Confirmation of the Structures of Lutein and Zeaxanthin

Abstract

A series of new esters of lutein (1a) have been prepared with the aim of confirming the structure of lutein via an X-ray crystal-structure analysis. Although well crystallized, only one of the derivatives, the (À)-(1R)-menthyl carbonate (1i) proved to be useful for a complete structure analysis. The same derivative of zeaxanthin (2a) also allowed its crystal structure to be determined. Both analyses represent the first successful X-ray crystal structure analyses of the most important xanthophylls. At the same time, they confirm both the constitution and absolute configuration of 1a and 2a that had been deduced earlier by classical methods.

Unravelling the chemical basis of the bathochromic shift in the lobster carapace; new crystal structures of unbound astaxanthin, canthaxanthin and zeaxanthin

“…We also report the room-temperature crystal structure of canthaxanthin, to compare directly with the Bart & MacGillavry (1968) room-temperature structure. The crystal structure of the bis[menthyl carbonate] derivative of RR-zeaxanthin has been reported previously (Linden et al, 2004), but to our knowledge the crystal structure of RS-zeaxanthin reported here is the first crystal structure of a free zeaxanthin. We will show that important variations of the various proposed colourtuning parameters have been achieved in a field where it was previously regarded as notoriously difficult to produce crystals.…”

“…Corresponding bond lengths and angles for RS-zeaxanthin, in general, also agree closely with those found for AXT and canthaxanthin. One difference is the C4-C5 bond length which is 1.513 (3) Å for RS-zeaxanthin, but ranges from 1.457 (4) to 1.480 (4) Å for the other five structures; however, the C4-C5 bond length in RS-zeaxanthin is similar to that in -carotene, which is 1.500 (7) Å (CSD entry CARTEN2; Allen, 2002) and the bis[menthyl carbonate] derivative of RRzeaxanthin (Linden et al, 2004) at 1.519 (7) and 1.512 (6) Å . This arises from the presence of the keto oxygen at the 4position in the AXT and canthaxanthin molecules, which leads to a shortening of the C4-C5 bond due to conjugation with the C5-C6 double bond.…”

“…However, the C4-C5 bond lengths for AXT and canthaxanthin are not as short as the conjugated single bonds of the polyene chains, which range from 1.425 (4) to 1.446 (2) Å for the AXT structures, 1.428 (3) to 1.452 (2) Å for canthaxanthin and 1.427 (3) to 1.449 (3) Å for RS-zeaxanthin, with shorter single bonds being found at the centre of the polyene chains. C6-C7 is also longer for RS-zeaxanthin at 1.492 (3) Å , than for the three AXT structures where this bond length varies from 1.462 (3) to 1.469 (4) Å , for canthaxanthin where this bond length has values of 1.471 (2) and 1.477 (2) Å and for -carotene at 1.468 (6) Å (CSD entry CARTEN2; Allen, 2002); for the bis[menthyl carbonate] derivative of RR-zeaxanthin (Linden et al, 2004) the C6-C7 distances for the crystallographically different ends are also shorter at 1.473 (7) and 1.468 (7) Å , although the difference is barely significant. In addition, the C5-C6-C7-C8 torsion angle of À74.9 (3) for RS-zeaxanthin (see Fig.…”

Interactions between canthaxanthin and lipid membranes — possible mechanisms of canthaxanthin toxicity

“…1. The latest published structures for lutein and zeaxanthin, based on crystallographic data, are given in [41], and for canthaxanthin in [42]. [41] (latest published) and canthaxanthin [42].…”

Exceptional molecular organization of canthaxanthin in lipid membranes.

“…Interestingly, all the effects were observed at much lower concentrations of the pigment in the lipid phase (below 1 mol%; in some cases as low as 0.05 mol%) than those of other xanthophylls such as lutein or zeaxanthin (for review on other carotenoids see: Gruszecki & Strzałka, 2005). This can be the consequence of different structures of these macular carotenoids themselves (Bart & MacGillavry, 1968;Linden et al, 2004). Apart from the functional keto-group in the ionone ring of canthaxanthin, the shape of the polyene chains in these xanthophylls differ to such an extent that this can affect their binding to the lipid membrane and the formation of molecular aggregates of xanthophyll molecules.…”