“…Once more, such pattern substitution relates to the different biological activities these two families of structures have been oriented towards. [36,76] In summary, the combinations of substituents apparently more widely explored in literature for both structures are a) In 14.08% of the 5,6-dihydropyrido[2,3-d]pyrimidin-7(8H)-ones (11): G 2 = nitrogen substituent, G 4 = oxygen substituent (in particular as a carbonyl group), R 5 = phenyl group, R 6 Thus, in the case of the structures 11 (C5-C6 single bond), 53.12% present at least a substituent at C5 and a CH2 at C6 (in most of them a carbon substituent [29,30] and, more precisely, a phenyl ring in one half of the structures [50,51]) while only 3.19% present a substituent at C6 and a CH2 at C5 (in this case most structures present a carbon substituent [52,53] which is a phenyl ring in also one half of them [31,42]). Finally, 20.86% of the structures do not present substituents at C5 or C6 [20,54].…”