15,15 -Dehydro- 3-carotene

L-Theanine is the most abundant amino acid in tea flush. Volatiles produced by pyrolysis at 180°C of (A) L-theanine, (B) (-)-epigallocatechin gallate and (C) a mixture of (A) and (B) were examined. The procedure was the same as that reported earlier for the pyrolysis of 8-carotene. The results of the GC-MS analysis are shown in Figure 4. From L-theanine alone, a large amount of N-ethyl-formamide was formed, along with ethyl amine, propyl amine, 2-pyrrolidone, N-ethyl-succinimide and l-ethyl-3,4-dehydro-pyrrol idone. 

Dehydro-diepoxy-/J-carotene and mono-epoxy-a-carotene were ineffective in the same concentrations as were applied for other carotenoids (Table 3). 

Much less inhibition was found in the MCF7/MDR1 drug-resistant human breast cancer cell line in the presence of same carotenoids as were investigated earlier on the human MDR1 gene-transfected mouse lymphoma cells. As Table 5 shows the, rhodamine accumulation was enhanced only moderately from 1.1 to 2.2 fluorescence activity ratio, which means that the rhodamine uptake was enhanced from 10% to 120% in the human breast cancer cells. On the other hand, some carotenoids such as Zl-neoxanthin, mono-epoxy-a-carotene and 15,15-dehydro-diepoxy-/J-carotene were inactive (Table 5). 

The steric stability of acetylenic carotenoids has been investigated. " Stereoisomerization of a -trans- and 9,9 -di-cw-alloxanthin [7,8,7, 8 -tetra-dehydro-jS,/S-carotene-3,3 -diol (94)] and all-tran5-7,8,7, 8 -tetradehydro-astaxanthin (49) in the presence of I2 gave mainly the 9,9 -di-cw- and 9-mono-c/s-isomers, with none of the all-trans-form present in the pseudo-equilibrium mixture. All-trans-7,8-didehydroastaxanthin (48), however, gave a mixture of the 9-mono-c/s- and all-trans-isomers. 

Oxidation of diosphenols. Oxidation of 15,15 -dehydro-/8-carotene-3,4-dione... 

Diphenylamine-inhibited Epicoccum nigrum produces 3,4-dehydro-)3-carotene... 

The last vestige of the carotenoid polyene chain is left in dihydroactinidiolide (99), a compound formed on photochemical oxidation of )S-carotene, and recently isolated from tobacco " and tea aromas.Several syntheses of (99) have been reported, as well as of the related natural products actini-diolide (3,4-dehydro and loliolide (100). ... 

The ester, ethyl p-apo-8 -carotenate (17 X = OEt) corresponding to p-apo-8 -carotenal is an important colourant which has been referred to earlier. Technically it has been derived from the Cjt compound, dehydro-p-CjT-carotenal, an intermediate in the synthesis of p-apo-8 -carotenal (Scheme 14b) by Wittig reaction with the phosphoran formed from the triphenylphosphonium salt of ethyl o-bromopropionate with sodium ethoxide (ref. 5,p459). The resultant dehydro compound was partially reduced with Lindlar catalyst and the product then themally isomerised to ethyl p-apo-8 -carotenate as shown in Scheme 17. 

Synthesis of carotinoids via sulfones. FischU and Mayer have developed a synthesis of carotinoids based on the fact that allylic aryl sulfones in the presence of base readily eliminate arylsulfinic acid with formation of a conjugated double bond. An example is the synthesis of 15,15 -dehydro- 3-carotene... 

Dehydro-r fro-carotene (48) is an example of a re/ro-carotene and has been synthesized via the C20 + C20 = C40 strategy with vitamin A (29) as starting material [8]. The Wittig reaction of the phosphonium salt of vitamin A (30) with the 4-acetoxy derivative of retinal (31), synthesized by reaction of retinal (32) with NBS/AcOH, gave isocryptoxanthin acetate (33). This compound was transformed with HBr into dehydro-re/ro-carotene (48), in an overall yield of 30% (Scheme 7). 

Dehydro r rr(9-carotene (48) was also synthesized via the diol 34, an intermediate from the synthesis of isozeaxanthin (129). The diol 34 was transformed into 48 in low yield by the Whiting reaction with UAIH4 [9] (Scheme 8). 

N-Bromosuccinimide added at -50° to a stirred soln. of dehydro-retro-carotene in chloroform-acetic acid, stirred 7 min., N,N-diethyIaniline added, stirring continued 2 hrs. at 0°, the crude product stirred 2 hrs. at 40° with benzene and methanolic 10%-KOH, the resulting crude isozeaxanthin dissolved in benzene, Al-isopropoxide and acetone added, stirred and refluxed 16 hrs. under Ng -> canthaxanthin. Y 74%. F. e. s. J. D. Surmatis et al., Helv. 55, 974 (1970). 

Phytoene an aliphatic, colorless hydrocarbon carotenoid, M, 544. P. is a polyisoprenoid containing six branch methyl groups, two terminal isopropyli-dene groups and nine double bonds, three of them conjugated. Only the A double bond has cis configuration. Biosynthetically, P. is derived from two molecules of geranylgeranyl pyrophosphate, and it serves as a C40-starter molecule in the biosynthesis of other carotenoids phytofluene, carotene, neurosporene and lycopene are formed by the stepwise dehydro-... 

An interesting isocratic solvent system, 22/71/4/2/1 DCM/acetonitrile/ methanol/water/propionic acid, was used to elute carotenoids, retinol, retinal, and their dehydro analogs (21 compounds total) on a Cig column (A = 352nm or 450ran) from fish serum and eggs [771]. A table was generated that contained retention times and W values for all compounds. Elution was complete in just under 60 min, with retinyl palmitate and a- and j -carotene the only analytes with retention times of >20 min. Standards of 2pg/mL were used and easily detected. Baseline resolution was not achieved between all analyte pairs. 

Carotenes I, II and III (cf. Formulas 3.119-3.122) are intermediary or precursor compounds which, in biosynthesis after repeated dehydro-genizations, provide lycopene (IV see a textbook of biochemistry). Lycopene is the red color of the tomato (and also of wild rose hips). In yellow tomato cultivars, lycopene precursors are present together with 3-carotene (Table 3.56). 

---