M. A. E. Shaban

Heterocycles from saccharide hydrazones : Part I. Saccharide 1,3,4-oxadiazoles

Abstract Oxidation, with iodine-mercuric oxide, of acetylated saccharide aroylhydrazones and of aromatic aldehyde hydrazones yields 5-aryl-2-(polyacetoxyalkyl)-1,3,4-oxadiazoles and 2,5-diaryl-1,3,4-oxadiazoles, respectively. On de- O -acetylation, saccharide oxadiazole acetates rearrange to the tautomeric, cyclic iminolactones which, on reacetylation, regenerate the starting oxadiazoles. Attempted dehydration of saccharide acetyl- and benzoyl-hydrazones by treatment with boiling acetic anhydride under reflux resulted in the formation of peracetylated N,N -diacetylhydrazones and- N -acetyl- N -benzoylhydrazones, respectively.

The Chemistry of 1,2,4-Triazolopyrimidines I: 1,2,4-Triazolo[4,3-a]Pyrimidines

Publisher Summary This chapter reviews the chemistry of 1,2,4-triazolopyrimidines. The chapter is devoted to surveying the chemistry of one of the four possible systems of this class of compounds—namely, 1,2,4-triazolo[4,3-a]pyrimidin. The chapter focuses on the chemistry of 1,2,4-triazolo[1,5-c]pyrimidines. This chapter discusses the introduction, synthesis, reactions, spectral properties, and applications of 1,2,4-triazolopyrimidines 11: 1,2,4-triazolo[4,3-c]pyrimidines. It also illustrates that many members of the 1,2,4-triazoIo[4,3-c]pyrimidines are shown to possess very interesting biological activities and medicinal applications. The chapter concludes by discussing that 1,2,4-triazoIo[4,3-c]pyrimidines have been synthesized using several general approaches: (1)annulation of the 1,2,4-triazole ring onto a pyrimidine structure; (2) annulation of the pyrimidine ring onto a 1,2,4-triazole structure; (3) concurrent formation of both of the 1,2,4-triazole and pyrimidine rings; and (4) rearrangement of pyrimido[5,4-e]l,2,4-triazines.

Synthesis and Biological Activities of Condensed Heterocyclo[n,m-a,b, or c]Quinazolines

Publisher Summary The synthesis and biological activities of title compounds are systematically arranged according to the complexity of the heterocyclic ring directly fused to the pyrimidine ring of the quinazoline nucleus (irrespective of other rings that might be fused to it), starting with those having one nitrogen atom in a three-membered ring and going to more complex ones. The heterocycles have been arranged according to the type of their heteroatom in the following order: nitrogen, oxygen, sulfur, and selenium. Consideration has been given to the alternative nomenclature of some heterocyclo- quinazolines, also known as quinazolinoheterocycles, in order to comply with the nomenclature rules of the IUPAC. The diverse biological activities of the title compounds have certainly contributed to the extensive efforts directed towards their synthesis.

Synthesis of condensed 1,2,4-triazolo [3,4-z] heterocycles

Publisher Summary This chapter discusses the synthesis of condensed 1,2,4-triazolo[3,4-z]- heterocycles. The synthesis of condensed 1,2,4-triazolo[3,4-z]- heterocycles is arranged according to the complexity of the ring directly fused to the 1,2,4-triazole nucleus (irrespective of other rings that might be fused to it) beginning with those rings having one nitrogen atom in a five-membered ring and proceeding with those that are more complex. The heterocycles are arranged in the following order according to their types of heteroatoms: nitrogen, oxygen, sulfur, and other elements. Consideration is given to the possible alternative nomenclature of some 1,2,4- triazoles[3,4-z]heterocycles such as heterocyclo[n,m-c] 1,2,4-triazoles (n,m are numbers indicating linkage positions of the heterocycle to the traizole ring) in order to comply with the nomenclature rules of the IUPAC.

Synthesis of carbohydrate-containing polyamides and study of their properties☆

Abstract Carbohydrate-containing polyamides were prepared using low-temperature solution polycondensation of 2,3,4,5-tetra-O-acetylgalactaroyl dichloride (3) with various aromatic and aliphatic diamines viz. p- phenylenediamine ( 4 ) ; m-phenylenediamine; benzidine; 4,4′-diaminodiphenylmethane; 1,5-diaminoanthraquinone; 2,6-diaminoanthraquinone; 4,4′-diaminodicyclohexylmethane; hexamethylenediamine; and ethylenediamine (12). The four O-acetyl groups in 3 protect the hydroxyl functions and give good solubility as a result of increasing lipophilicity. The optimum conditions for the best yield and viscosity of the polyamide were determined by study of the factors affecting the polycondensation. These conditions for reaction of 3 with 4 were reached with reactant concentrations of 0.5 mol/l at −10°. On the other hand, the optimum conditions for reaction of 3 with 12 involved concentrations of 1.0 mol/l at 0°. Polyamides containing the unacetylated carbohydrate chains were obtained by de-O-acetylation of the synthesized acetylated carbohydrate-containing polyamides. Structures of the acetylated and de-O-acetylated carbohydrate-containing polyamides were confirmed by elemental analysis, i.r. and 1H-NMR spectroscopy. Their thermal degradations were studied by differential thermal analysis and thermogravimetric analysis.

The synthesis of 3-(alditol-1-yl)-1,2,4-triazolo[3,4-a]phthalazines

Abstract Condensation of 1-hydrazinophthalazine (hydralazine) with d -lyxose, d -ribose, d -xylose, d -mannose, and l -rhamnose gave the corresponding aldehydo -sugar phthalazin-l-ylhydrazones. d D-Arabinose and d -galactose, on the other hand, gave the corresponding 3-(alditol-l-yl)-1,2,4-triazolo[3,4- a ]phthalazines through the autodehydrogenative cyclization of the hydrazones. A rationale for this difference is discussed. Acetylation of the latter gave the poly- O -acetyl derivatives. Catalytic, dehydrogenative cyclization with palladium-on-charcoal, or acetylation, transforms the hydrazones into the triazolophthalazines, or their acetates. The mass spectra of the synthesized compounds were discussed.

Synthesis of 1,3,4-Thiadiazole and 1,2,4-Triazole acyclo C-Nucleosides

Abstract Reaction of 4-arylthiosemicarbazides (1) with 2,3,4,5-tetra-O-acetylgalactaroyl dichloride (2) gave the corresponding 2,3,4,5-tetra-O-acetylgalactaroyl-bis(4-aryl-thiosemicarbazides (3). The latter compounds underwent dehydrative cyclization by heating with phosphoryl chloride to give 1,2,3,4-tetra-O-acetyl-1,4-bis(5-arylamino-1,3,4-thiadiazol-2-yl)galacto-tetritols (4) which afforded, upon de-O-acetylation with methanolic ammonia, the corresponding 1,4-bis(5-arylamino-1,3,4-thiadiazol-2-yl)-galacto-tetritols (5). Compounds 3 were also cyclodehydrated, in a different way, with concomitant de-O-acetylation upon treatment with ethanolic sodium ethoxide to give 1,4-bis(4-aryl-5-thioxo-1,2,4-triazol-3-yl)galacto-tetritols (6). Acetylation of 6 with acetic anhydride in the presence of pyridine afforded 1,2,3,4-tetra-O-acetyl-1,4-bis(1-acetyl-4-aryl-5-thioxo-1,2,4-triazol-3yl)galacto-tetritols (7). Compounds 3a, 3b and 6a-c showed no antibacterial activity against Bacillus subtilis, Escherichia coli, P...

Cyclization of aldonic acid aroylhydrazides to 1,3,4-oxadiazoline derivatives

Abstract d -Glucono-1,5-lactone reacts with aroylhydrazines to give the corresponding 1-aroyl-2- d -gluconylhydrazines. Condensative cyclization of these compounds using triethyl orthoformate gave the corresponding 5-aryl-2-ethoxy-3- d -gluconyl-2,3-dihydro-1,3,4-oxadiazoles.

Cyclization of 2,3,4,5-tetra-O-acetylgalactaric bis-(aroylhydrazides) to saccharide bis(1,3,4-oxadiazolyl) derivatives

Abstract Condensation of 2,3,4,5-tetra-O-acetylgalactaroyl dichloride with two equivalents of various aroylhydrazines gave the corresponding 2,3,4,5-tetra-O-acetylgalactaric bis(aroylhydrazides). Condensative and dehydrative cyclization of these bis(hydrazides) with triethyl orthoformate and phosphoryl chloride, respectively, gave the corresponding 3,3′-(2,3,4,5-tetra-O-acetylgalactar-1,6-dioyl)-bis(5-aryl-2-ethoxy-2,3-dihydro-1,3,4-oxadiazole) and 1,2,3,4-tetra-O-acetyl-1,4-bis(5-aryl-1,3,4-oxadiazol-2-yl)-galacto-tetritols. The elucidation of the structure of the compounds prepared is discussed and mechanistic pathways for their formation are proposed.

Synthesis and characterization of carbohydrate-containing copolyhydrazides and copolyoxadiazoles

Abstract Carbohydrate-containing copolyhydrazides were synthesized by the reaction of 2,3,4,5-tetra-O-acetyl galactaroyl dichloride with typical dibasic aromatic and aliphatic acid dihydrazides, viz. terephthaloyl dihydrazide (4) succinoyl dihydrazide and oxalyldihydrazide (6), using low temperature solution polycondensation in N,N-dimethylacetamide. The maximum viscosity and yield of the copolyhydrazide derived from 4 were obtained for reactant concentration of 0.5 mol/l at −10°. The optimum conditions for the copolyhydrazide derived from 6 were obtained at reactant concentration of 1.0 mol/l at −5°. Copolyhydrazides containing unacetylated carbohydrate chains were obtained by de-O-acetylation of the acetylated polymers with methanolic ammonia. Copoly{1-[2-(2,3,4,5-tetra-O-acetyl-galacto-tetritoldi-1,4-yl)-5-(1,3,4-oxadizol-di-2,5-yl)]-4-[2-(1,3,4- oxadiazol-di-2,5-yl)-benzene]} was prepared by dehydrative cyclization of the corresponding copolyhydrazide using thionyl chloride. Structures of the synthesized polymers were confirmed by elemental analysis, i.r., and 1H-NMR. Thermal degradations of these polymers were studied by differential thermal analysis and thermogravimetric analysis.