Sunlamp Irradiation Research Articles

Desulfitative Thioalkylation of Alkenes

AbstractAn efficient method for the thioalkylation of alkenes via radical desulfitative sulfur‐group transfer is described. The reaction is based on the use of readily available thiosulfonates as starting materials and cheap radical initiators such as dilauroyl peroxide (DLP) and sun lamp irradiation. No transition metal catalyst is required, and the reaction takes place under mild conditions.magnified image

ChemInform Abstract: A Facile Preparation of Dialkyl Phosphonate Compounds from Sterically Hindered p-Nitrocumyl Halides Through the SRN1 Mechanism.

p-Nitrobenzyl phosphonate anion with p-nitrocumyl halides gives a good yield of the coupling product dialkyl[(1,1-dimethyl-1,2-di-(p-nitrobenzyl)ethyl] phosphonates through the SRN1 mechanism. The reaction was greatly accelerated by sunlamp irradiation but inhibited by the radical scavenger (t-Bu)2NO•.

Et2AlCl‐Promoted Asymmetric Phenylseleno Group Transfer Radical Cyclization Reactions of Unsaturated β‐Hydroxy Esters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Et2AlCl-Promoted Asymmetric Phenylseleno Group Transfer Radical Cyclization Reactions of Unsaturated β-Hydroxy Esters

We have developed a new method for asymmetric phenylseleno group transfer radical cyclization of unsaturated beta-hydroxy esters. Various unsaturated alpha-phenylseleno beta-hydroxy esters underwent radical cyclization in the presence of Et(2)AlCl in benzene with sunlamp irradiation at 25-30 degrees C to give mono- and bicyclic group-transferred products in an efficient and highly regioselective and diastereoselective manner. To rationalize the high diastereoselectivities observed in this reaction, we propose a model based on chelation control of the aluminum alkoxides that are formed in situ. We devised a general method to prepare chiral radical precursors from which we obtained highly optically pure mono- and bicyclic group transfer products. The synthetic advantages of this method are demonstrated by our formal total synthesis of (-)-wilforonide. This paper presents the first examples of stereoselective group transfer radical cyclizations that occur via 1,2-asymmetric induction.

Nitration of Heteroaryltrimethyltins by Tetranitromethane and Dinitrogen Tetroxide: Mechanistic Aspects, Scope and Limitations.

For Abstract see ChemInform Abstract in Full Text.

Nitration of Heteroaryltrimethyltins by Tetranitromethane and Dinitrogen Tetroxide: Mechanistic Aspects, Scope and Limitations

AbstractThe nitration of 2‐(trimethylstannyl)heteroarenes by tetranitromethane (TNM) or dinitrogen tetroxide has been shown to be possible when the HOMO energy of the heteroaryltin is high enough to allow the formation of the corresponding radical cation. The reaction proceeds through a charge‐transfer complex between heteroaryltin and TNM, followed by a single‐electron transfer, which is enhanced under sunlamp irradiation. Accordingly, 2‐nitrobenzo[b]furan, 2‐nitrobenzo[b]thiophene, 2‐nitropyridine and 2‐nitroindoles were obtained by this method. However, the nitration of 2‐stannylated pyrimidine or of stannylated 1,3,5‐triazines has been shown to be impossible, due to the low energy of their HOMO orbitals. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Organotin mediated nitration in heteroaromatic series using tetranitromethane or dinitrogen tetroxide

2-Trimethylstannylated benzo[ b]furan, benzo[ b]thiophene, N-substituted indoles and pyridine afford the corresponding nitro derivatives in regioselective fashion upon treatment with tetranitromethane (using sun-lamp irradiation in the case of N-containing heterocycles) or with dinitrogen tetroxide.

Inhibition of Solar Simulator-Induced p53 Mutations and Protection Against Skin Cancer Development in Mice by Sunscreens

We demonstrated previously that p53 mutations can be detected in ultraviolet B-irradiated mouse skin months before the gross appearance of skin tumors and that applying sun protection factor 15 sunscreens to mouse skin before each Kodacel-filtered FS40 sunlamp irradiation resulted in the reduction of such mutations. To determine whether there is an association between reduction of ultraviolet-induced p53 mutations by sunscreens and protection against skin cancer using an environmentally relevant light source, we applied sunscreens (sun protection factors 15-22) on to the shaved dorsal skin of C3H mice 30 min before each exposure to 4.54 kJ ultraviolet B (290-400 nm) radiation per m2 from a solar simulator. Control mice were treated 5 d per wk with ultraviolet only or vehicle plus ultraviolet. p53 mutation analysis indicated that mice exposed to ultraviolet only or vehicle plus ultraviolet for 16 wk (cumulative exposure to 359 kJ ultraviolet B per m2) developed p53 mutations at a frequency of 56%-69%, respectively, but less than 5% of mice treated with sunscreens plus ultraviolet showed evidence of p53 mutations. More importantly, 100% of mice that received a cumulative dose of 1000 kJ ultraviolet B per m2 only, or vehicle plus ultraviolet B developed skin tumors, whereas, the probability of tumor development in all the mice treated with the sunscreens plus 1000 kJ ultraviolet B per m2 was 2% and mice treated with sunscreens plus 1500 kJ ultraviolet B per m2 was 15%. These results demonstrate that the sunscreens used in this study not only protect mice against ultraviolet-induced p53 mutations, but also against skin cancers induced with solar-simulated ultraviolet. Because of this association, we conclude that inhibition of p53 mutations is a useful early biologic endpoint of photoprotection against an important initiating event in ultraviolet carcinogenesis.

The Photochemical Synthesis of α,α,α-bromodifluorotoluene and α,α,α-chlorodifluorotoluene

The syntheses of α, α, α-chlorodifiuorotoluene and α, α, α-bromodifluorotoluene from α, α-difluorotoluene and N-chlorosuccinimide and N-bromosuccinimide, respectively, were achieved photochemically using sunlight and/or sunlamp irradiation. These methods gave high product yields and very little by-product formation.

A facile preparation of dialkyl phosphonate compounds from sterically hindered p-nitrocumyl halides through the S RN1 mechanism

p-Nitrobenzyl phosphonate anion with p-nitrocumyl halides gives a good yield of the coupling product dialkyl[(1,1-dimethyl-1,2-di-( p-nitrobenzyl)ethyl] phosphonates through the S RN1 mechanism. The reaction was greatly accelerated by sunlamp irradiation but inhibited by the radical scavenger ( t-Bu) 2NO •.

Synthesis, Characterization, and Comparative Properties of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)

The reaction of [PPN](2)[Re(6)C(CO)(19)] with Mo(CO)(6) and Ru(3)(CO)(12) under sunlamp irradiation provided the new mixed-metal clusters [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] and [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)], which were isolated in yields of 85% and 61%, respectively. The compound [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] crystallizes in the monoclinic space group P2(1)/c with a = 20.190 (7) Å, b = 16.489 (7) Å, c = 27.778 (7) Å, beta = 101.48 (2) degrees, and Z = 4 (at T = -75 degrees C). The cluster anion is composed of a Re(6)C octahedral core with a face capped by a Mo(CO)(4) fragment. There are three terminal carbonyl ligands coordinated to each rhenium atom. The four carbonyl ligands on the molybdenum center are essentially terminal, with one pair of carbonyl ligands (C72-O72 and C74-O74) subtending a relatively large angle at molybdenum (C72-Mo-C74 = 147.2(9) degrees ), whereas the remaining pair of carbonyl ligands (C71-O71 and C73-O73) subtend a much smaller angle (C71-Mo-C73 = 100.5(9) degrees ). The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows signals for four sets of carbonyl ligands at -40 degrees C, consistent with the solid state structure, but the carbonyl ligands undergo complete scrambling at ambient temperature. The (13)C NMR spectrum of (13)CO-enriched [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] at 20 degrees C is consistent with the expected structure of an octahedral Re(6)C(CO)(18) core capped by a Ru(CO)(3) fragment. The visible spectrum of [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)] shows a broad, strong band at 670 nm (epsilon = 8100), whereas all of the absorptions of [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)] are at higher energy. An irreversible oxidation wave with E(p) at 0.34 V is observed for [PPN](2)[Re(6)C(CO)(18)Mo(CO)(4)], whereas two quasi-reversible oxidation waves with E(1/2) values of 0.21 and 0.61 V (vs Ag/AgCl) are observed for [PPN](2)[Re(6)C(CO)(18)Ru(CO)(3)]. The molybdenum cap in [Re(6)C(CO)(18)Mo(CO(4))](2-) is cleaved by heating in donor solvents, and by treatment with H(2), to give largely [H(2)Re(6)C(CO)(18)](2-). In contrast, [Re(6)C(CO)(18)Ru(CO)(3)](2-) shows no tendency to react under similar conditions.

Different rates of ultraviolet-induced DNA damage in the epidermis and dermis of a platyfish model for carcinogenesis.

The purpose of this study was to compare fluence-response relationships for the production of cyclobutane pyrimidine dimers in epidermal or dermal DNA of platyfish Xiphophorus hybrids irradiated with UVB, and to determine photoreactivation from black light on dimers produced in situ. This was accomplished by quantitative gel electrophoresis of unlabeled DNA following extraction of the DNA and treatment with an enzyme specific for the detection of pyrimidine dimers. The dermis was the target tissue for UV-induced DNA damage in Xiphophorus hybrid fish skin. Shapes of dimer-fluence response data following filtered sunlamp irradiation (lambda > 290 nm) or monochromatic wavelength 302 nm in the epidermis or dermis were different. In the epidermis there was an initial step upward slope followed by a plateau, whereas in the dermis a linear relationship was observed. The final values of dimers at the high doses were, however, nearly equal in the epidermis and dermis exposed to either radiation. These differences in fluence-response relationships are probably attributable to the intertwining of the epidermis and to the shielding effect of the epidermal layer, with scales leading to a heterogeneous population of cells which are exposed to different UV doses. Photoreversal of dimers was readily observed by black light irradiation in both epidermis and dermis irradiated with either lambda > 290 nm or 302 nm.

Metalation of fullerene (C60) with pentacarbonylrhenium radicals. Reversible formation of C60{Re(CO)5}2

Xenon lamp flash photolysis or continuous sunlamp irradiation of Re 2 (CO) 10 with C 60 in benzene produces a new species with IR (ν CO ) bands at 2134, 2130 (sh), 2036, and 1993 cm -1 . This product is assigned as C 60 {Re(CO) 5 } 2 primarily on the basis of a quantitative IR study of its formation stoichiometry. Similar results are obtained from the thermal reaction of C 60 with a known source of rhenium pentacarbonyl radicals, viz., (η 3 -Ph 3 C)Re(CO) 4 , in the presence of CO

DNA damage, photorepair, and survival in fish and human cells exposed to UV radiation

The effect of various wavelengths of UVB radiation on the induction of cyclobutane pyrimidine dimers in fish cells and human fibroblasts and the repair of these lesions were studied using an UV-endonuclease to measure dimers (endonuclease sensitive sites) by sedimentation of radioactive DNA, by gel electrophoresis of unlabeled DNA, and by cell survival. The data show that fish cells have an efficient photoreactivation system at wavelength > 304 nm that reverses cytotoxicity and dimer formation after exposure to filtered sunlamp irradiation of a shorter wavelength (lambda > 290 nm). Shorter wavelengths in UVB (> 304 nm) are more effective in photoreversal than longer ones (> 320 nm). As a consequence, 50-85% of dimers induced by these wavelengths in fish are photoreactivated while they are being formed. A major cytotoxicological lesion is the cyclobutane pyrimidine dimers. Cultured human fibroblasts do not possess such a repair system. These results indicate that sunlamp irradiation has wavelengths that both damage and repair DNA.

Radical Isomerization and Allylation Reactions of 2-Iodo-3,3-dimethyl-4-pentenoate Esters

Sunlamp irradiation of methyl 2-iodo-3,3-dimethyl-4-pentenoate (2c) induces isomerization to an equilibrium mixture rich (13/1) in methyl 3-iodo-3-methyl-2-vinylbutanoate (3c). Allylations of 2c with allyl sulfides and stannanes produce mixtures of rearranged (9; 6-substituted 3-methoxycarbonyl-4,4-dimethyl-1,6-heptadienes) or unrearranged (8; 6-substituted 4-methoxycarbonyl-3,3-dimethyl-1,6- heptadienes) allylation products.

Effects of temperature on atom transfer cyclization reactions of allylic .alpha.-iodo esters and amides

Atom-transfer cyclizations of allyl iodoacetates and N-alyl-N-methyliodoacetamides are much more efficient at 80°C than at 25°C. At 80°C, β-(iodomethyl) lactones and lactams are formed rapidly and in good yield under standard atom-transfer conditions (sunlamp irradiation of iodide and 10% hexabutylditin in benzene for 10−60 min). It is proposed that this temperature effect is responsible for some unusual observations by Jolly and Livinghouse in the cyclization of N-cyclohexenyl-N-methyliodoacetamide. The results suggest that the beneficial effect of temperature arises because an increase in the rate of rotation of the OC−O or OC−N bond in the intermediate radicals begins to convert syn radicals (which cannot cyclize) to anti radicals (which can cyclize)

4 + 1 Radical annulations with isonitriles: a simple route to cyclopenta-fused quinolines

Sunlamp irradiation of 1-substituted 5-iodo-1-pentynes, 5 equiv of phenyl isocyanide, and 1.5 equiv of hexamethylditin in tert-butylbenzene (0.01-0.025 M) at 150 o C produces 9-substituted 2,3-dihydro-1H-cyclopenta [b] quinolines in 36-70% yields. A mechanistic proposal for this first example of a 4+1 radical annulation includes the following: (1) radical addition to an isonitrile, (2) cyclization of the resulting imidoyl radical to the alkyne, (3) addition of the so-formed vinyl radical to the aromatic ring, and (4) rearomatization. When substituted isonitriles (p-F p-OMe, m-F) are employed, the major unrearranged products are accompanied by 7-30% or rearranged products. Independent generation of a proposed intermediate suggests that the rearranged products arise by initial closure of the vinyl radical to form a five-membered ring, followed by C-N bond cleavage and recyclization

RESEARCH NOTE

Fluorescence microscopy has been utilized to investigate the effects of UV irradiation on the organization of keratin intermediate filaments in normal human epidermal keratinocytes. Sun lamp irradiation induced the condensation of keratin intermediate filaments into the perinuclear region and inhibited the reorganization of keratin filaments normally induced by Ca2+. Exposure to UVC appeared to disrupt keratin filaments similarly, whereas UVA had no discernible effect.

Reproduction of the Skin Lesions of Polymorphous Light Eruption: A Case Report and a Review of the Japanese Literature

A case of polymorphous light eruption with plaque-type lesions is reported. A 55-year-old male had pruritic erythemas and plaques on the head, the face, the nape, the back of the hands, and the left loin within days following sun exposure. The patient's minimal erythema dose (MED) (60 mJ/cm2) of sunlamp irradiation for ultraviolet (UV) B was normal. Three once-daily exposures to 2 MED of UVB (Epstein's repeat phototest technique) produced pruritic papules with a similar microscopic appearance to that of the patient's skin lesion, indicating that the action spectrum causing the lesion seemed to be within the UVB waveband.

Chlorpromazine ingestion inhibits UV-induced skin carcinogenesis.

Abstract Chlorpromazine (0.01% in drinking water) inhibits the induction of skin cancer by sunlamp irradiation of hairless mice. This inhibition is partially reversed by a single injection of ethyl nitrosourea at birth.