Synthesis of (3S,3'S)- and meso-stereoisomers of alloxanthin and determination of absolute configuration of alloxanthin isolated from aquatic animals.

In order to determine the absolute configuration of naturally occurring alloxanthin, a HPLC analytical method for three stereoisomers 1a-c was established by using a chiral column. Two authentic samples, (3S,3'S)- and meso-stereoisomers 1b and 1c, were chemically synthesized according to the method previously developed for (3R,3'R)-alloxanthin (1a). Application of this method to various alloxanthin specimens of aquatic animals demonstrated that those isolated from shellfishes, tunicates, and crucian carp are identical with (3R,3'R)-stereoisomer 1a, and unexpectedly those from lake shrimp, catfish, biwa goby, and biwa trout are mixtures of three stereoisomers of 1a-c.