Bicyclic Carotenoids

Bicyclic Carotenoids. A major pigment of the bacterium Rhizobium lupini, 2,3,2, 3 -di-/rans-tetrahydroxy-/3,j8-caroten-4-one (9), is the first natural carotenoid to be described with oxygen substituents at positions 2, 3, and 4 of the ring. Also present were 2,3,2 (or 3 )-trihydroxy-/3, -caroten-4-one, (10) or (11), 

Kleinig, W. Heumann, W. Meister, and G. Englert, Helv. Chim. Acta, 1977, 60, 254. 

A minor carotenoid of the alga Coccolithus huxleyi has been identified as 3 -desacetyl-I9 -n-hexanoyloxyfucoxanthin [5,6-epoxy-19 -n-hexanoyloxy-3,3 .5 -trihydroxy-6, 7 -didehydro-5,6,7,8,5, 6 -hexahydro-/3,/S-caroten-8-one (14)]. Two 

C-5 epimers of 6,7-didehydro-5,6,5, 6 -tetrahydro-)3,/3-carotene-3,5,3 5, 6 -pentol (15), isolated as minor constituents of a sample of neoxanthin [5, 6 -epoxy-6,7-didehydro-5,6,5, 6 -tetrahydro-j8,j8-carotene-3,5,3 -triol (16)] from Trollius europaeus, may be artefacts. In Sarcina lutea, sarcinaxanthin [2,2 -bis-(4- 

Buchecker, S. Liaaen-Jensen, G. Borch, and H. W. Siegelman, Phytochemistry, 1976, 15, 1015. 

Bicyclic Carotenoids.— The absolute stereochemistry of a-carotene (4) has been determined by Eugster and co-workers by relating a-ionone to derivatives of manool and ambrein. Natural (-t- )-a-carotene (4) was synthesised from (-I- )-a-ionone and related by o.r.d. to several other carotenoids with this chiral centre,  

Yokoyama et al. have isolated a series of seco-carotenoids from Rutaceae. Semi-a-carotenone (3) was shown by c.d. studies to have the same absolute stereochemistry as a-carotene. The other examples isolated were semi-j -carotenone (33), jS-carotenone (34) and triphasiaxanthin (35).  

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

Szabolcs and A. Ronai, Acta Chim. Acad. Sci., Hung.., 1969, 61, 309. 

---

Carotenoid distribution in fungi, nonphotosynthetic organisms, are apparently capricious, but they usually accumulate carotenes, mono- and bicyclic carotenoids, and lack carotenoids with e rings. Plectaniaxanthin in Ascomycetes and canthaxan-thin in Canthardlus cinnabarinus have been found. ... 

Bicyclic Carotenoids. Re-investigation of the carotenoids of Anacystis nidulans has confirmed the presence of /3,)8-carotene-2,3,3 -triol (6), and the previously unknown )8,j8-carotene -2,3,2, 3 -tetrol (7) was also isolated. These compounds are considered to be identical with caloxanthin and nostoxanthin, for which allenic structures have previously been suggested. The main carotenoid of Coccolithus... 

Carotenoids are tetraterpenes derived from a symmetrical C40 skeleton. Carotenoids can be classified into two great groups carotenes, which are strictly hydrocarbons, and xanthophylls, derived from the former that contain oxygenated functions. Stracturally, the carotenoids may be acyclic (e.g., lycopene) or contain a ring of five or six carbons at one or both ends of the molecule (e.g., /3-carotene). Figure 10.1 shows the stmcture and the system of numbering using lycopene and /3-carotene as models of acyclic and bicyclic carotenoids respectively. Stractures of some representative carotenes and xanthophylls, commonly found in fruits are also illustrated. 

New Structures and Stereochemistry Bicyclic Carotenoids Monocyclic Carotenoids Acyclic Carotenoids Apocarotenoids Degraded Carotenoids Synthesis and Reactions Carotenoids Retinoids... 

The effect of cis double bonds in the polyene chain should be pointed out. In bicyclic carotenoids such as diatoxanthin (41) mono-d.v configuration at A 9,9, 13,13 and 15 reverses the sign of the Cotton effect 20,36,69,126,136). Consequently CD spectra are sensitive to impurities of geometrical isomers. The CD band in the so-called cw-peak region... 

Zeinoxanthin (3/ ,6 / )-/3,e-Caroten-3-ol Bicyclic, monohydroxy-carotenoid Inactive... 

Since the initial reports of the C-P-Q triads, a number of other molecules of the D-D -A or D -D-A types have been described. Triad 12, prepared by Wasielewski and coworkers, is a relative of the C-P-Q series in which the secondary donor is an aniline derivative (D), rather than a carotenoid [63]. The bicyclic bridges were introduced in order to add rigidity to the system. The fluorescence lifetime of the porphyrin moiety of 12 was found to be <30ps. This result is consistent with rapid electron transfer to the quinone to yield D-P+-QT. This result was confirmed by transient absorption measurements. The absorption results also revealed that this intermediate charge separated state decays with a rate constant of 1.4 x 1010 s-1 to a final charge separated state D+-P-Qr. Thus, the decay pathways are similar to those shown in Fig. 3 for the C-P-Q triads. This final state has a lifetime of 2.45 ps in butyronitrile (which is similar to that found for 4 in acetonitrile) [44], and is formed with a quantum yield of about 0.71. Thus, the efficiency of the transfer analogous to step 4 in Fig. 3 for this molecule is also about 0.71. 

The naphthoquinone and benzoquinone moieties are linked by a saturated, rigid bicyclic ring system, and the carotenoid and diquinone species are... 

The hula twist mechanism (HT, Fig. 2.3B), first validated with carotenoids, is not consistent with the time-scale of photoisomerization of chromoproteins since CTI of the retinal chromophore, which is inserted deep inside the protein, necessitates a major reorganization of the peptide molecular framework. Therefore, a new volume-conserving mechanism, called bicyclic pedal (BP, Fig. 2.3C), was proposed. In fact, all these mechanisms are still a topic of discussion since chromoprotein photo-intermediates highlighted by recent studies do not confirm this hypothesis. In particular, several photo-products of the retinal Schiff base in the... 

The formation of the normally present cyclic carotenoids is Inhibited. The transformation of the acyclic lycopene to the monocyclic gamma-carotene Is partially inhibited and further cyclizatlon to the bicyclic beta-carotene is totally Inhibited. However, when the treatment of the entire tree which Is sprayed with 2,000 ppm MPTA Is conducted preharvest at the fully mature stage of fruit development [2], the carotenoid composition of the endocarp reflects a net synthesis of the cyclic pigments and differs from the pattern seen in the peel as shown in Table II. 

A 5 mm diameter circular mycelial mat from the 10 ppm DCPTA media [1st transfer] was transferred to media containing 0 ppm DCPTA and allowed to further develop for 3 days to about 35 cm in diameter. Examination of the latter mycelial mat clearly show no evidence of any carryover of DCPTA from the initial media. The carotenoid composition of the first transfer show the usually present bicyclic beta-carotene, not the acyclic lycopene, as the main pigment, similar to the pattern normally found in the mycelia of the mold. However, there was a ten-fold increase in the amount of beta- and... 

Fig. 7.2 Classification and structure of carotenoids (a) lycopene - acyclic hydrocarbon (b) 7-carotene - monocyclic hydrocarbon (c) /3-carotene - bicyclic hydrocarbon (d) lutein - bicyclic xanthophyll.

With reference to the carotenoid skeleton, illustrated by the bicyclic p,p-carotene (3), and the aliphatic tridecaene spirilloxanthin (166), three categories of (Z)-carbon-carbon double bonds may be distinguished [1] ... 

---