Efficient synthesis of some novel furo[3,2-<i>e</i>]pyrazolo[3,4-<i>b</i>]pyrazines and related heterocycles

<p>A series of novel 6-functionalized-5-amino-3-methyl-1-phenyl-1<i>H</i>-furo[3,2-<i>e</i>]pyrazolo[3,4-<i>b</i>]pyrazines <b>(4a–c)</b> was synthesized by the reaction of 3-methyl-6-oxo-1-phenyl-6,7-dihydro-1<i>H</i>-pyrazolo[3,4-<i>b</i>]pyrazine-5-carbonitrile <b>(2)</b> with α-halocarbonyl compounds such as: diethyl 2-bromomalonate, phenacyl bromide and chloroacetone. Cyclocondensation of the amino benzoyl <b>4b</b> with diethyl malonate yielded the oxopyridine carboxylate derivative <b>5</b>. Also, the starting intermediate amino ester compound <b>4a</b> was allowed to react with ethanol amine to afford the hydroxyethyl caboxamide derivative <b>6</b>. Furthermore, hydrazinolysis of the amino ester <b>4a</b> afforded the corresponding amino carbohydrazide <b>7</b> which was used as a versatile precursor for synthesis of other heterocyclic compounds attached or fused to the furopyrazolopyrazine moiety. The chemical structures of the newly synthesized compounds were confirmed on the basis of elemental and spectral analyses containing FT-IR, ¹H NMR, ¹³C NMR, and mass spectrometry hoping these molecules should allow us to investigate their pharmacological activities in the future study.</p

Synthesis, reactions, and antioxidant activity of 3-(pyrrol-1-yl)-4,6-dimethyl selenolo[2,3-<i>b</i>]pyridine derivatives

<p>Ethyl 4,6-dimethyl-3-(pyrrol-1-yl) selenolo[2,3-<i>b</i>]pyridine-2-carboxylate <b>(2)</b> was synthesized by the reaction of previously prepared ethyl 3-amino-4,6-dimethyl selenolo[2,3-<i>b</i>]pyridine-2-carboxylate <b>(1)</b> with 2,5-dimethoxytetrahydrofuran in acetic acid. The pyrrolyl ester <b>(2)</b> was converted into the corresponding carbohydrazide <b>3</b> which reacted with acetyl acetone, aromatic aldehydes, carbon disulfide in pyridine, and sodium nitrite to afford the corresponding dimethyl pyrazolyl <b>4</b>, arylidene carbohydrazides <b>5a–d</b>, oxadiazolyl thiole <b>6,</b> and caboazide compound <b>8,</b> respectively. The carboazide <b>8</b> reacted with different alcohols and amines to give the corresponding carbamates <b>9a–c</b> and the aryl urea derivatives <b>10a–d</b>. Heating of carboazide <b>8</b> in dry xylene afforded the pyridoselenolo-pyrrolopyrazinone <b>11</b>. The latter compound was used as a versatile starting precursor for synthesis of other pyridoselenolo-pyrrolopyrazine compounds. The newly synthesized compounds and their derivatives were characterized by elemental analysis and spectroscopy (IR, ¹H-NMR, and mass spectra). Some of the newly synthesized pyrrolyl selenolopyridine compounds showed remarkable antioxidant activity compared to ascorbic acid.</p