| Summary: | Substituted-6-methyl-1-thioxo-1,2-dihydro-3<i>H</i>-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-ones (<b>5a</b>,<b>b</b>) were synthesized from condensation of visnagenone (<b>2a</b>) or khellinone (<b>2b</b>) with 6-amino-thiouracil (<b>3</b>) in dimethylformamide or refluxing of (<b>4a</b>) or (<b>4b</b>) in dimethylformamide. Hence, compounds (<b>5a</b>,<b>b</b>) were used as the starting materials for preparing many new heterocyclic compounds such as; furo[3,2-g]pyrimido[1,6-a]quinazoline (<b>6a</b>,<b>b</b>), furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazolinone (<b>7a</b>,<b>b</b>), substituted-benzylidene-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione (<b>8a</b>⁻<b>f</b>), 3-oxo-furo[3,2-g]pyrimido[1,6-a]quinazoline-pentane-2,4-dione (<b>9a</b>,<b>b</b>), 1-(pyrazole)-furo[3,2-g]pyrimido[1,6-a]quinazolinone (<b>10a</b>,<b>b</b>), 2-(oxo or thioxo)-pyrimidine-furo[3,2-g]pyrimido[1,6-a]quinazolinone (<b>11a</b>⁻<b>d</b>), 1-(methylthio)-furo[3,2-g]pyrimido[1,6-a]quinazolinone (<b>12a</b>,<b>b</b>), 1-(methyl-sulfonyl)-furo[3,2-g]pyrimido[1,6-a]quinazolinone (<b>13a</b>,<b>b</b>) and 6-methyl-1-((piperazine) or morpholino)-3<i>H</i>-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (<b>14a</b>⁻<b>d</b>). The structures of the prepared compounds were elucidated on the basis of spectral data (IR, <sup>1</sup>H-NMR, <sup>13</sup>C-NMR, MS) and elemental analysis. Antimicrobial activity was evaluated for the synthesized compounds against Gram-positive, Gram-negative bacteria and fungi. The new compounds, furothiazolo pyrimido quinazolines <b>8a</b>⁻<b>f</b> and <b>11a</b>⁻<b>d</b> displayed results excellent for growth inhibition of bacteria and fungi.
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