Tin tetrachloride-induced π-cyclizations of glycine cation equivalents to substituted pipecolic acid derivatives
摘要:
Cationic pi-cyclization reactions of N-(3-alkenyl)-N-(methoxycarbonyl)acetoxyglycine esters induced by tin tetrachloride in dichloromethane are described. Reactions started and quenched with water at -78-degrees-C mainly yield cis-4-hydroxypipecolic esters, whereas reactions quenched after warm-up to room temperature provide trans-4-chloropipecolic esters as major products. A mechanistic scheme is advanced which adequately explains these results. The essentials are a rapid cationic aza-Cope equilibrium of the incipient iminium cation, and participation of the ester moiety through formation of a relatively stable bicyclic dioxycarbenium cation as pivotal intermediate.
N-Alkenyl and cycloalkyl carbamates as dual acting histamine H3 and H4 receptor ligands
摘要:
Previous studies have shown that several imidazole derivatives posses affinity to histamine H-3 and H-4 receptors. Continuing our study on structural requirements responsible for affinity and selectivity for H-3/H-4 receptor subtypes, two series of 3-(1H-imidazol-4-yl) propyl carbamates were prepared: a series of unsaturated alkyl derivatives (1-9) and a series possessing a cycloalkyl group different distances to the carbamate moiety (10-13). The compounds were tested for their affinities at the human histamine H3 receptor, stably expressed in CHO-K1 cells. Compounds 1, 2, 5-7, 10-13 were investigated for their affinities at the human histamine H-4 receptor co-expressed with G alpha(i2) and G beta(1)gamma(2) subunits in Sf9 cells. To expand the pharmacological profile, compounds were further tested for their H3 receptor antagonist activity on guinea pig ileum and in vivo after oral administration to mice. All tested compounds exhibited good affinity for the human histamine H-3 receptor with K-i values in the range from 14 to 194 nM. All compounds were active in vivo after peroral administration (p.o.) to Swiss mice, thus demonstrating their ability to cross the blood-brain barrier. The most potent H-3 receptor ligand of these series was compound 5, 3-(1H-imidazol-4-yl) propyl pent-4-enylcarbamate with the highest affinity (K-i = 14 nM). Additionally, compound 3 showed remarkable central nervous system (CNS) H3R activity, increasing the N-tau-methylhistamine levels in mice with an ED50 value of 0.55 mg/kg, p.o. evidencing therefore, a twofold increase of inverse agonist/antagonist potency compared to the reference inverse agonist/antagonist thioperamide. In this study, the imidazole propyloxy carbamate moiety was kept constant. The different lipophilic moieties connected to the carbamate functionality in the eastern part of the molecule had a range of influences on the human H-4 receptor affinity (154-1326 nM). (C) 2011 Elsevier Ltd. All rights reserved.
Palladium-catalyzed oxidation of amino alkenes to cyclic imines or enamines and amino ketones
作者:B. Pugin、L. M. Venanzi
DOI:10.1021/ja00361a023
日期:1983.11
n NH 2 (n=3,4) se cyclisent en pyrrolines-1 ou tetrahydro-3,4,5,6 pyridines dans les conditions du procede Wacker. Les aminoalcenes avec un groupe amino secondaire donnent les imines cycliques correspondantes, tandis que les alcenes avec un groupe amino tertiaire donnent des aminocetones
Lesaminoalcenes du type CH 2 =CH(CH 2 ) n NH 2 (n=3,4) se cyclisent en pyrrolines-1 ou tetrahydro-3,4,5,6 pyridines dans les conditions du procede Wacker。Lesaminoalcenes avec un groupe amino secondaire donnent les imines cycliquesrespondantes, tandis que les alcenes avec un groupeamino tertiaire donnent desaminocetones
Catalyst-Controlled Nickel-Catalyzed Intramolecular <i>endo</i>-Selective C–H Cyclization of Benzimidazoles with Alkenes
作者:Zi-Jian Liu、Jiang-Fei Li、Feng-Ping Zhang、Xue-Tao Xu、Mengchun Ye
DOI:10.1021/acs.orglett.2c04012
日期:2023.1.20
Compared with the widely explored exo-selective C–H cyclization, transition metal-catalyzed endo-selective C–H cyclization of benzimidazoles with alkenes has been a formidable challenge. Previous efforts mainly rely on substrate-controlled methods, rendering the product complexity restricted. Herein we report a catalyst-controlled method to facilitate endo-cyclization, in which a bulky N-heterocyclic
Epoxidation of Primary and Secondary Alkenylammonium Salts with Dimethyldioxirane, Methyl(trifluoromethyl)dioxirane, and m-Chloroperbenzoic Acid. A General Synthetic Route to Epoxyalkylamines
作者:Gregorio Asensio、Rossella Mello、Carmen Boix-Bernardini、Maria Elena Gonzalez-Nunez、Gloria Castellano
DOI:10.1021/jo00117a020
日期:1995.6
Selective syn-epoxidation of C=C double bonds in primary and secondary alkenylammonium arenesulfonate salts 3H(+), to give the corresponding epoxyalkylammonium salts 4H(+), has been achieved by reaction with electrophilic O-transfer reagents such as m-CPBA, methyl(trifluoromethyl)dioxirane (TFDO), and dimethyldioxirane (DMDO). Epoxyalkylamines 4 are easily obtained in high yields from the corresponding epoxyalkylammonium salts 4H(+) by simple deprotonation with sodium carbonate. The ammonium group deactivates the C=C double bond, and hence the epoxidation rate is slower than in the case of simple olefins. II-Bonding interaction between the ammonium group and the O-transfer reagent(m-CPBA and DMDO) in the transition state is claimed to account for the rate enhancement and diastereoselectivity observed when the necessary conformational requirements are established. The allylic ammonium group is shown to be very efficient in directing the epoxidation with m-CPBA and DMDO on the syn-diastereoface.
Anticonvulsant properties of histamine H3 receptor ligands belonging to N-substituted carbamates of imidazopropanol
Ligands targeting central histamine H-3 receptors (H(3)Rs) for epilepsy might be a promising therapeutic approach. Therefore, the previously described and structurally strongly related imidazole-based derivatives belonging to carbamate class with high H3R in vitro affinity, in-vivo antagonist potency, and H3R selectivity profile were investigated on their anticonvulsant activity in maximal electroshock (MES)-induced and pentylenetetrazole (PTZ)-kindled seizure models in Wistar rats. The effects of systemic injection of H3R ligands 1-13 on MES-induced and PTZ-kindled seizures were screened and evaluated against the reference antiepileptic drug (AED) Phenytoin (PHT) and the standard histamine H3R inverse agonist/antagonist Thioperamide (THP) to determine their potential as new antiepileptic drugs. Following administration of the H3R ligands 1-13 (5, 10 and 15 mg/kg, ip) there was a significant dose dependent reduction in MES-induced seizure duration. The protective action observed for the pentenyl carbamate derivative 4, the most protective H3R ligand among 1-13, was significantly higher (P<0.05) than that of standard H3R antagonist THP, and was reversed when rats were pretreated with the selective H3R agonist R-(alpha)-methyl-histamine (RAMH) (10 mg/kg), or with the CNS penetrant H1R antagonist Pyrilamine (PYR) (10 mg/kg). In addition, subeffective dose of H3R ligand 4 (5 mg/kg, ip) significantly potentiated the protective action in rats pretreated with PHT (5 mg/kg, ip), a dose without appreciable protective effect when given alone. In contrast, pretreatment with H3R ligand 4 (10 mg/kg ip) failed to modify PTZ-kindled convulsion, whereas the reference drug PHT was found to fully protect PTZ-induced seizure. These results indicate that some of the investigated imidazole-based H3R ligands 1-13 may be of future therapeutic value in epilepsy. (C) 2013 Elsevier Ltd. All rights reserved.