[Preparation and structural elucidation of insularine-N-oxides]

Oxidation of insularine (I) with m-chloroperbenzoic acid yielded four insularine-N-oxides. Two of them are identical in every respect with our insularine-2 beta-N-oxide (II) and insularine-2' beta-N-oxide (III), two rare examples of naturally occurring head-to-tail bisbenzylisoquinoline N-oxides newly isolated from Cyclea sutchuenensis, which confirmed the structures of the two novel natural N-oxides. The other two are new compounds and their structures have been established as insularine-2' alpha-N-oxide (IV) and insularine-2 beta,2' beta-N, N-dioxide (V), on the basis of spectral data (UV, IR, 1HNMR, NOEDS AND MS) analysis.