Natural hatching stimuli glycinoeclepins A(1), B(2), and C(3), isolated from dried kidney bean roots, have been confirmed synthetically to have a potent biological activity for the second stage of soybean cyst nematode (Heterodera glycines). Characteristic structures of glycinoeclepins having a common methylene moiety at C19 and various side chains suggest that a cycloartane-type triterpene would be one of the presumable biosynthetic precursors. Accordingly, we chose cycloastragalol(8), isolated from Chinese drug Tragacantha, as a starting material for the biogenetic-type synthesis of glycinoeclepin A analogues. As a model experiment, we could construct the A-ring fragment (7-oxabicyclo[2.2.1]heptane system) of the title target in a quantitative yield starting with a cycloartane(5). As a next stage, cycloastragalol(8) was converted into diene(24) involving the functionalization for the B-ring cleavage as well as formation of the A-ring moiety. Compound 24 was then transformed into the desired product(29), which was formed by a hydride shift from C17 to C16 followed by a methyl migration from C13 to C17 in a backbone rearranged manner. The second methyl migration to C13 from C14 is now under investigation. The structure and biological activity-relationships of the synthetic intermediates would be also discussed briefly.
