Hadeel T Al-Sinjilawi et al.
Archiv der Pharmazie, 347(11), 861-872 (2014-09-16)
A series of substituted 4-oxopyrido[2,3-a]phenothiazine-3-carboxylic acids (6a-d) were prepared via cyclization of the corresponding ethyl 7-(arylthioxy)-8-nitro(or azido)-4-oxoquinoline-3-carboxylates (3a-d/4a-d), followed by hydrolysis of the resultant esters (5a-d). Among these tetracyclics, compound 6a with unsubstituted terminal benzo-ring D was the most active