Natural occurrence of enantiomeric and meso-astaxanthin 4. Ex shrimps ( Pandalus borealis)

Abstract

1. 1. The quantitative carotenoid composition of shells of the common northern circumpolar shrimp Pandalus borealis (Crustaceae Malacostraca, order Decapoda) (i) fresh frozen, (ii) boiled and (iii) processed shrimp meal, is reported. Astaxanthin, present as the free diol, mono-and diester with higher fatty acids, was identified by co-chromatography with authentic standards, conversion to astacene and spectral criteria (electronic-, mass- and CD spectra). 2. 2. By conversion to its diester with (−) camphanic acid astaxanthin from unboiled shells was shown by HPLC analysis to consist of the (3S, 3′S), ( 3R,3′R; meso) and ( 3R,3′R) isomers in ratio 25:52:23. 3. 3. Natural astaxanthin monoester was by similar procedure found to consist of the ( 3S)-ol and the ( 3R)-ol in ration 47:53, Saponification of the monoester in the absence of oxygen provided astaxanthin, shown by the above HPLC method to consist of the ( 3S,3′S), ( 3R,3′S;meso) and ( 3R,3′R) isomers in ration 17:50:33. Natural astaxanthin diester provided astaxanthin, containing the optical isomers ( 3S,3′S), ( 3R,3′S; meso) and ( 3R,3′R) in ratio 12:46:43. 4. 4. The strongly racemized nature of astaxanthin and its monoester was confirmed by the chiroptical data. The CD data for the natural astaxanthin diester confirmed a high degree of racemization with some preference for R- configuration ( ca, 13% optical purity ). 5. 5. The data suggest some preference for 3R- configuration of astaxanthin in the in vivo acylation reaction.