Substitution carotenoids

Liu DZ, Szulczewski GJ, Kispert LD, Primak A, Moore TA, Moore AL, and Gust D. 2002. A thiol-substituted carotenoid self-assembles on gold surfaces. Journal of Physical Chemistry B 106(11) 2933-2936. 

Part IV Synthesis of Acetylenic, Allenic and In-chain Substituted Carotenoids... 

S. Tretiak, V. Chernyak and S. Mukamel, Two-dimensional real-space analysis of optical excitations in acceptor-substituted carotenoids,/ Am. Chem. Soc., 1997, 119, 11408-11419. 

Chemical shift considerations have also proved adequate for assignment of geometrical isomerism in the phytoene (21) series 115), for configurational assignment of the hydroxylated isopropylidene end group in decaprenoxanthin (8) and lycoxanthin (22) after allylic oxidation to the corresponding aldehydes 133, 156), as well as for analysis of 13-cw and 3-trans mixtures of 20-substituted carotenoids related to reniera-purpurin-20-al (23) 49). 

The sensitivity of CD spectra to steric alterations in the polyene chain is also reflected by the CD of in-chain substituted carotenoids such as loroxanthin (of unknown configuration), which is the 19 -hydroxy derivative of lutein (14) (59). In-chain substituents are known to influence the geometry of the polyene chain 49, 54). 

Chae, C., P.-S. Song, J. E. Johansen, and S. Liaaen-Jensen Linear dichroic spectra of cross-conjugated carotenals and configurations of in-chain substituted carotenoids. J. Amer. Chem. Soc. 99, 5609 (1977). 

Two examples are mentioned here to illustrate how IR spectroscopy can be used to obtain structural information about SAMs The molecular structure of a thiol-substituted carotenoid (see Sect. 4.3.7) was investigated by IR spectroscopy. Comparison of the IR spectrum of the carotenoid in the KBr matrix with that in the SAM shows the peak frequencies to be slightly higher... 

A number of keto-carotenoids have been prepared from the bis-phosphonium salt (130) and substituted Cjs-aldehydes, the keto-functions... 

Careful empirical selection of the expression platform for carotenogenesis has included selection of the best strains for stability and degree of accumulation and the selection of compatible drug-resistance combinations and low copy number polycistronic plasmids to enhance product accumulation by decrease of metabolic burden." 5 Matthews and Wurtzel discussed culture and induction conditions - that have been explored in most studies. Most efforts to engineer carotenoid biosynthesis in E. coli focused on the genes and enzymes of the pathway and had a modest effect on improved accumulation. For example, substitution and over-expression of a GGPPS that uses IPP directly (discussed in... 

Owing to their chemical structure, carotenes as polyterpenoids are hydrophobic in nature (Britton et al., 2004). Therefore, as it might be expected, the carotenes are bound within the hydrophobic core of the lipid membranes. Polar carotenoids, with the molecules terminated on one or two sides with the oxygen-bearing substitutes, also bind to the lipid bilayer in such a way that the chromophore, constituted by the polyene backbone is embedded in the hydrophobic core of the membrane. There are several lines of evidence for such a localization of carotenoids with respect to the lipid bilayers. 

ESEEM measurements of perdeuterated all-trany-p-carotene imbedded in activated Cu-substituted MCM-41 molecular sieve revealed (Gao et al. 2005) that two deuterons of the carotenoid interact with the Cu2+ at a distance of 3.3 A. Possible double bonds of P-carotene with one deuterium at each carbon that could interact with Cu are C7=C8, CH-C12, 05=05, 02 - C1T, and C8 =C7. 

Carotenoids incorporated in metal-substituted MCM-41 represent systems that contain a rapidly relaxing metal ion and a slowly relaxing organic radical. For distance determination, the effect of a rapidly relaxing framework Ti3+ ion on spin-lattice relaxation time,and phase memory time, Tu, of a slowly relaxing carotenoid radical was measured as a function of temperature in both siliceous and Ti-substituted MCM-41. It was found that the TM and 7) are shorter for carotenoids embedded in Ti-MCM-41 than those in siliceous MCM-41. 

Lawrence, J., A. L. Focsan et al. (2008). Pulsed ENDOR studies of carotenoid oxidation in Cu(II)-substituted MCM-41 molecular sieves. J. Phys. Chem. B 112 1806-1819. 

Carotenoids are hydrophobic molecules and thus are located in lipophilic sites of cells, such as bilayer membranes. Their hydrophobic character is decreased with an increased number of polar substitutents (mainly hydroxyl groups free or esterified with glycosides), thus affecting the positioning of the carotenoid molecule in biological membranes. For example, the dihydroxycarotenoids such as LUT and zeaxanthin (ZEA) may orient themselves perpendicular to the membrane surface as molecular rivet in order to expose their hydroxyl groups to a more polar environment. In contrast, the carotenes such as (3-C and LYC could position themselves parallel to the membrane surface to remain in a more lipophilic environment in the inner core of the bilayer membranes (Parker, 1989 Britton, 1995). Thus, carotenoid molecules can have substantial effects on the thickness, strength, and fluidity of membranes and thus affect many of their functions. 

The pyridazin-3-ones are interesting because they include herbicides having two different modes of action, distinguished only by small changes in substitution pattern. Thus pyrazon (8) (61GEP1105232) is a photosynthesis inhibitor, while other discussed later are carotenoid biosynthesis inhibitors. The pyridazin-3-one ring is constructed by condensation of phenyl-hydrazine with 3,4-dichloro-2,5-dihydro-5-hydroxyfuran-2-one (9), in turn produced by chlorination of furan-2-carbaldehyde. Amination of (10) then occurs exclusively at the 5-position to give pyrazon (Scheme 4). 

Substitution of a trifluoromethyl group in the 3-position of the benzene ring and alkylation of the 4-amino group, as in norflurazon (16) (69FRP1575643), turns the pyridazin-3-ones into inhibitors of carotenoid biosynthesis. A similar substitution pattern occurs in fluridone (17) (74GEP2537753). The long-established l,2,4-triazol-3-ylamine, known as amitrole, and... 

Not all Cl8 (ODS) columns are manufactured in the same way. As such, substitution of other columns for those listed in the above methods will probably yield inferior results. For a detailed explanation of column and solvent effects on the separation of carotenoids, see Epler et al. (1992). 

Isoprenoid acyclic polyene carbocations with 6, 14, and 18 tt-electrons were synthesized.138 Considering also previous data for carotenoid dications, an equation correlating /.max (ranging from 400 to 1100 nm) and the number of sp2 hybridized carbon atoms in the dication was developed. Dication (67) and an analogue with a different alkyl substitution pattern were prepared as PF6 salts.139 These dications form... 

Two phytoene desaturase herbicides have been introduced since 2000 picolina-fen (Pico ) [182], introduced in 2001 by BASF, and beflubutamid [183], introduced in 2003 by Ube Industries. The primary mode of action of picolinafen and beflutamid is interference of carotenoid biosynthesis at the phytoene desaturation level, causing bleaching of the plant affected. As in previously developed phytoene desaturase herbicides, a meta-substituted trifluoromethylphenyl group is key for activity in this class of herbicides, pointing to the need for a lipophilic and electron-withdrawing group at this position of the molecule. 

Fig. 21. Structure of the polarized carotenoids where R represents the substitution...

The synthetic principle of olefinating an a,co-bisfunctional synthon A, representing the later molecular centre of the carotenoid, with two reaction partners B, the future molecular ends, can easily be described by the equation A + 2B -> B—A—B. This method was used by Mayer et al.265> in the synthesis of rhodoxanthin 550, a ketonic carotenoid, which was isolated for the first time from the red berrys of the yew-tree Taxus baccata. The authors describe the conversion of two equivalents of the stable phosphorane 548 with one equivalent of the C12-dialdehyde 549 265) (Scheme 93). The analogous reaction of crocetindial 552 with substituted benzylidenephospho-ranes such as 551 gives carotenoids such as isorenieratene 553266,267) and related compounds 266> (Scheme 93). Condensation of the phosphoranes 554 and 555 with the Cjo-dialdehyde 539 yields carotenoids of the dihydro type 556 268) and such like 557 269), respectively (Scheme 93). 

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