1068012-41-8

The synthesis, conformational study and inhibitory properties of diverse indolizidine and quinolizidine iminocyclitols are described. The compounds were chemo-enzymatically synthesized by two-step aldol addition and reductive amination reactions. The aldol addition of dihydroxyacetone phosphate (DHAP) to N-Cbz-piperidine carbaldehyde derivatives catalyzed by l-rhamnulose 1-phosphate aldolase from Escherichia coli provides the key intermediates. The stereochemical outcome of both aldol addition and reductive amination depended upon the structure of the starting material and intermediates. The combination of both reactions furnished five indolizidine and six quinolizidine type iminocyclitols. A structural analysis by NMR and in silico density functional theory (DFT) calculations allowed us to determine the population of stereoisomers with the trans or cis ring fusion, as a consequence of the inversion of configuration of the bridgehead nitrogen. The trans fusion was by far the most stable, but for certain stereochemical configurations of the 3-hydroxymethyl and hydroxyl substituents both trans and cis fusion stereoisomers coexisted in different proportions. Some of the polyhydroxylated indolizidines and quinolizidines were shown to be moderate to good inhibitors against α-l-rhamnosidase from Penicillium decumbens. Indolizidines were found to be moderate inhibitors of the rat intestinal sucrase and of the exoglucosidase amyloglucosidase from Aspergillus niger. In spite of their activity against α-l-rhamnosidase, all the compounds were ineffective to inhibit the growth of the Mycobacterium tuberculosis, the causative agent of tuberculosis. The Royal Society of Chemistry 2012.

The diastereoselective auxiliary-based intramolecular Michael-type additions to alkylidene bissulfoxides derived from dithiane and dithiolane were investigated. Utilization of substrates bearing N- and O-nucleophilic functions led to the formation of the

The first enantioselective total syntheses of the phenanthroquinolizidine alkaloid (-)-cryptopleurine (1) and its seco base (-)-julandine [(R)-3] are described. The synthesis of (R)-3 allowed the 9aS configuration to be assigned to natural dextrorotatory julandine as shown by structure (S)-3. Both synthetic approaches are based on the high degree of 1,3-asymmetric induction achieved using an N-acylhydrazonium salt, which belongs to a new structural class of activated azomethines. Upon exposure of methoxylactam 9, with a chiral 2-substituted pyrrolidine auxiliary, to BF3·Et2O and a silyl enol ether the in situ generated N-acylhydrazonium intermediate 10 underwent asymmetric nucleophilic addition to give the (6R)-keto lactams 13 and 14 with complete diastereoselectivity. On the other hand, nucleophilic addition to the N-acylhydrazonium ion 25, with an acyclic chiral auxiliary, showed poor diastereoselectivity. From these results, the high degree of diastereoselection observed for the N-acylhydrazonium ion 10 can be rationalized in terms of the pyramidal stability of the trivalent nitrogen in the chiral pyrrolidine auxiliary. Removal of the chiral auxiliary from 13 and 14 was achieved by reductive N-N bond cleavage using BH3·THF, affording (2S)-piperidine derivatives 15 and 31, respectively, which were transformed into quinolizidinones 30 and 35, respectively, via intramolecular aldol condensation. Reduction of 30 with alane provided (-)julandine [(R)-3]. In addition, 35 was converted to (-)-cryptopleurine (1) in two steps, by radical cyclization with Bu3SnH and AIBN, followed by LiAlH4 reduction.

Simple routes to (1R,2R,8aR)- and (1S,2S,8aS)-lentiginosine have been described, based on Sharpless asymmetric dihydroxylation, starting from (R)- and (S)-pipecolinic acids.