An improved synthesis of the oxepinochromone ptaeroxylin is reported, together with the syntheses of the related natural products ptaeroxylinol and eranthin. Ptaeroxylin and ptaeroxylinol were obtained from the chromenone noreugenin by selective reaction of the 7-hydroxyl group, allylation of the 5-hydroxyl, followed by Claisen rearrangement under microwave conditions with concomitant deprotection of the 7-hydroxyl. Alkylation of the 7-hydroxyl with the appropriate allyl bromide provides a precursor for ring-closing metathesis to deliver the oxepinochromone ring system. Eranthin was obtained by a similar strategy involving Claisen rearrangement to transfer an allyl group from the C-7 hydroxyl of noreugenin to C-8 regioselectively.

Derivatives of new ring systems 11H-pyrido[3',2':4,5]pyrrolo[3,2-c]cinnoline and pyrido[3',2':4,5]pyrrolo[1,2-c][1,2,3]benzotriazine have been prepared from the key intermediates 2-(1H-pyrrolo[2,3-b]pyridin-2-yl)anilines in excellent yields (94-99%) and screened by the National Cancer Institute (Bethesda, MD) on about 60 human tumor cell lines derived from nine cancer cell types. The tested compounds exhibited antiproliferative activity against all the human cell lines, showing comparable MG_MID (mean graph midpoint) values in the range of 0.74-1.15 μM. A particular efficacy was observed against the leukemia subpanel (GI50 = 0.73-0.0090 μM). Flow cytometric analysis of the cell cycle demonstrated an increase in the percentage of cells in the G2/M phase. The compounds caused apoptosis of the cells, mitochondrial depolarization, generation of reactive oxygen species, and activation of caspase-3, caspase-8, and caspase-9. Moreover, they acted as topoisomerase I inhibitors.

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The first synthesis of the oxepinochromone ptaeroxylin (also known as desoxykarenin) isolated from the sneezewood tree is described, in which the key steps are a Claisen rearrangement and a ring-closing metathesis to form the seven-membered oxygen heterocyclic ring.