- Triene Photophysics and Photochemistry: Previtamin D3
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The origin of the wavelenght dependent photochemical behavior of previtamin D3 was investigated.The fluorescence spectrum and quantum yield of previtamin D3 were determined at 302 and 307 nm, and both the intensity distribution and the fluorescence quantum yields were found to be independent of excitation energy.A large Stokes shift was observed which is consistent with an excited state torsional relaxation about the central double bond of the triene.The excited state displacement was reproduced by QCFF/PI calculations of the ground and excited states of a model compound.The excited state involved in the absorption and emission spectra is discussed.
- Dauben, William G.,Share, Paul E.,Ollmann, Richard R., Jr.
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- Biomimetic Synthesis of Chaxine and its Related Compounds
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The highly oxidized natural products chaxine B and BB have been synthesized from ergosterol in eight steps according to a route inspired by their proposed biosynthesis; key steps were an oxidative cascade from a furan intermediate to an enol ester using m-chloroperbenzoic acids (MCPBA), followed by diastereoselective epoxidation and acyloxy migration. This concise synthesis resulted in the revision of the structures of chaxine B and its naturally occurring analogs and syntheses of the unnatural analogues of these natural products for biological investigations.
- Niki, Misaki,Hirata, Yushi,Nakazaki, Atsuo,Wu, Jing,Kawagishi, Hirokazu,Nishikawa, Toshio
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p. 4848 - 4860
(2020/05/08)
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- Photo-conversion of two epimers (20R and 20S) of pregna-5,7-diene-3β, 17α, 20-triol and their bioactivity in melanoma cells
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Pregna-5,7-dienes and their hydroxylated derivatives can be formed in vivo when there is a deficiency in 7-dehydrocholesterol (7-DHC) Δ-reductase function, e.g., Smith-Lemli-Opitz syndrome (SLOS). Ultraviolet B (UVB) radiation induces photoconversion of 7-DHC to vitamin D3, lumisterol3 and tachysterol3. Two epimers (20R and 20S) of pregna-5,7-diene-3β,17α,20-triol (4R and 4S, respectively) were synthesized and their UVB photo-conversion products identified as corresponding 9,10-secosteroids with vitamin D-like and tachysterol-like structures, and 5,7-dienes with inverted configuration at C-9 and C-10 (lumisterol-like). The number and character of the products and the dynamics of the process were dependent on the UVB dose. At high UVB doses, the formation of multiple oxidized derivatives of the primary products, and the formation of 5,7,9(11)-triene, were observed. The production of vitamin D-like, tachysterol-like and lumisterol-like derivatives was also observed in human skin treated with 4R and 4S, and subjected to UV irradiation, as shown by RP-HPLC. Newly synthesized compounds inhibited melanoma growth in dose dependent manner, and some of them showed equal or higher potency than 1,25(OH)2D3. In summary, we have characterized for the first time the products of UV induced conversion of pregna-5,7-diene-3β,17α,20-triols and documented that the newly synthesized compounds have antiproliferative properties against melanoma cells.
- Zmijewski, Michal A.,Li, Wei,Zjawiony, Jordan K.,Sweatman, Trevor W.,Chen, Jianjun,Miller, Duane D.,Slominski, Andrzej T.
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scheme or table
p. 218 - 228
(2009/04/14)
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- Effects of surface adsorption and confinement on the photochemical selectivity of previtamin D3 adsorbed within porous sol-gel derived alumina
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It has been demonstrated that porous sol-gel derived (SGD) alumina can function as an effective microorganized medium in which to perform size- or shape-selective organic transformations. For the photolysis of 7- dehydrocholesterol (7D) encapsulated within SGD-alumina, it was found that the adsorption characteristics of 7D and the pore size of the SGD-alumina greatly influenced the photochemical selectivity of the cis-trans isomerization of previtamin D3 to tachysterol3. An increase in the ratio of previtamin D3 (P3) to tachysterol3 (T3) was obtained on photolysis of 7D adsorbed within SGD-alumina with a pore size of 10-20 ?. This result is attributed to a confinement effect that inhibits the cis-trans isomerization of P3 to T3. In addition to the confinement effect on the photochemical selectivity, it was found that the adsorption characteristics of 7D to the surface of SGD-alumina also play a critical role in the photochemical selectivity. The results indicate that confinement in addition to chemisorption via the 3-hydroxyl group of 7D to the surface of activated SGD- alumina is necessary to optimize the photochemical selectivity. The presented results also provide direct experimental evidence to demonstrate that adsorption solely to a metal oxide surface via the 3-hydroxyl group is not sufficient to inhibit the cis-trans isomerization of P3 to D3.
- Schultz, Forrest S.,Anderson, Marc A.
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p. 4933 - 4940
(2007/10/03)
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- Novel Photosensitizers for the E/Z-Isomerization of Trienes. Part 1. Synthesis and Application
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Uranine and its thioxanthene and selenoxanthene analogues, as well as the disodium salts of o-(6-hydroxy-3-oxo-3H-xanthen-9-yl)benzenesulphonic acid and its thioxanthene and selenoxanthene analogues, show different photosensitizer properties in the E/Z-isomerization of trienes.This has been verified by applying them to the technically useful conversion of tachysterol into previtamin D.The synthesis of the novel photosensitizers with thioxanthene and selenoxanthene moieties are also described.
- Pfoertner, Karl-Heinz
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p. 523 - 526
(2007/10/02)
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- ORGANIC REACTIONS AT HIGH PRESSURE. INTERCONVERSION OF PREVITAMIN D3 AND VITAMIN D3.
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The interconversion of previtamin D3 and vitamin D3 at 20 deg C was effected at high pressure (15 kbar) in three solvent mixtures.The rate constants of k1 and k2 were determined to be 30 to 45 times larger than the corresponding 1 bar rate constants.The ΔV* was calculated to be -5.14 cm3/mol or lower, indicating a concerted sigmatropic hydrogen shift.
- Dauben, William G.,Kowalczyk, Bruce A.,Funhoff, Dirk J. H.
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p. 3021 - 3024
(2007/10/02)
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- Determination of the Molar Absorptivity (ε) of the Photoisomers of 3β-Hydroxy-cholest-5,7-diene (Provitamin D3)
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A method is described which allows the determination of the molecular absorptivity (ε) of all components in a four-component system and is applied to the ε-determination of the photoisomers of provitamin D3 (1): praevitamin D3 (2), lumisterol3 (3), and tachysterol3 (4).By means of irradiation with appropriate wavelengths the four-component system is reduced to a two- and a three-component system, respectively, and the unknown molar absorptivities are evaluated numerically or graphically.
- Gliesing, S.,Reichenbaecher, M.,Ilge, H.-D.,Fassler, D.
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p. 311 - 320
(2007/10/02)
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- Calciferol and its Relatives. Part 27. A Synthesis of 1α-Hydroxyvitamin D3 by way of 1α-Hydroxytachysterol3
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A new synthesis of 1α-hydroxyvitamin D3 is described.The bis-t-butyldimethylsilyl ether (17) of (3S,5R)-3,5-dihydroxy-2-methylcyclohex-1-enecarbaldehyde and 8-p-tolylsulphonylmethyl-des-AB-cholest-8-ene (4) were combined to give mixed benzoyloxysulphones which, on reductive elimination with sodium amalgam, gave the corresponding bis-ether of 1α-hydroxytachysterol3.This was isomerised photochemically to the bis-ether of 1α-hydroxyprecalciferol3, and then thermally to give the bis-ether of 1α-hydroxyvitamin D3.Removal of protecting groups gave 1α-hydroxyvitamin D3 (21) in 62percent yield from the sulphone (4), or 12.8percent overall from cholesterol.
- Kocienski, Philip J.,Lythgoe, Basil
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p. 1400 - 1404
(2007/10/02)
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