Studies on total synthesis of cylindrospermopsin: new constructions of uracils from α,β-unsaturated esters

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

In vitro hepatotoxicity of the cyanobacterial alkaloid cylindrospermopsin and related synthetic analogues

Cylindrospermopsin (CY), a sulfate ester of a tricyclic guanidine substituted with a hydroxymethyluracil, is a cyanobacterial toxin of increasing environmental import as it frequently occurs in drinking water reservoirs. As a toxin, CY mainly targets the liver but also involves other organs. In hepatocytes CY inhibits the synthesis of protein and of glutathione, leading to cell death. The total chemical synthesis of CY has recently been reported (Xie et al., 2000, J. Am. Chem. Soc. 22, 5017-5024). The synthesis has provided analogues of CY to study aspects of the relationship between chemical structure and activity that contribute to toxicity. Protein synthesis inhibition was measured in vitro using a rabbit reticulocyte system. Primary cultures of rat hepatocytes were used to determine the biological activity of CY and analogues in intact cells. Protein synthesis and cell glutathione levels were measured. We could distinguish between CY transport and biological activity by comparing the results in vitro to those in intact cells. The role of the sulfate group in CY toxicity was examined by comparing biological effects of CY with that of CY-DIOL (synthetic CY lacking the sulfate group). The sulfate group was found not to play a role in CY activity or in its uptake into cells, since there was no significant difference in biological activity in vitro or in cells between natural CY and CY-DIOL. The orientation of the hydroxyl group at C7 also had no impact on biological activity or transport of CY, since the C7 epimer of CY (EPI-CY) and the corresponding diol (EPI-DIOL) had activity similar to RAC-CY in vitro and in intact cells. AB-MODEL, the analogue lacking an intact C ring, and the methyl and hydroxyl groups of ring A could inhibit protein synthesis (but at concentrations 500-1000-fold higher than natural CY). Other structurally simpler synthetic analogues lacked biological activity.

N-Benzylhydroxylamine addition to beta-aryl enoates. Enantioselective synthesis of beta-aryl-beta-amino acid precursors

Chiral Lewis acid catalyzed N-benzylhydroxylamine addition to pyrrolidinone-derived enoates afforded beta-aryl-beta-amino acid derivatives in high enantiomeric purity with moderate to very good chemical efficiency.