Piperidines+ 33
Pyridines+ 31
Piperazines+ 25
Pyrimidines+ 19
Pyrrolidines+ 15
Furans+ 11
Pyrans+ 11
Thiophenes+ 10
Triazines+ 9
Azoles+ 8
Azepines+ 7
Thiazines+ 6
Lactams+ 4
Pyridazines+ 4
Oxazines+ 3
Azirines+ 2
Azocines+ 2
Dioxins+ 2
Dioxoles+ 2
Pyrazines+ 2
Thiepins+ 2
Azetines+ 1
Oxathiins+ 1
Oxepins+ 1
Oxocins