Selective Preparation of Lutein Monomethyl Ethers.

Abstract

Crystalline 3-hydroxy-3[image]-methoxy-[alpha]-carotene (II) has been prepared by treatment of lutein (I) with methanol and hydrochloric acid. Proton magnetic resonance and infrared evidence support the structure II for this compound. 3-Methaxy-3[image]-hydroxy-[alpha]-carotene (V) was synthesized by nickel peroxide oxidation of lutein (I) to the previously unknown 3-hydroxy-3[image]-keto-[alpha]-carotene (III), followea by methylation with methyl iodide and silver oxide in dimethylformamide to 3-methoxy-3[image]-keto-[alpha]-carotene (IV) and finally borohydride reduction to V. The two lutein monomethyl ethers II and V could be separated chromatographically; II only was obtained in the pure crystalline state. Direct comparison between II, V, and the lutein monomethyl ether prepared by others by direct methylation of lutein (I) with methyl iodide and barium oxide in dimethylformamide-dimethyl-sulfoxide, revealed identity of the last named lutein ether with the allylic ether (II).