Process for the Preparation of Beta and Alpha Cryptoxanthin
The present invention relates to a process for converting lutein and/or lutein esters to (3R)-[beta]-cryptoxanthin and (3R,6'R)-[alpha]-cryptoxanthin, suitable for human consumption as dietary supplements, by employing safe and environmentally friendly reagents. (3R)-[beta]-Cryptoxanthin and (3R,6'R)-[alpha]-cryptoxanthin are two rare food carotenoids that are not commercially available and the former exhibits vitamin A activity. In the first synthetic step, commercially available lutein and/or lutein esters are transformed into a mixture of dehydration products of lutein (anhydroluteins) in the presence of a catalytic amount of an acid. The resulting anhydroluteins are then converted to (3R)-[beta]-cryptoxanthin (major product) and (3R,6'R)-[alpha]-cryptoxanthin (minor product) by heterogeneous catalytic hydrogenation employing transition elements of group VIII (Pt, Pd, Rh supported on alumina or carbon) in a variety of organic solvents under atmospheric pressure of hydrogen and at temperatures ranging from -15 DEG C. to 40 DEG C. Among these catalysts, Pt supported on alumina at 40 DEG C. in ethyl acetate provides the best yield of (3R)-[beta]-cryptoxanthin and (3R,6'R)-[alpha]-cryptoxanthin. Several homogeneous catalysts can also promote the regioselective hydrogenation of anhydroluteins to a mixture of (3R)-[beta]-cryptoxanthin and (3R,6'R)-[alpha]-cryptoxanthin in low to moderate yields. The catalysts may be transition metal complexes such as palladium acetylacetonate, Rh(Ph3P)3Cl (Wilkinson's catalyst), [(C6H11)3P[C8H12][C5H5N] Ir+PF6- (Crabtree catalyst), or [C8H12][(MePh2P)2]Ir+PF6-. Among these, Wilkinson catalyst converts anhydroluteins to (3R)-[beta]-cryptoxanthin and (3R,6'R)-[alpha]-cryptoxanthin in nearly quantitative yield. A novel feature of this invention is the regioselective hydrogenation of anhydroluteins while the highly conjugated polyene chain of these carotenoids remains intact.
KHACHIK FREDERICK [US]; LIU YUFA [US]; SHOWALTER HOLLY [US]
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