RESUMEN
The intergalactic medium was not completely reionized until approximately a billion years after the Big Bang, as revealed by observations of quasars with redshifts of less than 6.5. It has been difficult to probe to higher redshifts, however, because quasars have historically been identified in optical surveys, which are insensitive to sources at redshifts exceeding 6.5. Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang. ULAS J1120+0641 has a luminosity of 6.3 × 10(13)L(â) and hosts a black hole with a mass of 2 × 10(9)M(â) (where L(â) and M(â) are the luminosity and mass of the Sun). The measured radius of the ionized near zone around ULAS J1120+0641 is 1.9 megaparsecs, a factor of three smaller than is typical for quasars at redshifts between 6.0 and 6.4. The near-zone transmission profile is consistent with a Lyα damping wing, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.
RESUMEN
A concise, linear synthesis of the Stemona alkaloid (+/-)-neostenine is reported. Key features include an organocopper-mediated bislactone C2-desymmetrization for the stereoselective construction of the cyclohexane-lactone C,D-rings. The assembly of the fused pyrrolo[1,2-a]azepine core was achieved by application of a [5 + 2] maleimide photocycloaddition. A custom FEP flow reactor was used to successfully overcome the scale limitations imposed by a classical immersion well batch reactor. The synthesis was completed in 14 steps from furan, in 9.5% overall yield, without the use of any protecting groups.
Asunto(s)
Alcaloides/síntesis química , Maleimidas/química , Stemonaceae/química , Azepinas/química , Ciclohexanos/química , Furanos/química , Lactonas/química , Modelos Químicos , Fotoquímica , Pirroles/química , EstereoisomerismoRESUMEN
A series of 2-phenyl quinoline-4-carboxylic acid derivatives related to brequinar, an inhibitor of human dihydroorotate dehydrogenase (DHODH), has been prepared and evaluated as inhibitors of DHODH from the malaria parasite Plasmodium falciparum. Brequinar was essentially inactive against PfDHODH (IC(50) 880 microM) whereas several members of the series inhibited PfDHODH. Unexpectedly, replacement of the carboxylic acid required for brequinar to inhibit hDHODH was not essential in the diisopropylamides that inhibited PfDHODH.
Asunto(s)
Compuestos de Bifenilo/química , Compuestos de Bifenilo/farmacología , Inhibidores Enzimáticos/síntesis química , Inhibidores Enzimáticos/farmacología , Malaria/parasitología , Oxidorreductasas actuantes sobre Donantes de Grupo CH-CH/antagonistas & inhibidores , Plasmodium falciparum/enzimología , Alquilación , Aminación , Animales , Benzoquinonas/química , Compuestos de Bifenilo/síntesis química , Ácidos Carboxílicos/química , Dihidroorotato Deshidrogenasa , Inhibidores Enzimáticos/química , Humanos , Concentración 50 Inhibidora , Metilación , Estructura Molecular , Oxidorreductasas actuantes sobre Donantes de Grupo CH-CH/metabolismo , Plasmodium falciparum/efectos de los fármacos , Relación Estructura-ActividadRESUMEN
[reaction: see text] Compact flow reactors have been constructed and optimized to perform continuous organic photochemistry on a large scale. The reactors were constructed from commercially available or customized immersion well equipment combined with UV-transparent, solvent-resistant fluoropolymer (FEP) tubing. The reactors were assessed using the [2 + 2] photocycloaddition of malemide 1 and 1-hexyne forming the cyclobutene product 2 and the intramolecular [5 + 2] photocycloaddition of 3,4-dimethyl-1-pent-4-enylpyrrole-2,5-dione 3 to form the bicyclic azepine 4. The reactors were shown to be capable of producing >500 g of 2 and 175 g of 4 in a continuous 24 h processing period. Due to the facile control of irradiation time, the continuous flow reactor was also shown to be superior to a batch reactor for performing a problematic photochemical reaction on a larger scale.