Gastroprotective substance

The first stereoselective total synthesis of AI-77B, a gastroprotective substance, was accomplished by Y. Hamada and co-workers. In the final stages of the synthetic effort, the intramolecular Pinner reaction was utilized to convert the cyano group into the corresponding carboxylic acid. The nitrile substrate was dissolved in 5% HCI in methanol, and excess trimethyl orthoformate was added at 5 °C and the reaction mixture was stirred at this temperature for almost two days. Next, the cyclic imino ether hydrochloride salt was treated with water at room temperature followed by basic hydrolysis. Finally, the pH was adjusted with HCI to obtain the natural product. 

Hamada, Y., Hara, O., Kawai, A., Kohno, Y., Shioiri, T. New methods and reagents in organic synthesis. 97. Efficient total synthesis of Al-77-B, a gastroprotective substance from Bacillus pumilus AI-77. Tetrahedron 99, 47, 8635-8652. 

The pyrrolidine 235, a (25,35)-dihydroxy-(45)-amino acid moiety of the gastroprotective substance AI-77B, was prepared from the known alkene 234 in several steps. The same starting alkene also provided a lactam analogue of 235, namely 236, also a component of A1-77B (Scheme 17). ... 

Although numerous flavonic substances present gastroprotective properties, the mechanisms involved in mucosal defense, are not sufficiently explained and, naturally, they are not the same for each flavonoid. 

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