Crocetindial

Carotenoid radical ions: A laser flash photolysis study.[Pubmed:32980657]

J Photochem Photobiol B. 2020 Nov;212:112023.

Laser excitation of a single precursor, namely 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (HHEMP), has been used for generating the radical cations and radical anions of various carotenoids in methanol. In the presence of oxygen, laser excitation of HHEMP undergoes an efficient alpha-cleavage reaction (Norrish type I) to form acyl radicals, which react with O(2), in a nearly diffusion-controlled reaction, to form their corresponding strong oxidizing acylperoxyl radicals (RO(2)(*)) (E = ~1.1 V (v SHE)), which are capable of oxidizing almost all carotenoids. Under argon-saturated conditions and in the presence of strong base (0.01 M NaOH or tetrabutylammonium hydroxide (TBAOH)), the initially formed 2-hydroxy-2-propyl radical (ACH(*)), generated after LFP of HHEMP, is deprotonated to form the strong reducing acetone ketyl radical (AC(*-)) (E acetone/ AC(*-) = -2.1 V (v SHE)), which is capable of reducing all carbonyl-containing carotenoids. To validate this new proposed approach, retinal and beta-apo-8'-carotenal (APO), with known spectroscopic data, were investigated in methanol, acetonitrile and tetrahydrofuran (THF). In addition, the radical ions of newly investigated carotenoids, namely 4-oxo-beta-apo-15'-carotenoic acid (4-oxo-15'), Crocetindial, 4-oxo-beta-apo-10'-carotenoic acid ethyl ester (4-oxo-10') and 4-oxo-beta-apo-8'-carotenoic acid ethyl ester (4-oxo-8') have been reported. Moreover, the scope of this approach has been extended to investigate the radical ions of chlorophyll b.

The intramolecular charge transfer state in carbonyl-containing polyenes and carotenoids.[Pubmed:20825184]

J Phys Chem B. 2010 Sep 30;114(38):12416-26.

Numerous femtosecond time-resolved optical spectroscopic experiments have reported that the lifetime of the low-lying S(1) state of carbonyl-containing polyenes and carotenoids decreases with increasing solvent polarity. The effect becomes even more pronounced as the number of double bonds in the conjugated pi-electron system decreases. The effect has been attributed to an intramolecular charge transfer (ICT) state coupled to S(1), but it is still not clear what the precise molecular nature of this state is, and how it is able to modulate the spectral and dynamic properties of polyenes and carotenoids. In this work, we examine the nature of the ICT state in three substituted polyenes: Crocetindial, which contains two terminal, symmetrically substituted carbonyl groups in conjugation with the pi-electron system, 8,8'-diapocarotene-8'-ol-8-al, which has one terminal conjugated carbonyl group and one hydroxyl group, and 8,8'-diapocarotene-8,8'-diol, which has two terminal, symmetrically positioned, hydroxyl groups but no carbonyls. Femtosecond time-resolved optical spectroscopic experiments on these molecules reveal that only the asymmetrically substituted 8,8'-diapocarotene-8'-ol-8-al exhibits any substantial effect of solvent on the excited state spectra and dynamics. The data are interpreted using molecular orbital theory which shows that the ICT state develops via mixing of the low-lying S(1) (2(1)A(g)-like) and S(2) (1(1)B(u)-like) excited singlet states to form a resultant state that preferentially evolves in polar solvent and exhibits a very large ( approximately 25 D) dipole moment. Molecular dynamics calculations demonstrate that the features of the ICT state are present in approximately 20 fs.

A short and efficient synthesis of crocetin-dimethylester and crocetindial.[Pubmed:14604394]

J Org Chem. 2003 Nov 14;68(23):9126-8.

In this paper we describe an efficient six-step synthesis of crocetin-dimethylester that could be further reduced to a "four-step" synthesis through the use of in situ procedures. The simplicity of the whole process, the ready availability of starting materials, and the high overall yield render this strategy a very attractive synthesis of this very important compound, which is the key intermediate for the synthesis of several carotenoids and other polyene natural products.