicity. N-alkylated deoxynojirimycins (C₄—C₁₈) were evaluated for their inhibitory effects on ceramide-specific glucosyltransferase and glycoprotein-processing α-glucosidase. Increasing the alkyl chain length had little effect on α-glucosidase activity, but inhibition of ceramide-specific glucosyltransferase increased 10-fold when C₄ and C₉—C₁₈ compounds were compared. Overall these data provide further definition of the molecular features of alkylated imino sugars that influence tissue selectivity and efficacy for cellular enzyme inhibition.