The present invention discloses the novel coumarin derivative 7 9 dihydroxy 3 (4 5 7 trihydroxy 2 oxo 2ff chromene 3 yl ) 4H furo [3 2 c] chromen 4 one (1) its synthesis pharmaceutical composition preparation and use thereof. The pharmaceutical composition comprising : (1) 7 9 dihydroxy 3 (4 5 7 trihydroxy 2 oxo 2JFi chromene 3 yl ) 4H furo [3 2 c] chromen 4 one (1) as active pharmaceutical ingredient and (2) one or more pharmaceutical excipients required to yield final dosage forms suitable for therapeutic administration. The composition is safe and efficient therapeutic agent for viral diseases including the acquired immunodeficiency syndrome (AIDS).