Isolation and unambiguous synthesis of cryptolepinone: An oxidation artifact of cryptolepine

Cryptolepinone (3) was isolated as an artifact of extraction from Cryptolepis sanguinolenta. Previously, this compound had been identified as the natural products hydroxycryptolepine (2) and 3. Synthesis via an unambiguous pathway has confirmed the structure of cryptolepinone. Spectroscopic studies in various solvents have shown that the natural product artifact or its synthetic equivalent can exist in the keto (cryptolepinone) or enol (hydroxycryptolepine) form.