Synthesis of the Oxepinochromone Natural Products Ptaeroxylin (Desoxykarenin), Ptaeroxylinol, and Eranthin

Abstract

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.

Chromone and Flavonoid Alkaloids: Occurrence and Bioactivity

“…This plant has shown antineoplastic activity [12]. Cheliensisine belongs to the oxepinochromone family of natural products, for which syntheses are being developed due to their unusual structures and potential for drug development (for example, see [13]).…”

Toward a Synthesis of Hirsutellone B by the Concept of Double Cyclization

“…After titration, a solution of 57 was added to known allylic bromide 58 45 to form the coupled product 59 . Upon workup, the crude product was treated with lithium hydroxide to chemoselectively cleave the phenolic TBS group, giving the desired phenol 60 in 77% yield over the three steps.…”

“…To an oven-dried flask under argon equipped with a magnetic stirring bar was added a solution of allylic bromide 58 45 (2.39 g, 6.13 mmol, 1.00 eq.) in 50 mL of THF.…”

Tandem Claisen Rearrangement/6‐endo Cyclization Approach to Allylated and Pren­ylated Chromones

“…The usefulness of the method is illustrated by the first synthesis of the fungal metabolite pestaloficiol J. In addition, several chromones synthesized in the course of this study have substitution and oxygenation patterns that are present in bioactive plant metabolites, for example, 21r (eranthin [69] ), 21s (peucenin [70] ), 21u (6-prenylapigenin [71] ) and 21w (licoflavone A [72] ). Investigations into the application of microwave-promoted tandem sigmatropic rearrangement/cyclization cascades for target molecule synthesis are currently underway in our laboratory.…”