Pyrimido tetrazines

Reports concerning bridgehead nitrogen bicyclic systems containing four extra heteroatoms (3 1) are rare <1996CHEC-II(8)729>. Only four such ring systems, 1-4, have been reported previously. Related ring systems reported in the last decade are l,2-dihydropyrimido[l,2- ]-l,2,4,5-tetrazin-6-ones 5, 67/-[l,2,4,5]tetrazino[3,2- ] quinazolin-6-ones 6, thioxotetrazinoquinazoline 7, and pyrimido[l,2- ]-l,2,4,5-tetrazin-6-ones 8. 

The 13C NMR spectrum (75 MHz) is available only for pyrimido[ 1,2-3]-l,2,4,5-tetrazin-6-ones 8, which showed the characteristic carbonyl carbon resonance at 8 156.8ppm <2004JCM399>. 

Refluxing a mixture of hydrazonoyl halides 13 and heterocyclic thiones 14 in ethanol in the presence of triethylamine resulted in the formation of 3-arylazo-l,4-dihydro-l,7-disubstituted-pyrimido[l,2,-3]-l,2,4,5-tetrazin-6-ones 8. The reaction starts with the initial formation of the hydrazidine derivatives 15, which in turn undergo cyclization with the elimination of thiolate to give the desired product 8 (Scheme 1)<2004JCM399>. 

Many of these heterocyclic systems are of biological importance but detailed information regarding their biological activities is still lacking. Pyrimido[l,2- ]-l,2,4,5-tetrazin-6-ones 21 have been identified as potent inhibitors of the... 

Pyrimido[3, 2 4,5]thieno[3,2-rijpyrimidinoncs reacted with hydrazonoyl halides in dioxane and triethylamine to give the corresponding tetracyclic fused tetrazines <06JHC935>. 

Acid-catalyzed 1,2,4,5-tetrazine ring contraction of the pyrimido[l,2-h]l,2,4,5-tetrazines 116 led to the formation of the 8-amino-l,2,4-tria-... 

The synthesis and NMR study of benzo[l,2,3,4]tetrazine 1,3-dioxides have been described <02EJO2342>. A convenient one-pot synthesis and antimicrobial activity of pyrimido[l,2-6][l,2,4,5]tetrazines 68 bearing different substituents have been reported <02JHC45>. 

The synthesis and biological activity of pyrimido[l,2-i>]-l,2,4,5-tetrazin-6-ones as HCMV protease inhibitors has been reported <03BMCL3483>. Novel 6-azapteridines from bifunctional... 

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