Hassan A. Albar

Chemistry of the Genus Plectranthus

This review presents the phytochemical constituents of the genus Plectranthus reported up to 1999. Only a tetrameric derivative of caffeic acid was isolated from P. japonicus, but a group of long-chain alkylphenols, of possible taxonomic significance in the genus, was also isolated. As a genus of the subfamily Nepetoideae, Plectranthus is free from iridoid glycosides and rich in essential oil (i.e. > 0.5% volatile oil on a dry weight basis). Diterpenoids are the more common secondary metabolites in Plectranthus. The majority of them are highly modified abietanoids. This seems to be similar to the pattern of diterpenoids observed for Salvia, but no clerodane diterpenoids were found in Plectranthus.

Facile Syntheses of Bi-1,2,4-triazoles via hydrazonyl halides

Reaction of oxalodihydrazonyl dihalides 1 with sodium azide afforded the corresponding di-azides 2. Reduction of the latter with LiAlH4 yielded the diamidrazones 4 which react with acyl halides to give the bi-1,2,4-triazoles 5. The latter products were alternatively prepared by reaction of 2 with triphenylphosphine to give the phosphinimines 6 followed by treatment of the latter with acyl halides.

Cycloaddition of diphenylnitrilimine to coumarins. The synthesis of 3a, 9b-dihydro-4-oxo-1H-benzopyrano [4,3-c]pyrazole derivatives

Abstract The cycloaddition of diphenylnitrilimine to a series of coumarins occurs with the same regioselectivity in all cases, regardless the nature of the substituent present, to yield the corresponding 3a,9b-dihydro-4-oxo-lH-benzopyrano [4,3-c]pyrazoles 4 a–f. Dehydrogenation of 4a yields 4-oxo-1H-benzopyrano [4,3-c]-pyrazole 6 . In ethanolic sodium ethoxide solution, the reaction between coumarin and diphenylnitrilimine precursor, namely N-phenylbenzohydrazidoyl chloride 1 , affords no cycloadducts, but yields o-(β-ethoxycarbonylvinyl)phenyl N-phenylbenzohydrazidate 10 . The regiochemistry of the cycloadducts 4 a–f and the reaction sequence leading to 10 are outlined. The structures of the products have been established by spectroscopic methods and independent syntheses wherever possible.

Carbon-supported PtCo 2 Ni 2 alloy with enhanced activity and stability for oxygen reduction

The commercialization of proton exchange membrane fuel cells (PEMFCs) is still restricted by the well-known dilemma, that is, the heavy dependence of using expensive plantinum (Pt) catalyst to negotiate the sluggish oxygen reduction reaction (ORR) kinetics in fuel cell cathodes. Here, a carbon-supported PtCo2Ni2 alloy catalyst with low Pt usage was synthesized via a simple method, which exhibited exceptional ORR activity with a more positive half-wave potential (E1/2) ∼57 mV, which was more positive than the state-of-the-art Pt/C catalysts. Moreover, the alloy catalyst performs excellent durability after 10,000 harsh cycles compared with that of Pt/C catalyst in acidic solution, which may be developed as a promising alternative for Ptbased catalysts in fuel cell technology.摘要近年来, 质子交换膜燃料电池由于高成本严重阻碍了其商业化进程, 而目前催化阴极氧气还原反应最高效的催化剂仍然是昂贵的铂催化剂, 因此设计、 开发制备少铂、 高效、 稳定的催化剂是目前此领域研究的热点. 本论文利用一种简便的制备方法得到了碳负载的铂钴镍(摩尔比=1:2:2)三元合金纳米颗粒催化剂, 这种合金化催化剂在改变铂电子结构的同时, 大大降低了贵金属铂的用量. 电化学测试结果显示这种多元合金催化剂的半波电势与商业铂碳相比提高了约57 mV, 而且优于同体系制备的二元合金催化剂和其他组分三元合金催化剂. 此外, 在酸性电解质溶液中, 此催化剂表现出更优异的稳定性. 在燃料电池技术领域, 这种多元合金化催化剂很可能在将来发展成新电催化剂来替代铂材料.

Synthesis of Novel Cyclic Benzenesulfonylurea and Thiourea Derivatives

Treatment of the pyrazoline derivatives (1-6) with isocyanates or isothiocyanates afforded ureas (7-18) and thioureas (19-32) in a good yield. Subsequent treatment of the benzenesulfonylthioureas (19-32) with f - and g -halogenocarbonyl compounds gave the corresponding thiazolidines (33-41) and 1,3-thiazinones (42-46) respectively. When urea derivatives (7-18) were reacted with dimethyl malonate in sodium ethoxide, they gave the corresponding pyrazolebarbiturate derivatives (53-56) . The structure of the isolated product were determined by the spectral methods.

Chemical composition of the essential oil of Plectranthus tenuiflorus from Saudi Arabia

ABSTRACT An oil of Plectranthus tenuiflorus produced from plants harvested in Saudi Arabia was analyzed by GC/MS. The principal component of the oil was found to be thymol (85.3%).

Regioselectivity in the reactions of diphenylnitrilimine with coumarin and chromone

Abstract The cycloaddition of diphenylnitrilimine with coumarin and chromone gave the cycloadducts 4 and 5 respectively. The structures of these products were based on elemental and spectral analyses and alternate synthesis. The orientations of the cycloaddition are interpreted in terms of FMO theory.

C-(α-d-Glucopyranosyl)-phenyldiazomethanes—irreversible inhibitors of α-glucosidase

Several C-(α-d-glucopyranosyl)-phenyldiazomethanes, with different substituent groups at the para-position of the phenyl ring, were prepared. The stabilities of these diazo compounds were investigated through NMR and UV monitoring. The para-cyano substituted diazo compound was found to be stable in neutral media (pH 7.0 buffer) and could be isolated. Inhibitory activity investigations indicated that this compound is an irreversible inhibitor against α-glucosidase from Saccharomyces cerevisiae.

Modern Friedel–Crafts Chemistry. Part 24.† Alkylation of Benzene with 1,2-Dibromo-3-chloro-2-methylpropane in the Presence of Lewis and Brønsted Acid Catalysts‡

The major alkylation products of benzene with 1,2-dibromo-3-chloro-2-methylpropane are 1-X-2-methyl- 3,3-diphenylpropane (X=Cl, Br) with AlCl 3 and 1,4-bis-(1-bromo-3-chloro-2-methylpropyl)benzene with AlCl 3 –CH 3 NO 2 or K10 montmorillonite (K10 Clay); minor products include di- and tri-phenylated butanes and/or 2-methyl- 1-phenylindane.

Synthesis of Novel Spiro and Fused Cyclopenta[c]-pyrazole and -pyrimidine Derivatives

Condensation of diarylmethylidenecyclopentanes with hydrazine, hydroxylamine and thiourea derivatives afford the corresponding fused pyrazoles, oxazoles and pyrimidines.