Carotenoids with two chromophores: carotenoid retinoates.

In this study, carotenoid retinoates are described for the first time. The preparation was achieved by the azolide method. Various sec carotenols reacted with N-retinoylimidazol in the presence of catalytic amounts of sodium hydride.

Reconstitution of gloeobacter rhodopsin with echinenone: role of the 4-keto group.

In previous work, we reconstituted salinixanthin, the C(40)-carotenoid acyl glycoside that serves as a light-harvesting antenna to the light-driven proton pump xanthorhodopsin, into a different protein, gloeobacter rhodopsin expressed in Escherichia coli, and demonstrated that it transfers energy to the retinal chromophore [Imasheva, E. S., et al.

X-ray crystal structure and time-resolved spectroscopy of the blue carotenoid violerythrin.

Violerythrin, a blue-colored carotenoid, has been investigated by X-ray crystallography and steady-state and ultrafast time-resolved absorption spectroscopy. The X-ray crystal structure of violerythrin shows that the molecule is nearly planar with the terminal rings positioned in the s-trans conformation. The steady-state and time-resolved spectroscopic data of violerythrin do not differ significantly from those of other carbonyl carotenoids with long (N > 10) pi-electron conjugated chains.

X-ray crystal structures of diacetates of 6-s-cis and 6-s-trans astaxanthin and of 7,8-didehydroastaxanthin and 7,8,7',8'-tetradehydroastaxanthin: comparison with free and protein-bound astaxanthins.

The crystal structures of the 6-s-cis [s-cis-(1)] and 6-s-trans [s-trans-(1)] conformers of the diacetates of astaxanthin (AXT) and those of (3S,3'S)-7,8-didehydroastaxanthin [(3S,3'S)-3,3'-dihydroxy-7,8-didehydro-beta,beta-carotene-4,4'-dione (2)] and (3S,3'S)-7,8,7',8'-tetradehydroastaxanthin [(3S,3'S)-3,3'-dihydroxy-7,8,7',8'-tetradehydro-beta,beta-carotene-4, 4'-dione (3)] are reported. The conformations of these four molecules vary in particular with the angle of twist of the end rings out of the plane of the polyene chain; for s-cis-(1), the end rings are twisted out of the plane of the polyene chain by an angle of -49.0 (5)degrees , and the conformation is therefore similar to that found for unesterified AXT as well as for the carotenoids, canthaxanthin and beta,beta-carotene.

Two polymorphs of 20-desmethyl-beta-carotene.

Two polymorphs of 20-desmethyl-beta-carotene (systematic name: 20-nor-beta,beta-carotene), C(39)H(54), in monoclinic and triclinic space groups, were formed in the same vial by recrystallization from pyridine and water. Each polymorph crystallizes with the complete molecule as the asymmetric unit, and the two polymorphs show differing patterns of disorder. The beta end rings of both polymorphs have the 6-s-cis conformation, and are twisted out of the plane of the polyene chain by angles of -53.

13-cis-Beta,beta-carotene and 15-cis-beta,beta-carotene.

13-cis-Beta,beta-carotene, C(40)H(56), crystallizes with a complete molecule in the asymmetric unit, whereas 15-cis-beta,beta-carotene, also C(40)H(56), has twofold symmetry about an axis through the central bond of the polyene chain. The polyene methyl groups are arranged on one side of the polyene chains for each molecule and the 6-s-cis beta end groups, with the cyclohexene rings in half-chair conformations, are twisted out of the planes of the polyene chains by angles ranging from 41.37 (17) to 52.

Studies on the mechanism of the Carr-Price blue colour reaction.

The reaction of retinoids (retinol, retinyl acetate and anhydroretinol) with Brønsted acids was studied as a model system for the Carr-Price reaction. The anhydroretinylic cation was characterised by VIS and 2D NMR spectroscopy, including an estimate of the charge distribution and region of bond inversion, observed in a mixture of identified E/Z isomers. Products obtained by quenching with NaOMe-MeOH were identified by HPLC and MS.

Longer polyenyl cations in relation to soliton theory.

The carotene-like polyenes decapreno-beta-carotene (C50), C54-beta-carotene (C54, first synthesis) and dodecapreno-beta-carotene (C60) with 15, 17 and 19 conjugated double bonds, respectively, were synthesized by double Wittig reactions. Introduction of a leaving group in allylic position failed, and cations were obtained by hydride elimination effected by i) triphenylcarbenium tetrafluoroborate-d15, prepared by a new method, or ii) treatment with trifluoroacetic acid-d. Deuterated reagents were employed for product analysis by 1H NMR.

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

The crystal structures of the unbound carotenoids, synthetic astaxanthin (3S,3'S:3R,3'S:3R,3'R in a 1:2:1 ratio), canthaxanthin and (3R,3'S, meso)-zeaxanthin are compared with each other and the protein bound astaxanthin molecule in the carotenoprotein, beta-crustacyanin. Three new crystal forms of astaxanthin have been obtained, using different crystallization conditions, comprising a chloroform solvate, a pyridine solvate and an unsolvated form. In each structure, the astaxanthin molecules, which are similar to one another, are centrosymmetric and adopt the 6-s-cis conformation; the end rings are bent out of the plane of the polyene chain by angles of -42.

Torularhodin and torulene are the major contributors to the carotenoid pool of marine Rhodosporidium babjevae (Golubev).

A carotenoid-producing yeast strain, isolated from the sub-arctic, marine copepod Calanus finmarchicus, was identified as Rhodosporidium babjevae (Golubev) according to morphological and biochemical characteristics and phylogenetic inference from the small-subunit ribosomal RNA gene sequence. The total carotenoids content varied with cultivation conditions in the range 66-117 microg per g dry weight. The carotenoid pool, here determined for the first time, was dominated by torularhodin and torulene, which collectively constituted 75-91% of total carotenoids under various regimes of growth.

On the structure of carotenoid iodine complexes.

Previous work on carotenoid-iodine complexes is briefly reviewed. The formation of iodine complexes of beta,beta-carotene and of (3R,3' R )-beta,beta-carotene-3,3'-diol (zeaxanthin) has been studied by modern methods including UV/VIS/NIR, IR MS, EPR, ENDOR and NMR (1H, 1H-1H COSY, TOCSY, 2D ROESY, 1H-13C HSQC and 1H-13C HMBC) spectroscopy, and chemical reactions monitored by HPLC, TLC and spectral analysis (VIS, MS, 1H NMR). beta,beta-Carotene formed a solid complex C40H56 x 4I with iodine in hexane and a solvent complex with lambdamax 1010 nm in chlorinated solvents.

Nucleophilic reactions of charge delocalised carotenoid mono- and dications.

In the present study insight was gained on the larger complexity of cationic mixtures of diaryl (phi,phi-carotene, isorenieratene) and aliphatic (psi,psi-carotene, lycopene) carotenes, prepared by reaction with BF3-etherate, compared with beta,beta-carotene. Chemical reactions of the mono- and dications prepared in situ from the allylic carotenols beta,beta-caroten-4-ol (isocryptoxanthin) and beta,beta-carotene-4,4'-diol (isozeaxanthin), and from isorenieratene and lycopene were investigated using selected O, N and S nucleophiles; water, methanol, azide and thioacetate. In total 22, including 18 new, neutral carotenoid products were isolated and identified by VIS, MS and NMR (in part) spectroscopy.

Delocalized carotenoid cations in relation to the soliton model.

A series of charge-delocalized carotenoid mono- and dications have been prepared by treatment of selected carotenoids with Brønsted and Lewis acids. The detailed structures of the carbocations were established by NMR studies in the temperature range from -10 to -20 degrees C. The general strategy for structure elucidation by NMR of several cationic components in a mixture is outlined.

Protonated canthaxanthins as models for blue carotenoproteins.

It has been suggested that astaxanthin (3,3'-dihydroxy-beta,beta-carotene-4,4'-dione) in the carotenoprotein alpha-crustacyanin occurs in the diprotonated form. As a model system for protonated astaxanthin in [small alpha]-crustacyanin the reactions of canthaxanthin ([small beta],[small beta]-carotene-4,4[prime or minute]-dione) with Bronsted acids (CF(3)COOH and CF(3)SO(3)H) and the Lewis acid BF(3)-etherate have been investigated. Structures of C-5 protonated, C-7 protonated, enolised O-4 protonated and O-4,4[prime or minute], C-7 triprotonated canthaxanthin have been established by VIS-NIR and NMR spectroscopy.

The charge delocalised beta,beta-carotene dication--preparation, structure elucidation by NMR and reactions with nucleophiles.

The reaction between beta,beta-carotene and BF3-etherates has been investigated, leading to structural elucidation of the blue product, formed in appropriate organic solvents, as a symmetrical charge delocalised dication (lambda(max) 985 nm at room temperature in CHCl3) with considerable stability. The reaction, monitored by EPR studies at -25 degrees C, occurred via free radical intermediates. A C40H56BF3 intermediate was captured by EIMS.

Structure elucidation of polyene systems with extensive charge delocalization-carbocations from allylic carotenols.

[structure: see text] The structures of two diastereomeric cations, readily prepared from beta, beta-caroten-4-ol (1) by treatment with trifluoroacetic acid, have been determined by NIR and NMR spectroscopy, resulting in the complete structure elucidation of the most extensively delocalized carbocations so far described. Higher partial charge was observed toward the center of the polyene chain (larger filled red circles). Bond reversion occurs in the central region of the molecule.

New C(40)-carotenoid acyl glycoside as principal carotenoid in Salinibacter ruber, an extremely halophilic eubacterium.

The principal (>96% of total) carotenoid in the novel, extremely halophilic eubacterium Salinibacter ruber, here called salinixanthin (1), has been assigned the structure (all-E,2'S)-2'-hydroxy-1'-[6-O-(13-methyltetradecanoyl)-beta-D-glycopyranosyloxy]-3',4'-didehydro-1',2'-dihydro-beta,psi-caroten-4-one by spectrometric (vis, EIMS, (1)HNMR, CD, GCMS) and chemical methods.