Ahmed A. Kassem

Microwave Irradiation for Accelerating Organic Reactions. Part I: Three-, Four- and Five-Membered Heterocycles

Publisher Summary The microwave (MW) region of the electromagnetic spectrum lies at frequencies from 0.3 to 300 GHz. The energy transitions in the MW region are enough to cause bond rotation. Recently, microwave irradiation (MWI) has attracted much attention as a tool of preference in achieving and/or accelerating organic reactions. When matter is irradiated with MW, the ability of a molecule to absorb MWI is a function of two main mechanisms. These are namely molecular polarizability which in turn is a function of its dipole moment, and its ionic conduction. This chapter reviews the literature on the synthesis and reactions of three-, four- and five-membered heterocycles using MWI. It is divided according to the order of increasing size of the heterocycles and the number of heteroatoms. Each type is described according to their methods of preparation of the desired ring and by their reactions. Heterocycles having fused benzene rings have also been discussed.

Regioselectivity in the glycosylation of 5-(3-chlorobenzo[b]thien-2-yl)-4H-1,2,4-triazole-3-thiol

The glycosylation of 5-(3-chlorobenzo[b]thien-2-yl)-4H-1,2,4-triazole-3-thiol (1) and its 3-benzylsulfanyl and 3-methylsulfanyl derivatives with different glycosyl halides 2-4 has been studied in presence of base. The S-glycosides 5-7 were obtained in the presence of triethylamine, whereas the respective S,N(4)-bis(glycosyl) derivatives 8-10 were synthesized in the presence of potassium carbonate; the S,N(2)-bis(glycosyl) isomer 11 could also be isolated in the case of the galactosyl analog. Similarly, after protecting 1 as 3-benzyl(methyl)sulfanyl derivatives 12 or 13, the N(4)-glycosyl analogs 14-19 as well as minor amounts of S,N(2)-bis(galactosyl) isomers 20 and 21 were formed. The theoretical calculations using AM1 semiempirical methods agreed with the experimental results. Microwave irradiation (MWI) led to higher yields in much less time than the conventional methods, and no change in regioselectivity has been noticed.

Selective cyclisation of 2,3,4,5-tetra-O-acetylgalactaric acid bis[alkylthio(thiocarbonyl)]hydrazides to saccharide 1,3,4-oxadiazole, thiadiazole, and thiadiazoline derivatives

The syntheses of galactaric acid acetate bis[alkylthio-(thiocarbonyl)]hydrazides (1,2) are described. Selective cyclisation of both hydrazide 1 and 2 was investigated. Using phosphorous oxychloride as a cyclising agent, loss of water produced 1,2,3,4-tetra-O-acetyl-1,4-bis(5-S-methyl or benzyl)-1,3,4-thiadiazol-2-yl)galacto-tetritol (3) or (4). Use of thionyl chloride lead to dehydrosulfurization and gave 1,2,3,4-tetra-O-acetyl-1,4-bis(5-S-methyl or benzyl)-1,3,4-oxadiazol-2-yl)galacto-tetritol (5) or (6). Finally, with triethyl orthoformate as the cyclising agent, compound 1 or 2 gave 3,3′-(2,3,4,5-tetra-O-acetylgalactar-1,6-dioyl)-bis-[(2-ethoxy-2,3-dihydro-5-S-methyl or benzyl)-1,3,4-thia-diazole] (7) or (8).

Leptin in pediatrics: A hormone from adipocyte that wheels several functions in children

The protein leptin, a pleiotropic hormone regulates appetite and energy balance of the body and plays important roles in controlling linear growth, pubertal development, cardiovascular function, and immunity. Recent findings in the understanding of the structure, functional roles, and clinical significance of conditions with increased and decreased leptin secretion are summarized. Balance between leptin and other hormones is significantly regulated by nutritional status. This balance influences many organ systems, including the brain, liver, and skeletal muscle, to mediate the essential adaptation process. The aim of this review is to summarize the possible physiological functions of leptin and its signaling pathways during childhood and adolescence including control of food intake, energy regulation, growth and puberty, and immunity. Moreover, its secretion and possible roles in the adaptation process during different disease states (obesity, malnutrition, eating disorders, delayed puberty, congenital heart diseases and hepatic disorders) are discussed. The clinical manifestations and the successful management of patients with genetic leptin deficiency and the application of leptin therapy in other diseases including lipodystrophy, states with severe insulin resistance, and diabetes mellitus are discussed.

Novel Regioselective Formation of S- and N-Hydroxyl-Alkyls of 5-(3-Chlorobenzo[b]Thien-2-yl)-3-Mercapto-4H-1,2,4-Triazole and A Facile Synthesis of Triazolo-Thiazoles and Thiazolo-Triazoles. Role of Catalyst and Microwave

Regioselective alkylation of 5-(3-chlorobenzo[b]thien-2-yl)-4H-1,2,4-triazole (1) with hydroxy alkylating agents 2, 3, 13, and the 2,3-O-isopropylidene-1-O-(p-tolylsulfonyl)-glycerol (10) afforded the corresponding S-alkylated derivatives 6, 7, 11, and 14 under both conventional and microwave irradiation conditions; bentonite as a solid support gave better results, with no change in regioselectivity. A facile intramolecular dehydrative ring closure of 6, 7, 11, and 14 using K2CO3 in DMF afforded the corresponding fused triazolo-thiazines and thiazolo-triazole 17–19. The isopropylidenes and acetyl derivatives of the products were prepared.

Synthesis and Reactions of Acenaphthenequinones-Part-2. The Reactions of Acenaphthenequinones

The reactions of acenaphthenequinone and its derivatives with different nucleophiles, organic and inorganic reagents are reviewed. This survey also covers their oxidation and reduction reactions, in addition to many known reactions such as Friedel Crafts, Diels-Alder, bromination and thiolation.

Study of the thermal stabilities of some polymeric schiff-bases containing sulphur

Abstract The relationship of the thermal stabilities of some polymeric Schiff-bases to their chemical structures was studied by using thermogravimetric analysis and differential thermal analysis. Polymeric Schiff-bases were prepared by the condensation of 5,5′-methylene-bis-salicylaldehyde, terephthalaldehyde, di( p -formylphenyl) terephthalate or di( p -acetylphenyl) terephthalate with various diamines containing sulphur, such as thiocarbohydrazide, bis (4-aminophenyl) sulphone, 4,4′-diaminostilbene-2,2′-disulphonic acid and 3,5-diaminobenzene sulphonic acid. Two monomeric prototypes of these polymeric Schiff-bases were prepared in order to compare their thermal stabilities with the corresponding polymers.

Synthesis and Properties of Some Schiff-Base Polymers Containing Sulfur

Abstract Condensation of 5,5′-methylene-bis-salicylaldehyde with thiocarbohydrazide, bis(4-aminophenyl) sulfone, 4,4′-diaminostilbene-2,2′-disulfonic acid or 3,5-diaminobenzenesulfonic acid gave the corresponding polymeric schiff-bases (1, 2, 3, or 4). Also, condensation of terephthalaldehyde with thiocarbohydrazide or bis(4-aminophenyl) sulfone produced the schiff base polymers (5 or 6). Finally, condensation of di(p-formylphenyl) terephthalate or di(p-acetylphenyl) terephthalate produced the polymers (7, 8). Structures of these polymers (1 − 8), their properties, viscosities measurements and the effect of various reaction conditions on the yield percent are studied. These variable conditions showed no effect on the molecular weight of the present schiff polymers.

New Synthesis of Monomeric and Polymeric Saccharide bis-Hydrazide Diamines Salts. Reaction of 2, 3, 4, 5-Tetra-O-acetyl Galactaric Acid bis-Hydrazides with Different Diamines

Abstract Reaction of 1-(2,3,4,5-tetra-o-acetylgalactaroy1)bis-2-[thiomethyl or thiobenzy1(thiocarbony1)]hydrazine 1 or 2 with different bifunctional amines [piperazine (PPZ), tetraethyl-ethylenediamine (TEED), tetramethylethylenediamine (TMED), and tetramethyl propanediamine (TMPD)] at different hydrazide/diamine ratios in methanol, gave the corresponding monomeric and polymeric bis-hydrazide salts. Elucidation of the structures of compounds prepared are discussed and mechanistic pathways for their formation are proposed.

Lane departure warning tracking system based on score mechanism

This paper presents a new lane tracking algorithm for the lane departure warning system without using Kalman filter. The system is capable of extracting the true lane boundaries from all detected lines including noise in the frame and estimates its future position. The new algorithm uses the score mechanism to trace the appearance of lines in previous frames using a score variable which indicates the number of frame lines that have been detected and scores state of each line (increasing or decreasing). The lateral shift is calculated from prior knowledge of lane boundary positions in previous frames. Moreover, the algorithm introduces a hysteresis loop of line score varying the number of predicted frames for line position which has a significant impact in smoothing and stabilizing the tracking process.