Oxytrofalcatin Puzzle: Total Synthesis and Structural Revision of Oxytrofalcatins B and C

The previously reported structures of oxytrofalcatins B and C possess a benzoyl indole core. However, following synthesis and NMR comparison of both the proposed structure and the synthesized oxazole, we have revised the structure of oxytrofalcatins B and C as oxazoles. The synthetic route developed herein can further our understanding of the biosynthetic pathways that govern the production of natural 2,5-diaryloxazoles.

Trypanocidal Activity of 2,5-Diphenyloxazoles Isolated from the Roots of Oxytropis lanata

Eleven 2,5-diphenyloxazole derivatives (1-11), together with six known isoflavonoid derivatives, were isolated from the roots of Oxytropis lanata. The 2,5-diphenyloxazole (1) obtained proved to be identical to a standard sample used as a scintillator and liquid laser dye. The other oxazole derivatives isolated were found to have one to four hydroxy and/or O-methyl groups in their phenyl rings. Seven of the oxazole derivatives obtained are new (3-9). The inhibitory activity of the isolated compounds was evaluated against Trypanosoma congolense, the causative agent of African trypanosomosis in animals. Oxazoles with di- and trihydroxy groups showed trypanocidal activity, and 2-(2',3'-dihydroxyphenyl)-5-(2″-hydroxyphenyl)oxazole (4) exhibited the most potent inhibitory activity (IC₅₀ 1.0 μM).

Highly enantioselective construction of tertiary thioethers and alcohols via phosphine-catalyzed asymmetric γ-addition reactions of 5H-thiazol-4-ones and 5H-oxazol-4-ones: scope and mechanistic understandings

Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroatom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides facile access to enantioenriched tertiary thioethers/alcohols. The mechanism of the γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the "C[double bond, length as m-dash]O" unit of the donor molecules were shown to be crucial in asymmetric induction.

The metabolism of 2,5-diphenyloxazole (PPO) in human lymphocytes and rat liver microsomes

The oxidative metabolism of 2,5-diphenyloxazole (PPO) is associated with 3-methylcholanthrene inducible cytochrome P-450. The major metabolite formed has m/z of 237, corresponding to hydroxylated PPO. All the possible hydroxylated metabolites of PPO were synthesized and characterized, enabling the assignment of a structure for the major metabolite and two minor metabolites. The metabolites are easily extracted and their fluorescence is quantifiable in alkaline medium with a sample fluorescence to blank fluorescence ratio of 400:1. A sensitive HPLC assay of PPO metabolism was also developed. PPO metabolism is readily catalyzed by 3-methylcholanthrene-induced rat liver microsomes and strongly inhibited by alpha-naphthoflavone, but poorly inhibited by metyrapone or SKF 525A, indicating the involvement of cytochrome P-448 or P1-450 in the metabolism of PPO. With human lymphocytes the method has proven to be a good indicator of "aryl hydrocarbon hydroxylase" (AHH) activity, correlating well with AHH assays using benzo(alpha)pyrene (BP) as a substrate. Both the induced BP and PPO metabolism by human lymphocytes is inhibited by alpha-naphthoflavone, but not by metyrapone.