X-ray crystal structure data for the title compound dihydrobenzofuryl-pyrazolo[4,3-d]pyrimidin- 7-one (2) reveal that the two bicyclic heteroaryl systems are virtually coplanar along their joint C (5)-C(11) axis with an interplanar angle of 1.13°. This planar conformation is held by an intramolecular hydrogen bond between the pyrimidinone N(6)-H and the O(17) lone pair of the dihydrobenzofuryl moiety. The spatial interatomic distance for O(17)-N(6), determined as 2.04 Å, favours this H-bridge.
The synthesis and spectral properties (IR, MS, NMR) of a substituted 5-(2,3-dihydro-7- benzofuryl)pyrazolo[4,3-d]pyrimidin-7-one (2), an analog of Viagra® (1), are described. The generally applicable route involves interaction of 2,3-dihydro-7-benzofuranoyl chloride (3) with 4-amino-l-methyl-3-propyl-5-pyrazolecarboxamide (4), and the resulting bis-amide (5) is cyclized to the corresponding substituted pyrazolo[4,3-d]pyrimidin-7-one (6). Chlorosulfonylation of 6, followed by treatment with 1-methylpiperazine, furnished the title compound 2 (named Biagra). Preliminary experiments “associated with the erectile process” on rats lend evidence of greater potency of Biagra (2) as compared to Viagra® (1).
X-ray crystal structure data for the substituted 5-(2,3-dihydro-7-benzofuryl)-2-methylpyrazolo[ 4,3-d]pyrimidin-7-one (3) reveal that the two bicyclic heteroaryl systems show no coplanarity along their joint C (5) - C (11) axis with an interplanar angle of 9.6°. Nonetheless, the spatial interatomic distance for O(17)-N(6), determined as 2.73 A, allows the formation of a relatively weak intramolecular hydrogen bond between the pyrimidinone N(6)-H and the O(17) lone pair of the dihydrobenzofuryl moiety.
New model 1,2,4-triazino[6,5-h]quinolines 8a - c are prepared by oxidative cyclization of the respective N-(quinolin-8-yl)amidrazone precursors 7a - c using copper(II) chloride. Interestingly, the cyclized products 8a - c were found to be arylated at N1 position. Analytical and spectral (MS, NMR) data of the title products are in compliance with the allocated structures.
Ethyl 7,8-diamino-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylate (6) and its free acid 7 are prepared by chemical reduction of the respective 7-azido-8-nitroquinoline 5. Consecutive nucleophilic addition and cyclocondensation reactions of 6 with α-acetyl-N-arylhydrazonoyl chlorides 8a - c in ethanol and triethylamine are site-selective and yield the corresponding 3-(aryldiazinyl)- 2-methylpyrido[2,3- f ]quinoxalines 10a - c. Analytical and spectral (IR, MS, NMR) data of 6, 7, and 10a - c are in conformity with the assigned structures.
A Selected set of 2-(quinolin-2-yl)-1,3-oxazepino[7,6-b]indoles 4a–d and dihydroacenaphtho[1,2-f][1,3]oxazepine 5 have been prepared via 1,4-dipolar cycloaddition reaction involving 1-phenylimidazo[1,5-a]quinoline, dimethyl acetylenedicarboxylate, and N-(substituted)isatins or acenaphthoquinone. Structures of the new heterocycles 4a–d and 5 are supported by NMR and HRMS spectral data, and confirmed by single-crystal X-ray crystallography for 4c and 5.
A selected set of N1-(4-chloro-9-ethylcarbazol-3-yl)amidrazones (7a–n) has been synthesized by reacting the respective hydrazonoyl chloride 5 derived from 3-amino-9-ethylcarbazole (3), with an appropriate sec-cyclic amine (6a–n) in ethanol in the presence of triethylamine. Unexpectedly, aromatic ring chlorination occurred at C-4 of 3 during its conversion to 6 as evidenced by analytical and spectral data and further confirmed by single crystal X-ray structure determination of the amidrazone 7n. Compounds 7a–n were tested for their in vitro antibacterial activity. Among the tested bacterial strains, methicillin-resistant Staphylococcus aureus was the most susceptible to 7f and Bacillus cereus to 7b both with a minimum inhibitory concentration value of 1.56 µg mL−1. Compounds 7c, 7f, and 7h could be useful as lead structures for further development of new antibacterial agents against Gram-positive and Gram-negative pathogens.