Naturally occurring eccentric cleavage products of provitamin A β-carotene function as antagonists of retinoic acid receptors - PubMed (original) (raw)

Chemical synthesis of all possible β-apocarotenoids. Reagents and conditions used in the synthesis of the various compounds are shown in lowercase roman numerals, and yields are shown in parentheses. i, 5

n

KOH/EtOH (± benzene); room temperature, 12 h (99%, β-ionone; 96%, β-apo-12′-carotenoic acid; 92%, β-apo-10′-carotenoic acid; 94%, β-apo-14′-carotenoic acid). ii, LiAIH4, tetrahydrofuran, room temperature, 45 min (for compound 2, 9); DIBAL-H, CH2Cl2, room temperature, 30 min (for compound 6). iii, MnO2, Celite, CH2Cl2, room temperature, 4 h (73%, β-ionylideneacetaldehyde; 36%, β-apo-10′-carotenal; 6%, β-apo-14′-carotenal). iv, (triphenylphosphoranylidene)-2-propanone, toluene, reflux, 12 h (61%). v, NaH, dialdehyde shown, CH2Cl2, 0 °C to room temperature, 48 h (59%). vi, KCN, CH3COOH, MnO2, MeOH, room temperature, 90 h (21%, 4; 2%; 10). vii, NaH, triethylphosphonoacetate, THF, 0 °C to room temperature, 48 h (83%, 5; 94%, 1; 74%, 8). viii, O2, CH2Cl2, 48 h (quantitative).