3-Aryl-2,5-Dihydropyrroles via Catalytic Carbonyl-Olefin Metathesis.

Herein, we describe the development of a synthetic strategy towards chiral 3-pyrrolines based on the design principle of iron(III)-catalyzed carbonyl-olefin metathesis. This approach takes advantage of commercially available amino acids as chiral pool reagents and FeCl3 as a Lewis acid catalyst. Our strategy is characterized by its operational simplicity, mild reaction conditions and functional group tolerance. Investigations show that an electron-deficient nitrogen protecting group overcomes limitations arising from competitive binding of the Lewis acid catalyst to unfavorable Lewis basic sites, which ultimately enables catalytic turnover.

Synthesis of resveratrol tetramers via a stereoconvergent radical equilibrium.

Persistent free radicals have become indispensable in the synthesis of organic materials through living radical polymerization. However, examples of their use in the synthesis of small molecules are rare. Here, we report the application of persistent radical and quinone methide intermediates to the synthesis of the resveratrol tetramers nepalensinol B and vateriaphenol C. The spontaneous cleavage and reconstitution of exceptionally weak carbon-carbon bonds has enabled a stereoconvergent oxidative dimerization of racemic materials in a transformation that likely coincides with the biogenesis of these natural products. The efficient synthesis of higher-order oligomers of resveratrol will facilitate the biological studies necessary to elucidate their mechanism(s) of action.

Synthesis, pH-dependent, and plasma stability of meropenem prodrugs for potential use against drug-resistant tuberculosis.

Meropenem, a broad-spectrum parenteral ß-lactam antibiotic, in combination with clavulanate has recently shown efficacy in patients with extensively drug-resistant tuberculosis. As a result of meropenem's short half-life and lack of oral bioavailability, the development of an oral therapy is warranted for TB treatment in underserved countries where chronic parenteral therapy is impractical. To improve the oral absorption of meropenem, several alkyloxycarbonyloxyalkyl ester prodrugs with increased lipophilicity were synthesized and their stability in physiological aqueous solutions and guinea pig as well as human plasma was evaluated. The stability of prodrugs in aqueous solution at pH 6.0 and 7.4 was significantly dependent on the ester promoiety with the major degradation product identified as the parent compound meropenem. However, in simulated gastrointestinal fluid (pH 1.2) the major degradation product identified was ring-opened meropenem with the promoiety still intact, suggesting the gastrointestinal environment may reduce the absorption of meropenem prodrugs in vivo unless administered as an enteric-coated formulation. Additionally, the stability of the most aqueous stable prodrugs in guinea pig or human plasma was short, implying a rapid release of parent meropenem.