Apocarotenals of Phenolic Carotenoids for Superior Antioxidant Activities†

[Image: see text] A series of para-phenolic carotenes 1 with ortho- and meta-substitutions were respectively prepared utilizing the benzenesulfonyl protection method, which demonstrated the importance of the ring substituents on their effective conjugation, evaluated by their UV absorption values. The corresponding apo-12′-carotenals 2 were devised to improve the conjugation effect of the para-phenolic radical with the polyene chain by the conjugated aldehyde group. Apo-12′-carotenals 2b and 2c without ortho-substituents exhibited superior antioxidant activities to their corresponding symmetrical carotenes 1 as well as β-carotene and apo-12′-β-carotenal in 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assays.