- Artificial photosynthetic reaction centers with carotenoid antennas
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Two reaction center-antenna models based on a purpurin macrocycle linked to a C60 and to a carotenoid polyene have been synthesized. In these systems the C60 moiety is the primary electron acceptor, the purpurin is the primary electr
- Gould, Stephanie L.,Kodis, Gerdenis,Liddell, Paul A.,Palacios, Rodrigo E.,Brune, Alicia,Gust, Devens,Moore, Thomas A.,Moore, Ana L.
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p. 2074 - 2096
(2007/10/03)
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- Effect of meso-substituents on the osmium tetraoxide reaction and pinacol-pinacolone rearrangement of the corresponding vic-dihydroxyporphyrins
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To investigate the effects of electron-donating and electron-withdrawing substituents upon the reaction of porphyrins with osmium tetraoxide, and the pinacol-pinacolone rearrangement of the resulting diols, a series of meso-substituted porphyrins were prepared by total synthesis. Porphyrins with electron-donating substitutents at the meso-positions gave vic-dihydroxychlorins in which the adjacent pyrrole subunit was predominantly oxidized. No such selectivity was observed in a porphyrin containing a methoxycarbonyl as the electron-withdrawing group, whereas a formyl substituent again resulted in oxidation at the pyrrole unit adjacent to the meso-substituent. Under pinacol-pinacolone conditions, vic-dihydroxy chlorins containing 4-methoxyphenyl or 3,5-dimethoxyphenyl groups at the meso-position showed preferential migration of the ethyl group over the methyl group to give 8-ketochlorins, whereas the diol with an n-heptyl substituent under similar reaction conditions gave both 7- and 8-ketochlorins. In contrast, the diol containing a meso-formyl substituent produced the corresponding 7-ketochlorin exclusively. These results indicate that it is not possible to predict the reactivity of meso-substituted porphyrins in the osmium tetraoxide reaction nor the general substituent migratory aptitudes in the pinacol-pinacolone rearrangement based on simple electronic arguments, most likely because many parameters (e.g., meso-β-pyrrolic steric crowding and long-range electronic effects) ultimately determine the reactivity. The structural assignments of the porphyrin diols and the keto-analogues were confirmed by extensive 1H NMR studies; some of the dihydroxychlorins and ketochlorins were found to display unusual features in their 1H NMR spectra.
- Chen,Medforth,Smith,Alderfer,Dougherty,Pandey
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p. 3930 - 3939
(2007/10/03)
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- Porphyrins with exocyclic rings. Part 12. Synthesis of meso,β-butano- and meso,β-pentanoporphyrins from cycloalka[b]pyrroles
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Pyrroles 5 with b-face fused seven- or eight-membered carbocyclic rings were prepared in good yields by Knorr-type condensations with cycloheptanone or cyclooctanone, respectively. Treatment with lead tetraacetate in dichloromethane afforded the labile ω-acetates 8 and subsequent acid catalyzed condensation with α-unsubstituted pyrrole-2-carboxylates yielded the related pyrrolylcycloalka[b]pyrroles 29 and 30. The α-unsubstituted pyrroles 14 and 23 were prepared by condensing α,β-unsubstituted ketones, or their β-acetoxycarbonyl precursors, with benzyl N-tosylglycinate in the presence of DBU, followed by dehydration with POCl3-pyridine and base catalyzed elimination of p-toluenesulfinic acid. Dipyrrole dibenzyl esters 29 and 30 were hydrogenolysed over 10% Pd-C to give the corresponding dicarboxylic acids. Acid catalyzed condensation with diformyldipyrrylmethane 33 under modified MacDonald '2 + 2' conditions afforded a series of four cycloalkanoporphyrins 4a-d with seven- or eight-membered exocyclic rings. Although the meso,β-butanoporphyrins 4a and 4b were isolated in good yields, poorer results were obtained for the related meso,β-pentanoporphyrin: 4c and 4d. It is proposed that the eight-membered carbocyclic ring distorts the geometry of the open-chain tetrapyrrolic intermediates and this deleterious influence results in the lower yields observed.
- Bastian, Jolie A.,Lash, Timothy D.
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p. 6299 - 6310
(2007/10/03)
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- A new convergent method for porphyrin synthesis based on a '3 + 1' condensation
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A new methodology based on the '3 + 1' acid-catalytic condensation of tripyrranes and pyrrole-2,5-dicarbaldehyde has been used, for the first time, for the synthesis of two types of porphyrins: vic-dipropionic ester porphyrins 30 and 31 including an analo
- Boudif, Arezki,Momenteau, Michel
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p. 1235 - 1242
(2007/10/03)
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- Regioselective synthesis of 5-unsubstituted benzyl pyrrole-2-carboxylates from benzyl isocyanoacetate
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A general synthesis of 5-unsubstituted benzyl pyrrole-2-carboxylates was developed based on the reaction of β-nitroacetates with benzyl isocyanoacetate. The advantage of this route over other pyrrole syntheses was the regiochemical control of the substitution pattern on the pyrrole ring.
- Ono,Katayama,Nisyiyama,Ogawa
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p. 707 - 710
(2007/10/02)
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- Synthesis of pyrroles from benzyl isocyanoacetate
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Benzyl esters of 5-unsubstituted pyrrole-2-carboxylic acids were prepared in excellent yields by the base-catalyzed condensation of benzyl isocyanoacetate with α-acetoxynitro compounds, or nitro-alkenes, in refluxing tetrahydrofuran. These pyrrolic products are important intermediates in the synthesis of porphyrins and related compounds.
- Lash,Bellettini,Bastian,Couch
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p. 170 - 172
(2007/10/02)
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- Porphyrins with Exocyclic Rings. Part 3. A Reassessment on the Utility of Cyclopentapyrroles in the Synthesis of Porphyrin Molecular Fossils. Preparation of Three Type II Porphyrins Related to Deoxophylloerythroetioporphyrin (DPEP)
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The utility of cyclopentapyrroles in porphyrin synthesis has been reinvestigated.A 6-oxocyclopentapyrrole 18 was prepared by cyclization of the propanoyl chloride sidechain of an α-unsubstituted pyrrole 17d in the presence of tin(IV) chloride.Subsequent reduction with sodium borohydride afforded the corresponding 6-hydroxy compound 10 and further acid catalyzed condensation with α-unsubstituted pyrroles 11a and 11b gave the novel 6-pyrrolylcyclopentapyrroles 22a and 22b in excellent yields.Attempts to prepare deoxophylloerythroetioporphyrin (DPEP; 2), a widespread sedimentary porphyrin molecular fossil, from these dipyrrolic intermediates using the tripyrrene-a,c-biladiene route were unsuccessful.However, the synthesis of three related meso,β-ethanoporphyrins using the MacDonald condensation was successfully carried out in moderate to good yields.Retention of an sp3 hybridized carbon bridge at the cyclopentene ring fusion site of the intermediary open chain tetrapyrroles appears to be crucial during macrocycle formation, as this diminishes the steric repulsion between the peripheral substituents and the carbocyclic ring.
- Lash, Timothy D.,Catarello, James J.
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p. 4159 - 4172
(2007/10/02)
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- THE TOTAL SYNTHESIS OF BILIVERDINS OF BIOLOGICAL INTEREST
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The total synthesis of eight biliverdin isomers was achieved by oxidation of the corresponding 1,19-di-t-butyloxycarbonyl-b-bilenes.One of the biliverdin isomers is mesobiliverdin IXα - a dipropionate bilitriene -, one is a diacetate bilitriene, three iso
- Awruch, Josefina,Frydman, Benjamin
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p. 4137 - 4146
(2007/10/02)
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- Novel Porphyrins from Copper(II)-Mediated Cyclizations of 1',8'-Dimethyl-a,c-biladiene Salts: Mechanism of the Cyclization Reaction
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Copper(II)-mediated cyclizations of the 1',8'-dimethyl-a,c-biladiene 8 under various conditions afford the expected porphyrin 7, along with γ-methyl- (9), γ-(dialkylamino)- (10 and 11), 6-formyl- (12), and γ-formylporphyrins (13).Carbon-13-enriched a,c-bi
- Smith, Kevin M.,Minnetian, Ohannes M.
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p. 2073 - 2080
(2007/10/02)
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- An Improved Approach to 5'-Unsubstituted 5-Formyldipyrromethanes
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A general synthesis of 5'-unsubstituted 5-formylpyrromethanes, precursors to centrosymmetric porphyrins, is described.Cyanovinyl groups are used to protect the aldehydes and stabilize the dipyrromethanes. 5-(Chloromethyl)-2-(2,2-dicyanovinyl)pyrroles were condensed with 5-unsubstituted pyrrole-2-carboxylate ethyl esters in warm glacial acetic acid to give a series of 5'-(ethoxycarbonyl)-5-(2,2-dicyanovinyl)-2,2'-dipyrromethanes in high yield.Aqueous alkali was used to deprotect the dicyanovinyl substituent to regenerate the aldehyde and saponify the ethyl ester in a single step.The acid group was subsequently decarboxylated thermally to give the 5'-unsubstituted 5-formyl-2,2'-dipyrromethane.An alternative route was also designed by substitution of a benzyl for an ethyl ester.Hydrogenolysis released the carboxylic acid without affecting the cyanovinyl group, and the subsequent decarboxylation in neat trifluoroacetic acid accurred without rearrangement.Deprotection using aqueous alkali produced crystalline 5'-unsubstituted 5-formyldipyrromethane.The complete lack of rearrangement during the synthesis and manipulation of the dipyrromethanes was confirmed by 13C NMR spectroscopy.
- Wijesekera, Tilak P.,Paine, John B.,Dolphin, David
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p. 3832 - 3838
(2007/10/02)
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- Synthetic Approaches to Versatile Hemoprotein Model Compounds Built from Porphyrins and Peptides
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Several strategies for the preparation of mono- and bi-functional porphyrins (amino and carboxylate) to which oligopeptides can be attached have been investigated.A porphyrinyl amino-acid derivative has been synthesised by coupling a porphyrin monopropion
- Jackson, Anthony H.,Kenner, George W.,Smith, Kevin M.,Suckling, Colin J.
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p. 1441 - 1448
(2007/10/02)
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