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Misao Mizuno, Keita Sato, Takahiro Yamashita, Kazumi Sakai, Yasushi Imamoto, Yumiko Yamano, Akimori Wada, Hideyo Ohuchi, Yoshinori Shichida, and Yasuhisa Mizutani, Chromophore Structure in an Inactive State of a Novel Photosensor Protein Opn5L1: Resonance Raman Evidence for the Formation of a Deprotonated Adduct at the 11th Carbon Atom, The Journal of Physical Chemistry B, 127(10), 2169-2176, March 16, 2023, © 2023 American Chemical Society. DOI: 10.1021/acs.jpcb.2c08780, Opsins are photosensitive G protein-coupled receptor proteins and are classified into visual and nonvisual receptors. Opn5L1 is a nonvisual opsin that binds all-trans retinal as a chromophore. A unique feature of Opn5L1 is that the protein exhibits a photocyclic reaction upon photoexcitation. Determining the chromophore structures of intermediates in the photocycle is essential for understanding the functional mechanism of Opn5L1. A previous study revealed that a long-lived intermediate in the photocycle cannot activate the G protein and forms a covalent bond between the retinal chromophore and a nearby cysteine residue. However, the position of this covalent bond in the chromophore remains undetermined. Here, we report a resonance Raman study on isotopically labeled samples in combination with density functional theory calculations and reveal that the 11th carbon atom of the chromophore of the intermediate forms a covalent linkage to the cysteine residue. Furthermore, vibrational assignments based on the isotopic substitutions and density functional theory calculations suggested that the Schiff base of the intermediate is deprotonated. The chromophore structure determined in the present study well explains the mechanism of the photocyclic reaction, which is crucial to the photobiological function of Opn5L1.

Photosynthetic organisms adapt to a variety of light conditions. Codium fragile, a macrosiphonous green alga, binds a unique carbonyl carotenoid, siphonaxanthin, to its major photosynthetic light-harvesting complexes, allowing it to utilize dim blue-green light for photosynthesis. Here, we describe the absolute chemical structure of a novel siphonaxanthin biosynthetic precursor, 19-deoxysiphonaxanthin, that accumulates specifically in the photosynthetic antenna only when cultivated under blue-green light. The action spectra of pigment accumulation suggest that siphonaxanthin biosynthesis is regulated by a specific wavelength profile. The results provide clues to a new acclimation mechanism to withstand hours of intense light at low tide and why siphonous algae have been growing invasively on the world's coasts for more than a century.

Development of efficient photocatalysts with a wide spectral range for the photocatalytic hydrogen evolution reaction (HER) is a promising way to address the current energy and environmental crises.

beta-Apocarotenoids are the cleavage products of beta-carotene. They are found in plants, carotenoid-containing foods, and animal tissues. However, limited information is available regarding the health benefits of beta-apocarotenoids. Here, we prepared seco-type beta-apocarotenoids through the chemical oxidation of beta-carotene and investigated their anti-inflammatory effects against activated macrophages. Oxidation of beta-carotene with potassium permanganate produced seco-beta-apo-8'-carotenal, in which one end-group formed an "open" beta-ring and the other was cleaved at the C-7',8' position. In lipopolysaccharide-stimulated murine macrophage-like RAW264.7 cells, seco-beta-apo-8'-carotenal inhibited the secretion and mRNA expression of inflammatory mediators such as nitric oxide, interleukin (IL)-6 and IL-1 beta, and monocyte chemoattractant protein-1. Furthermore, seco-beta-apo-8'-carotenal suppressed phosphorylation of c-Jun N-terminal kinase and the inhibitor of nuclear factor (NF)-kappa B as well as the nuclear accumulation of NF-kappa B p65. Notably, since seco-beta-apo-8'-carotenal exhibited remarkable anti-inflammatory activity compared with beta-apo-8'-carotenal, its anti-inflammatory action could depend on the opened beta-ring structure. These results suggest that seco-beta-apo-8'-carotenal has high potential for the prevention of inflammation-related diseases.

Carotenoids (Cars) exhibit two functions in photosynthesis, light-harvesting and photoprotective functions, which are performed through the excited states of Cars. Therefore, increasing our knowledge on excitation relaxation dynamics of Cars is important for understanding of the functions of Cars. In light-harvesting complexes, there exist Cars functioning by converting the π-conjugation number in response to light conditions. It is well known that some microalgae have a mechanism controlling the conjugation number of Cars, called as the diadinoxanthin cycle; diadinoxanthin (10 conjugations) is accumulated under low light, whereas diatoxanthin (11 conjugations) appears under high light. However, the excitation relaxation dynamics of these two Cars have not been clarified. In the present study, we investigated excitation relaxation dynamics of diadinoxanthin and diatoxanthin in relation to their functions, by the ultrafast fluorescence spectroscopy. After an excitation to the S

Shikonin derivatives are red naphthoquinone pigments produced by several boraginaceous plants, such as Lithospermum erythrorhizon. These compounds are biosynthesized from p-hydroxybenzoic acid and geranyl diphosphate. The coupling reaction that yields m-geranyl-p-hydroxybenzoic acid has been actively characterized, but little is known about later biosynthetic reactions. Although 3″-hydroxy-geranylhydroquinone produced from geranylhydroquinone by CYP76B74 has been regarded as an intermediate of shikonin derivatives, the next intermediate has not yet been identified. This study describes a novel alcohol dehydrogenase activity in L. erythrorhizon cell cultures. This enzyme was shown to oxidize the 3″-alcoholic group of (Z)-3″-hydroxy-geranylhydroquinone to an aldehyde moiety concomitant with the isomerization at the C2′–C3′ double bond from the Z-form to the E-form. An enzyme oxidizing this substrate was not detected in other plant cell cultures, suggesting that this enzyme is specific to L. erythrorhizon. The reaction product, (E)-3″-oxo-geranylhydroquinone, was further converted to deoxyshikonofuran, another meroterpenoid metabolite produced in L. erythrorhizon cells. Although nonenzymatic cyclization occurred slowly, it was more efficient in the presence of crude enzymes of L. erythrorhizon cells. This activity was detected in both shikonin-producing and nonproducing cells, suggesting that the aldehyde intermediate at the biosynthetic branch point between naphthalene and benzo/hydroquinone ring formation likely constitutes a key common intermediate in the synthesis of shikonin and benzoquinone products, respectively.

Nonalcoholic steatohepatitis (NASH) is associated with hepatocyte injury, excessive oxidative stress, and chronic inflammation in fatty liver, and can progress to more severe liver diseases, such as cirrhosis and hepatocellular carcinoma. However, currently there are no effective therapies for NASH. Marine carotenoid, fucoxanthin (Fx), abundant in brown seaweeds, has variable biological properties, such as anti-cancer, anti-inflammatory, anti-oxidative and anti-obesity. However, the effect of Fx on the development of NASH has not been explored. We investigated the protective effects of Fx in diet-induced NASH model mice fed choline-deficient L-amino acid-defined high fat diet (CDAHFD). Fx administration significantly attenuated liver weight gain and hepatic fat accumulation, resulting in the alleviation of hepatic injury. Furthermore, the Fx-fed mice, not only exhibited reduced hepatic lipid oxidation, but also decreased mRNA expression levels of inflammation and infiltration-related genes compared to that of the CDAHFD-fed mice. Moreover, fucoxanthinol and amarouciaxanthin A, two Fx metabolites exerted anti-inflammatory effects in the liver via inhibiting the chemokine production in hepatocytes. In case of fibrosis, one of the features of advanced NASH, the expression of fibrogenic factors including activated-hepatic stellate cell marker was significantly decreased in the liver of Fx-fed mice. Thus, the present study elucidated that dietary Fx not only inhibited hepatic oxidative stress and inflammation but also prevented early phase of fibrosis in the diet-induced NASH model mice.

In optogenetics, red-shifted channelrhodopsins (ChRs) are eagerly sought. We prepared six kinds of new chromophores with one double bond inserted into the polyene side chain of retinal (A1) or 3,4-didehydroretinal (A2), and examined their binding efficiency with opsins (ReaChR and ChrimsonR). All analogs bound with opsins to afford new ChRs. Among them, A2-10ex (an extra double bond is inserted at the C10-C11 position of A2) showed the greatest red-shift in the absorption spectrum of ChrimsonR, with a maximum absorbance at 654 nm (67 nm red-shifted from that of A1-ChrimsonR). Moreover, a long-wavelength spectral boundary of A2-10ex-ChrimsonR was extended to 756 nm, which reached into the far-red region (710-850 nm).

Apocarotenoids are carotenoid derivatives in which the polyene chain is cleaved via enzymatic or nonenzymatic action. They are found in animal tissues and carotenoid-containing foods. However, limited information on the biological functions of apocarotenoids is available. Here, we prepared apocarotenoids from astaxanthin via chemical oxidation and evaluated their anti-inflammatory action against macrophages and adipocytes. A series of astaxanthin-derived apoastaxanthinals, apo-11-, apo-15-, apo-14'-, apo-12'-, apo-10'-, and apo-8'astaxanthinals, were successfully characterized by chromatography and spectroscopic analysis. The apoastaxanthinals inhibited inflammatory cytokine production and mRNA expression against lipopolysaccharide-stimulated RAW 264.7 macrophages. Apoastaxanthinals suppressed interleukin-6 overexpression in an in vitro model with macrophages and adipocytes in the following cultures: (1) contact coculture of 3T3-L1 adipocytes and RAW264.7 macrophages and (2) 3T3-L1 adipocytes in a RAW264.7-derived conditioned media. These results indicate that the apoastaxanthinals have the potential for regulation of adipose tissue inflammation observed in obesity.

Vertebrates generally have a single type of rod for scotopic vision and multiple types of cones for photopic vision. Noteworthily, nocturnal geckos transmuted ancestral photoreceptor cells into rods containing not rhodopsin but cone pigments, and, subsequently, diurnal geckos retransmuted these rods into cones containing cone pigments. High sensitivity of scotopic vision is underlain by the rod’s low background noise, which originated from a much lower spontaneous activation rate of rhodopsin than of cone pigments. Here, we revealed that nocturnal gecko cone pigments decreased their spontaneous activation rates to mimic rhodopsin, whereas diurnal gecko cone pigments recovered high rates similar to those of typical cone pigments. We also identified amino acid residues responsible for the alterations of the spontaneous activation rates. Therefore, we concluded that the switch between diurnality and nocturnality in geckos required not only morphological transmutation of photoreceptors but also adjustment of the spontaneous activation rates of visual pigments.

Scope Fucoxanthin is converted to fucoxanthinol and amarouciaxanthin A in the mouse body. However, further metabolism such as cleavage products (i.e., apocarotenoids) remains unclear. The fucoxanthin-derived apocarotenoid in vivo is investigated and the anti-inflammatory effect of apocarotenoids with fucoxanthin partial structure such as allenic bond and epoxide residue against activated macrophages and adipocytes in vitro is evaluated. Methods and results LC-MS analysis indicates the presence of paracentrone, a C31 -allenic-apocarotenoid, in white adipose tissue of diabetic/obese KK-Ay and normal C57BL/6J mice fed 0.2% fucoxanthin diet for 1 week. In lipopolysaccharide-activated RAW264.7 macrophages, paracentrone as well as C26 - and C28 -allenic-apocarotenoids suppresses the overexpression of inflammatory factors. Further, apo-10'-fucoxanthinal, a fucoxanthin-derived apocarotenoid which retained epoxide residue, exhibits a most potent anti-inflammatory activity through regulating mitogen-activated protein kinases and nuclear factor-κB inflammatory signal pathways. In contrast, β-apo-8'-carotenal without allenic bond and epoxide residue lacks suppressed inflammation. In 3T3-L1 adipocytes, paracentrone, and apo-10'-fucoxanthinal downregulate the mRNA expression of proinflammatory mediators and chemokines induced by co-culture with RAW264.7 cells. Conclusion Dietary fucoxanthin accumulates as paracentrone as well as fucoxanthinol and amarouciaxanthin A in the mouse body. Allenic bond and epoxide residue of fucoxanthin-derived apocarotenoids have pivotal roles for anti-inflammatory action against activated macrophages and adipocytes.

As optogenetic studies become more popular, the demand for red-shifted channelrhodopsin is increasing, because blue-green light is highly scattered or absorbed by animal tissues. In this study, we developed a red-shifted channelrhodopsin by elongating the conjugated double-bond system of the native chromophore, all -trans-retinal (ATR1). Analogues of ATR1 and ATR2 (3,4-didehydro-retinal) in which an extra C═C bond is inserted at different positions (C6-C7, C10-C11, and C14-C15) were synthesized and introduced into a widely used channelrhodopsin variant, C1C2 (a chimeric protein of channelrhodopsin-1 and channelrhodopsin-2 from Chlamydomonas reinhardtii). C1C2 bearing these retinal analogues as chromophores showed broadened absorption spectra toward the long-wavelength side and photocycle intermediates similar to the conducting state of channelrhodopsin. However, the position of methyl groups on the retinal polyene chain influenced the yield of the pigment, absorption maximum, and photocycle pattern to a variable degree. The lack of a methyl group at position C9 of the analogues considerably decreased the yield of the pigment, whereas a methyl group at position C15 exhibited a large red-shift in the absorption spectra of the C1C2 analogue. Expansion of the chromophore binding pocket by mutation of aromatic residue Phe265 to Ala improved the yield of the pigment bearing elongated ATR1 analogues without a great alteration of the photocycle kinetics of C1C2. Our results show that elongation of the conjugated double-bond system of retinal is a promising strategy for improving the ability of channelrhodopsin to absorb long-wavelength light passing through the biological optical window.

The total synthesis of myxol stereoisomers 1a,b and deoxymyxol (plectaniaxanthin) stereoisomers 2a,b was accomplished by Wittig reaction of (S)- and (R)-C10-phosphonium salts 8a,b bearing a silyl-protected 1,2-dihydroxy-ψ end group with C30-apocarotenals 6 and 7. The phosphonium salts 8a,b were derived from aldehydes 11a,b possessing a cyclopentylidene ketal moiety, prepared via Sharpless asymmetric epoxidation of allylic alcohol 12 followed by regioselective cleavage of the oxirane ring. We established an analytical HPLC method using a chiral column to separate stereoisomers 1a,b and 2a,b and thus determined the absolute configurations of the natural products. The HPLC analyses established that both myxol and deoxymyxol isolated from bacteria have the 2′S-configuration.

Lycopene-5,6-diol stereoisomers (1a,b) and (2a,b) and γ-carotene-5′,6′-diol stereoisomers (3a,b) and (4a,b) were synthesized by a stepwise C15 + C10 + C15 double Wittig reaction strategy. The key compounds erythro(anti)-C15-dihydroxy aldehydes 17a,b and their threo(syn)-stereoisomers 23a,b were prepared via Sharpless asymmetric epoxidation of geraniol and nerol followed by acidic hydrolysis of the epoxides in a stereospecific manner. The enantiomerically enriched anti-isomers were obtained by way of recrystallization of 2,3-epoxygeranyl 3,5-dinitrobenzoates 9a,b, whereas syn-isomers were obtained as enantiomerically pure forms via recrystallization of dihydroxyneryl 3,5-dinitrobenzoates 21a,b. In order to determine the absolute stereochemistry of natural products, HPLC separation methods for each enantiomers 1a,b–4a,b were established by using a column carrying a chiral stationary phase.

A mild deacylation method for 3,5-dinitrobenzoates using methanolic solutions of amines, such as dialkylamines, was developed. The method's versatility was confirmed by applying it to synthesizing a key intermediate for Colorado potato beetle pheromone.

Carotenoids are natural pigments that contribute to light harvesting and photo-protection in photosynthetic organisms. In this study, we analyzed the carotenoid profiles, including mono-hydroxy and epoxy-carotenoids, in the economically valuable red seaweed Pyropia yezoensis, to clarify the detailed biosynthetic and metabolic pathways in the order Bangiales. P. yezoensis contained lutein, zeaxanthin, &alpha, carotene, and &beta, carotene, as major carotenoids in both the thallus and conchocelis stages. Monohydroxy intermediate carotenoids for the synthesis of lutein with an &epsilon, ring from &alpha, carotene, &alpha, cryptoxanthin (&beta, &epsilon, caroten-3&rsquo, ol), and zeinoxanthin (&beta, caroten-3-ol) were identified. In addition, &beta, cryptoxanthin, an intermediate in zeaxanthin synthesis from &beta, carotene, was also detected. We also identified lutein-5,6-epoxide and antheraxanthin, which are metabolic products of epoxy conversion from lutein and zeaxanthin, respectively, by LC-MS and 1H-NMR. This is the first report of monohydroxy-carotenoids with an &epsilon, ring and 5,6-epoxy-carotenoids in Bangiales. These results provide new insights into the biosynthetic and metabolic pathways of carotenoids in red seaweeds.

Pinopsin is the opsin most closely related to vertebrate visual pigments on the phylogenetic tree. This opsin has been discovered among many vertebrates, except mammals and teleosts, and was thought to exclusively function in their brain for extraocular photoreception. Here, we show the possibility that pinopsin also contributes to scotopic vision in some vertebrate species. Pinopsin is distributed in the retina of non-teleost fishes and frogs, especially in their rod photoreceptor cells, in addition to their brain. Moreover, the retinal chromophore of pinopsin exhibits a thermal isomerization rate considerably lower than those of cone visual pigments, but comparable to that of rhodopsin. Therefore, pinopsin can function as a rhodopsin-like visual pigment in the retinas of these lower vertebrates. Since pinopsin diversified before the branching of rhodopsin on the phylogenetic tree, two-step adaptation to scotopic vision would have occurred through the independent acquisition of pinopsin and rhodopsin by the vertebrate lineage., Sato et al. show that pinopsin, an extraocular opsin, is also expressed in a subpopulation of retinal photoreceptor cells in lower vertebrates. Its retinal expression coupled to its low thermal isomerization rate suggests that pinopsin can function as a visual pigment and provides some insights into the evolution of scotopic vision in vertebrates.

Three new oxidative metabolites of lycopenes, (erythro)-lycopene-5,6-diol, (threo)-lycopene-5,6-diol, and 1,16-dehydro-2,6-cyclolycopene-5-ol B, and four new oxidative metabolites of γ-carotenes, 2',6'-cyclo-γ-carotene-1',5'-diol A, 2',6'-cyclo-γ-carotene-1',5'-diol B, (erythro)-γ-carotene-5,6-diol, and (threo)-γ-carotene-5,6-diol, were isolated as minor components from the aril of gac, Momordica cochinchinensis. These structures were determined on the basis of spectroscopic data, and some of them were compared to the structures of synthetic samples. Furthermore, the oxidative metabolic conversion pathways of lycopene and γ-carotene were discussed.

Most vertebrate retinas contain a single type of rod for scotopic vision and multiple types of cones for photopic and color vision. The retinas of certain amphibian species uniquely contain two types of rods: red rods, which express rhodopsin, and green rods, which express a blue-sensitive cone pigment (M1/SWS2 group). Spontaneous activation of rhodopsin induced by thermal isomerization of the retinal chromophore has been suggested to contribute to the rod’s background noise, which limits the visual threshold for scotopic vision. Therefore, rhodopsin must exhibit low thermal isomerization rate compared with cone visual pigments to adapt to scotopic condition. In this study, we determined whether amphibian blue-sensitive cone pigments in green rods exhibit low thermal isomerization rates to act as rhodopsin-like pigments for scotopic vision. Anura blue-sensitive cone pigments exhibit low thermal isomerization rates similar to rhodopsin, whereas Urodela pigments exhibit high rates like other vertebrate cone pigments present in cones. Furthermore, by mutational analysis, we identified a key amino acid residue, Thr47, that is responsible for the low thermal isomerization rates of Anura blue-sensitive cone pigments. These results strongly suggest that, through this mutation, anurans acquired special blue-sensitive cone pigments in their green rods, which could form the molecular basis for scotopic color vision with normal red rods containing green-sensitive rhodopsin.

In order to determine the absolute configuration of naturally occurring alloxanthin, a HPLC analytical method for three stereoisomers 1a–c was established by using a chiral column. Two authentic samples, (3S,3′S)- and meso-stereoisomers 1b and 1c, were chemically synthesized according to the method previously developed for (3R,3′R)-alloxanthin (1a). Application of this method to various alloxanthin specimens of aquatic animals demonstrated that those isolated from shellfishes, tunicates, and crucian carp are identical with (3R,3′R)-stereoisomer 1a, and unexpectedly those from lake shrimp, catfish, biwa goby, and biwa trout are mixtures of three stereoisomers of 1a–c.

N-Acylethanolamines (NAEs) including N-arachidonoylethanolamine (anandamide) and N-palmitoylethanolamine are endogenous lipid mediators. These molecules are degraded to the corresponding fatty acids and ethanolamine by fatty acid amide hydrolase (FAAH) or NAE-hydrolyzing acid amidase (NAAA). Lipophilic amines, especially pentadecylamine (2c) and tridecyl 2-aminoacetate (11b), were found to exhibit potent NAAA inhibitory activities (IC(50)=5.7 and 11.8μM), with much weaker effects on FAAH. These simple structures would provide a scaffold for further improvement in NAAA inhibitory activity.

The synthesis of 3′-deoxycapsanthin (1) and 3,4-didehydroxy-3′-deoxycapsanthin (2), carotenoids of paprika, has been achieved by employing Lewis acid-promoted regio- and stereoselective rearrangement of the C15-epoxy dienal 5a. The absolute stereochemistry of the newly formed C-5 chiral center of rearrangement product 6a was determined to be (R) from its alternative synthesis derived from (+)-(R)-camphonanic acid (11).

Carotenoid synthesis during the past approximately 30 years is summarized. Total syntheses of peridinin, fucoxanthin and halocynthiaxanthin, and biomimetic total syntheses of mytiloxanthin, crassostreaxanthin B, capsanthin, capsorubin, cucurbitaxanthin A, cycloviolaxanthin and capsanthin 3,6-epoxide are discussed.

We investigated the membrane-stabilizing effect of three synthesized polar carotenoids, thermozeaxanthin (TZ), zeaxanthin glucoside (ZG) and zeaxanthin (Z), using the fluorescent calcein-leakage measurement from the calcein-entrapped liposomes composed of dipalmitoylphosphatidylcholine (DPPC). The addition of TZ stabilized the liposomal membranes composed of DPPC at pH values ranging from 4.0 to 10.0. The addition of three carotenoids, TZ, ZG and Z, stabilized the membrane at acidic and neutral pH values ranging from 4.0 to 7.5. The values of leakage were lower at 30 °C and highest at 40 °C, and subsequently, gradually decreased at the higher temperature. The addition of TZ and Z stabilized the membranes, whereas, ZG destabilized the membranes at a temperature higher than 50 °C. In addition, the membrane-stabilizing effect of the carotenoids with the calcein-entrapped liposomes composed of lipids extracted from Thermus thermophilus were investigated. The addition of TZ resulted in stabilization of the membrane at all ranges of pH values. However, the addition of Z and ZG destabilized the membrane.

Upon-excitation, with subpicosecond pulses, to the pair of overlapped optically-allowed 1 B u + (1) and optically-forbidden 3 A g - (2) levels (‘diabatic levels’), we observed stimulated-emission from five diabatic levels, above and below the original pair, which included 1 B u - (1), 3 A g - (0), 3 A g - (1), 3 A g - (2) and 3 A g - (3). We ascribed this to diabatic excitation followed by radiative transitions between the 3 A g - and 1 B u + (or 1 B u - ) vibronic levels in aggregates. The number of observed stimulated-emission peaks increased from two to five in n -hexane on going from all- trans - to 15- cis -β-carotene, and in all- trans -β-carotene from non-polar to polar solvent, which we ascribed to configurational change and electronic polarization in the conjugated chain.

Low dark noise is a prerequisite for rod cells, which mediate our dim-light vision. The low dark noise is achieved by the extremely stable character of the rod visual pigment, rhodopsin, which evolved from less stable cone visual pigments. We have developed a biochemical method to quickly evaluate the thermal activation rate of visual pigments. Using an isomerization locked chromophore, we confirmed that thermal isomerization of the chromophore is the sole cause of thermal activation. Interestingly, we revealed an unexpected correlation between the thermal stability of the dark state and that of the active intermediate MetaII. Furthermore, we assessed key residues in rhodopsin and cone visual pigments by mutation analysis and identified two critical residues (E122 and I189) in the retinal binding pocket which account for the extremely low thermal activation rate of rhodopsin.

Titania-based Gratzel-type solar cells were fabricated by the use of polyene dyes with various transition dipole moments. In the dye having the largest transition dipole among the samples, an aggregate was readily formed through dispersive interaction, and the photocurrent was increased when the dye concentration or the light intensity was lowered. This observation was ascribed to the suppression of the singlet–triplet annihilation reaction. In the dye having the smallest transition dipole, there was no sign of aggregate formation, and the photocurrent was decreased when the dye concentration or the light intensity was lowered.

Retinoidal γ-hydroxybutenolides 2a–d having various lengths of conjugated double bond were prepared in three steps from the corresponding aldehyde 4. Their biological activities were then measured. Of these compounds, only compound 2c possessing a structure similar to that of retinoic acid showed differentiation-inducing activity and very strong apoptosis-inducing activity in HL-60 cells.

Titanium oxide-based dye-sensitized solar cells (DSSC) were fabricated by the use of retinoic acid and carotenoic acids having the number of conjugated double bonds, n = 5–13. The incident photon-to-current conversion efficiency, the photocurrent density and the solar energy-to-electricity conversion efficiency exhibited the highest values at n = 7, and then decreased toward both sides. The effects of dilution of CA7 with deoxycholic acid were also examined. The above parameters per unit CA7 concentration progressively increased toward the lowest concentration, which is ascribed to the isolated excitation free from singlet–triplet annihilation in the dye molecules on the TiO 2 layer.

A stereocontrolled synthesis of optically active beta-D-glucopyronosides 6a, b and 11a, b was accomplished via the 7,8-saturated alcohols 4a, b, efficiently prepared by an asymmetric transfer hydrogenation of the alpha,beta-acetylenic ketone 1 and subsequent catalytic hydrogenation. Simultaneous separation of these four glucosides by HPLC was also performed. This work is useful not only in order to confirm the stereochemistries of the trace amount of glucosides in plants but also to clarify their biosynthesis.

Thermozeaxanthin and thermocryptoxanthin are efficiently synthesized via β-selective glucosidation of (3R)-3-hydroxy-β-ionone 7, and the stabilizing effects of zeaxanthin 5, its glucoside 3 and thermozeaxanthin-15 1a on liposomes are also examined.

Biomimetic synthesis of mytiloxanthin 1 was accomplished with stereoselective rearrangement of the tetrasubstituted epoxide 5 as a key reaction. This is the first total synthesis of optically active all-E mytiloxanthin 1.

The progenitors of damascenone (1), the most intensive C13-norisoprenoid volatile aroma constituent of rose essential oil, were surveyed in the flowers of Rosa damascena Mill. Besides 9-O-β-D-glucopyranosyl-3-hydroxy-7,8-didehydro-β-ionol (4b), a stable progenitor already isolated from the residual water after steam distillation of flowers of R. damascena Mill., two labile progenitors were identified to be (3S, 9R)- and (3S, 9S)-megastigma-6,7-dien-3,5,9-triol 9-O-β-D-glucopyranosides (2b) based on their synthesis and HPLC-MS analytical data. Compound 2b gave damascenone (1), 3-hydroxy-β-damascone (3) and 4b upon heating under acidic conditions.

(3R)-Gobiusxanthin stereoisomers (1a–d) were synthesized by stereoselective Wittig reaction of the (3R)-C15-acetylenic tri-n-butylphosphonium salt 7 with C25-apocarotenal stereoisomers 5a,b and 14a,b bearing four kinds of 3,6-dihydroxy-ε-end groups. The validity of the reported stereochemistry of gobiusxanthin was demonstrated by the fact that the reported spectral data of natural gobiusxanthin were in agreement with those of synthetic (3R,3'S,6'R)-gobiusxanthin (1a). On the other hand, the reported CD spectral data of natural epigobiusxanthin, which has been assigned as (3R,3'R,6'R)-isomer (3'-epigobiusxanthin), were identical with those of synthetic (3R,3'S,6'S)-isomer 1d (6'-epigobiusxanthin) rather than those of the corresponding synthetic 3'-epi-isomer 1b. It was found that the stereochemistry at C3-position has little effect on the shape of their CD spectra. Thus, in order to reinforce the validity of the absolute configurations at C3-position of natural specimens, (3S,3'S,6'R)- and (3S,3'S,6'S)-stereoisomers 1e and 1f were also synthesized and a HPLC analytical method for four stereoisomers was established by using a column carrying a chiral stationary phase. The HPLC analysis has proven that the stereochemistry of the natural epigobiusxanthin is 3R,3'S,6'S.

Astaxanthin analogues having various lengths of polyene chains are stereoselectively synthesized and their singlet-oxygen-quenching activities are examined.

An isolation of 9Z β-carotene from Dunaliella bardawil was accomplished by low-pressure column chromatography with Ca(OH)2 column. Furthermore, it was stereoselectively synthesized by Wittig re-action between the C10-phosphonium salt 2 and 9Z β-apo-8'-carotenal 1, which was prepared by Emmons-Horner reaction of 9Z β-ionylidene-acetaldehyde 3 with phosphonates 6 and 7 or 8a and 9.

The novel acyclic tetrasubstituted olefinic end group and the cyclopentyl end group of carotenoids were obtained by Lewis acid-promoted stereoselective rearrangement of the epoxide end group of 5,6-epoxy carotenoids. The scope and limitation of this rearrangement were investigated.

An analogue of retinal ( β -apo-12′-carotenal), its terminal-methyl group being shifted from the 13 to 14 (from 13′ to 14′) position, was subjected to direct (iodine-sensitized) photo-isomerization. The configurations of five (seven) isomers of the retinal ( β -apo-12′-carotenal) analogue were determined by 1 H-NMR spectroscopy to be all- trans , 7-, 9- and 11-mono- cis and 9,11-di- cis (all- trans , 9-, 13- and 13′-mono- cis and 9,13-, 9,13′- and 13,13′-di- cis ). Comparative direct photo-isomerization in acetonitrile of the above parent and analogue aldehydes showed that the kinds and the amounts of cis isomer produced in the stationary-state mixtures are drastically affected by the terminal-methyl position and by the length of the conjugated chain. The results are discussed in terms of enhanced polarization upon excitation in the terminal CO and the neighbouring CC bonds in the conjugated chain.

An analogue of all- trans -β-apo-12′-carotenal, with a methyl group being shifted from the 13′ to the 14′ position, has been synthesized. The electronic absorption, the 1 H and 13 C NMR, and the S 0 -, S 1 - and T 1 -state Raman spectra of β-apo-12′-carotenal (C 25 aldehyde) and the analogue (C 25′ aldehyde) were recorded for comparison. No clear differences were found for the A g → B u absorption, but systematic differences were found in the 13 C and 1 H chemical shifts in the vicinity of the methyl group; the differences were explained in terms of the inductive effect and van der Waals interactions. The frequency of the in-phase CC stretching Raman line (a measure of the overall carbon-carbon bond order of the conjugated chain) was almost the same in the S 0 state, but the CC stretching frequency of C 25′ aldehyde was lower than that of C 25 aldehyde in both the S 1 and T 1 states. Thus, the methyl position affects only the local electronic structure in the So state, but it can affect the electronic structure of the entire conjugated backbone in the excited states.