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Treatment of 1-hydroxy-2,3-dihydro-1H-pyrazolo[1,2-a]pyridazine-5,8-diones and -1H-pyrazolo[1,2-b]phthalazine-5,10-diones with hydrazides produces corresponding acylhydrazino derivatives. In this work, ten new hydrazino derivatives were synthesized, and their properties were studied by 1 H and 13 C NMR spectroscopy. These compounds exhibited several types of structural variation, including ring-chain tautomerism, cis-trans isomerism with respect to the substituents in the pyrazole ring, and (E)/(Z) rotamerism with respect to the nitrogen−carbon hydrazide bond with partial double-

Pyrazine derivatives Pyrazine derivatives R 0550Synthesis and Pharmacological Activity of 1-Hydroxy-, 1-Amino-and 1-Hydrazino-2,3-dihydro-1H-pyrazolo[1,2-a]pyridazine-5,8-diones and -2,3-dihydro-1H-pyrazolo[1,2-b]phthalazine-5,10-diones. -A variety of functionalized fused pyrazine derivatives [cf. (III), (V), (VII)] are synthesized and evaluated for their pharmacological properties. Among these compounds, derivatives (IIId), and (Vb)-(Vd) are the most interesting ones due to their antiinflammatory, analgesic, antihypoxic and antipyretic properties. -(AL'-ASSAR, F.; ZELENIN, K. N.; LESIOVSKAYA, E. E.; BEZHAN, I. P.; CHAKCHIR, B. A.; Khim.-Farm. Zh. 36 (2002) 11, 23-27; St. Peterburgskaya khim.-farm. akad., St. Petersburg 197376, Russia; Russ.) -Koehler 16-162

1‐Hydroxy‐2,3‐dihydro‐1H‐pyrazolo[1,2‐a]pyridazine‐5,8diones and 1‐hydroxy‐ and 1‐amino‐2,3‐dihydro‐1H‐pyrazolo[1,2‐b]phthalazine‐5,10‐diones were synthesized and their structures studied by NMR and MS methods. All compounds exist in similar cyclic forms in solution, except for 1hydroxy‐1‐methyl‐2,3‐dihydro‐1H‐pyrazolo[1,2‐a]pyridazine‐5,8‐dione, which displays ring‐chain tautomerism in CDCl3 solution. The corresponding 3‐methyl‐substituted derivatives exhibit a typical cis/trans isomerism as a result of latent ring‐chain‐ring tautomerism. The structures of stereoisomers concluded from NMR results were additionally confirmed by density functional calculations. Mass spectrometric results indicate open‐chain structures in the gas phase for the molecular ions of the 1‐hydroxy derivatives and cyclic structures for 1‐amino derivatives. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)