Synthesis of (−)-callicarpenal, a potent arthropod repellent

Abstract

Callicarpenal (1), a natural terpenoid isolated from American beautyberry (Callicarpa americana), has shown significant repellent activities against mosquitoes, ticks and imported fire ants. Here we report our efficient synthetic approach to this natural product, and preliminary results of the mosquito biting-deterrent effects of callicarpenal as well as its synthetic precursors and related C 8 -epimers. The synthetic strategy allows rapid access to various epimers and analogues of the natural product that can be used to explore its structure-activity relationship and optimize its biological properties.

Conjuring a Supernatural Product – DelMarine

“…This intermediate was unstable due to the high electrophilicity of the prenyl bromide moiety in combination with the nucleophilicity of the purine ring, but it could be stored briefly as a dilute solution at low temperature. The (methyl)-Wieland-Miescher ketal ketone 30 (99% ee) 37 was then subjected to dissolving metal reduction in the presence of bis(2-methoxyethyl)amine, 38 and trapped at low temperature with bromide 29 to yield the reductively alkylated ketone 31 as a single stereoisomer. This reductive alkylation reaction was particularly taxing because of the instability of bromide 29.…”

Unexpected Racemization in the Course of the Acetalization of (+)-(S)-5-Methyl-Wieland–Miescher Ketone with 1,2-Ethanediol and TsOH under Classical Experimental Conditions

“…In the course of our work on bioactive natural products and bioactive materials [117][118][119][120][121][122][123][124], it occurred to us to observe the partial racemization of (+)-5 during the acetalization of (+)-1 with 1,2-ethanediol and TsOH in the presence of a Dean-Stark apparatus. According to our best knowledge, obtaining partially racemized (+)-5 or (−)-5 when the acetalization reaction is carried out by this procedure on (+)-1 or (-)-1 [33,35,39,40,44,48,49,72,77,81,84,[87][88][89][90][91]116], respectively, has not been previously reported in the literature, which was the reason behind investigating this reaction.…”

Total Synthesis of Anti‐Cancer Meroterpenoids Dysideanone B and Dysiherbol A and Structural Reassignment of Dysiherbol A

“…With the retrosynthetic analysis in mind, we started the adventure from the synthesis of common precursors for the cyclization reactions, as shown in Scheme 1. To this end, the more reactive unconjugated ketone functionality of Wieland-Miescher ketone derivative 17, which could be efficiently prepared from commercially available material in two steps in either racemic or enantiomeric form, [18] was chemoselectively protected as a glycol acetal to give enone 15 in 94 % yield. The combination of bicyclic enone 15 with the bulky benzyl bromide 16 proved challenging with O-or C7-alkylation byproducts observed at different reaction temperatures.…”