Cardenolide synthesis studies

BR biosynthesis inhibitors are potentially valuable tools for studying BR biosynthesis (Asami and Yoshida, 1999). Triazoles are known BR biosynthesis inhibitors however, they are not very specific and also suppress the synthesis of gibberellic acid (Rademacher, 2000) or cardenolides (see above). A more specific BR biosynthesis inhibitor, brassinazole, was synthesized by modifying uniconazole (Min et al., 1999). Treatment of Arabidopsis seedlings with brassinazole resulted in a phenotype typical of BR-deficient mutants (Asami... 

More common is use of intramolecular Heck reactions to fashion ckv-decalins. Several examples are found in our current program aimed at the total synthesis of complex cardenolides [14,15]. In a model study for a proposed synthesis of (-t-)-ouabagenin (48), trienyl triflate 45 was converted to pentacycle 47 in good yield (Scheme 6-8) [16]. The stereochemical outcome of this cyclization was rationalized by the preference for an eclipsed orientation of the two reacting bonds, which is readily achieved in a cyclization geometry (46), and led to the cis stereoisomer. This example also highlights the stability of... 

Further studies in the synthesis of 14-deoxy-14a-strophanthidin were reported.220 221 A new synthesis of 15-hydroxy-cardenolides involved the addition of 2-methoxy-4-furyl lithium to A15-17-oxo-compounds as a key step.222 A novel approach to cardenolides from 17-oxo-steroids is outlined223 in Scheme 13. Anhydroxysmalo-... 

Laschat, S., Narjes, F. and Overman, L.E. (1994) Apphcation of intramolecular Heck reactions to the preparation of steroid and terpene intermediates having cis A-B ring fusions. Model studies for the total synthesis of complex cardenolides. Tetrahedron, 50, 347-58. 

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