Polyhydroxylated pyrrolidines: synthesis from d-fructose of new tri-orthogonally protected 2,5-dideoxy-2,5-iminohexitols

Introducing Lipophilicity to (Polyhydroxyalkyl)thiazolidine Carboxylic Acids Via Acylation

The therapeutic efficacy of bioactive compounds is related to their bioavailability. In turn, the bioavailability depends on the equilibrium between the hydrophilicity and the lipophilicity. 2(R,S)-(Polyhydroxyalkyl)thiazolidine-4(R) carboxylic acids (TCAs), obtained from the condensation of l-cysteine and an aldose, have been recognized as nontoxic precursors of glutathione with important preventive and therapeutic effects. The bioavailability of these compounds can be improved by enhancing their lipophilicity. This can be achieved by the introduction of some acyl groups derived from fatty acids via esterification of the aldose hydroxyl groups. With this purpose four new compounds were synthesized through a selective palmitoyl acylation of d-(-)-ribose and d-(+)-glucose and subsequent condensation with l-cysteine. In addition, the log P of the new compounds was calculated as a measure of the lipophilicity, and in vitro 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) tests were performed as a measure of the antioxidant capability.

Iminosugars as glycosyltransferase inhibitors

Iminosugars are naturally occurring carbohydrate analogues known since 1967. These natural compounds and hundreds of their synthetic derivatives prepared over five decades have been mainly exploited to inhibit the glycosidases, the enzymes catalysing the glycosidic bond cleavage, in order to find new drugs for the treatment of type 2 diabetes and other diseases. However, iminosugars are also inhibitors of glycosyltransferases, the enzymes responsible for the synthesis of oligosaccharides and glycoconjugates. The selective inhibition of specific glycosyltransferases involved in cancer or bacterial infections could lead to innovative therapeutic agents. The synthesis and biological properties of all the iminosugars assayed to date as glycosyltransferase inhibitors are reviewed in the present article.

Synthesis of a poly-hydroxypyrolidine-based inhibitor of Mycobacterium tuberculosis GlgE

Long treatment times, poor drug compliance, and natural selection during treatment of Mycobacterium tuberculosis (Mtb) have given rise to extensively drug-resistant tuberculosis (XDR-TB). As a result, there is a need to identify new antituberculosis drug targets. Mtb GlgE is a maltosyl transferase involved in α-glucan biosynthesis. Mutation of GlgE in Mtb increases the concentration of maltose-1-phosphate (M1P), one substrate for GlgE, causing rapid cell death. We have designed 2,5-dideoxy-3-O-α-d-glucopyranosyl-2,5-imino-d-mannitol (9) to act as an inhibitor of GlgE. Compound 9 was synthesized using a convergent synthesis by coupling thioglycosyl donor 14 and 5-azido-3-O-benzyl-5-deoxy-1,2-O-isopropylidene-β-d-fructopyranose (23) to form disaccharide 24. A reduction and intramolecular reductive amination transformed the intermediate disaccharide 24 to the desired pyrolidine 9. Compound 9 inhibited both Mtb GlgE and a variant of Streptomyces coelicolor (Sco) GlgEI with K_i = 237 ± 27 μM and K_i = 102 ± 7.52 μM, respectively. The results confirm that a Sco GlgE-V279S variant can be used as a model for Mtb GlgE. In conclusion, we designed a lead transition state inhibitor of GlgE, which will be instrumental in further elucidation of the enzymatic mechanism of Mtb GlgE.

Structure-guided minimalist redesign of the L-fuculose-1-phosphate aldolase active site: expedient synthesis of novel polyhydroxylated pyrrolizidines and their inhibitory properties against glycosidases and intestinal disaccharidases

A minimalist active site redesign of the L-fuculose-1-phosphate aldolase from E. coli FucA was envisaged, to extend its tolerance towards bulky and conformationally restricted N-Cbz-amino aldehyde acceptor substrates (Cbz=benzyloxycarbonyl). Various mutants at the active site of the FucA wild type were obtained and screened with seven sterically demanding N-Cbz-amino aldehydes including N-Cbz-prolinal derivatives. FucA F131A showed an aldol activity of 62 μmol h(-1) mg(-1) with (R)-N-Cbz-prolinal, whereas no detectable activity was observed with the FucA wild type. For the other substrates, the F131A mutant gave aldol activities from 4 to about 25 times higher than those observed with the FucA wild type. With regard to the stereochemistry of the reactions, the (R)-amino aldehydes gave exclusively the anti configured aldol adducts whereas their S counterparts gave variable ratios of anti/syn diastereoisomers. Interestingly, the F131A mutant was highly stereoselective both with (R)- and with (S)-N-Cbz-prolinal, exclusively producing the anti and syn aldol adducts, respectively. Molecular models suggest that this improved activity towards bulky and more rigid substrates, such as N-Cbz-prolinal, could arise from a better fit of the substrate into the hydrophobic pocket created by the F131A mutation, due to an additional π-cation interaction with the residue K205' and to efficient contact between the substrate and the mechanistically important Y113' and Y209' residues. An expedient synthesis of novel polyhydroxylated pyrrolizidines related to the hyacinthacine and alexine types was accomplished through aldol additions of dihydroxyacetone phosphate (DHAP) to hydroxyprolinal derivatives with the hyperactive FucA F131A as catalyst. The iminocyclitols obtained were fully characterised and found to be moderate to weak inhibitors (relative to 1,4-dideoxy-1,4-imino-L-arabinitol (LAB) and 1,4-dideoxy-1,4-imino-D-arabinitol (DAB)) against glycosidases and rat intestinal saccharidases.