Substitution at the 7-position of the chromen-4-one pharmacophore of 8-(dibenzo [b, d] thiophen-4-yl)-2-morpholino-4H-chromen-4-one NU7441, a potent and selective DNA- dependent protein kinase (DNA-PK) inhibitor, with allyl, n-propyl or methyl enabled the resolution by chiral HPLC of atropisomers. Biological evaluation against DNA-PK of each pair of atropisomers showed a marked difference in potency, with biological activity ...