Total synthesis of enantiopure pyrrhoxanthin: alternative methods for the stereoselective preparation of 4-alkylidenebutenolides.
A new stereocontrolled total synthesis of the configurationally labile C37 -norcarotenoid pyrrhoxanthin in enantiopure form has been completed. A highly stereoselective Horner-Wadsworth-Emmons (HWE) condensation of a C17-allylphosphonate and a C20-aldehyde was used as the last conjunctive step. Both a Sonogashira reaction to form the C17-phosphonate and the final HWE condensation proved to be compatible with the sensitive C7-C10 enyne E configuration. Regioselective (5-exo-dig) silver-promoted lactonization reactions of three alternative pent-2-en-4-ynoic acid precursors with increased complexity, including a fully functionalized C20-fragment, were explored for the preparation of the γ-alkylidenebutenolide fragment. This survey extends the existing methodologies for the preparation of oxygen-containing carotenoids (xanthophylls) and streamlines the synthesis of additional members of the C37-norcarotenoid butenolide family of natural products.
Organic Chemistry Department, Universidade de Vigo, Lagoas-Marocosende s/n, 36310 Vigo (Spain). belenvaz@uvigo.es.
Belén
B
Vaz
Leticia
L
Otero
Rosana
R
Álvarez
Ángel R
ÁR
de Lera
D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry; D001688:Biological Products; D002338:Carotenoids / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D001688:Biological Products; C520451:pyrrhoxanthin; D002338:Carotenoids; C004511:butenolide; D015107:4-Butyrolactone
catalysis; marine carotenoids; polyenes; pyrrhoxanthin; total synthesis