Twenty-eight natural and unnatural lamellarins with either a saturated or an unsaturated D-ring were synthesized according to our developed synthetic route. The key step involved the Michael addition/ring closure (Mi-RC) of the benzyldihydroisoquinoline and alpha-nitrocinnamate derivatives, which provided the 2-carboethoxypyrrole intermediates in moderate to good yields (up to 78% yield). Subsequent hydrogenolysis/lactonization furnished lamellarins with a saturated D-ring in excellent yields (up to 93% yield). DDQ oxidation of the saturated lamellarin acetates led directly to the corresponding unsaturated analogues in 54-95% yield. In addition, only two steps in our developed strategy require column chromatography.

Solid-supported acids have been investigated for aromatic debenzylation reactions. Stoichiometric amounts of solid-supported acids in refluxing toluene with or without 4 equiv of methanol effectively provided the desired aromatic debenzylation products of various systems in moderate to excellent yields (up to 98%).

Alkaloids U 0600Total Synthesis of Natural and Unnatural Lamellarins with Saturated and Unsaturated D-Rings. -A wide range of title compounds such as (I) and (II) is prepared in order to test their biological activity. -(PLOYPRADITH*, P.; PETCHMANEE, T.; SAHAKITPICHAN, P.; LITVINAS, N. D.; RUCHIRAWAT, S.; J. Org. Chem. 71 (2006) 25, 9440-9448; Lab. Med. Chem., Chulabhorn Res. Inst., Bangkok 10210, Thailand; Eng.) -Jannicke 17-190