[Rdkit-discuss] AllChem.ReplaceSubstructs question

[Markus M. <me...@gm...>]

Hello:
I am puzzled by the output from ReplaceSubstructs as it can produce two
fragments.
So I went and tried the examples in the manual and I observed this:
The example in the intro manual with the recursive smarts pattern works as
expected.
repl = Chem.MolFromSmiles('OC')
patt = Chem.MolFromSmarts('[$(NC(=O))]')
m = Chem.MolFromSmiles('CC(=O)N')
rms = AllChem.ReplaceSubstructs(m,patt,repl)
One expected product is formed.

The example form the ReplaceSubstructs manual produces two solutions.
I have used the following commands:
from rdkit import Chem
from rdkit.Chem import AllChem

#ReplaceSubstructs(‘CCOC’,’OC’,’NC’) -> (‘CCNC’,)
repl = Chem.MolFromSmiles('NC')
patt = Chem.MolFromSmarts('OC')
m = Chem.MolFromSmiles('CCOC')
rms = AllChem.ReplaceSubstructs(m,patt,repl)

for rm in rms:
   print(CHem.MolToSmiles(rm))

output is: C.CNC and CCNC

Why is the first result produced?
I checked the mailing list and could find this older threat
https://sourceforge.net/p/rdkit/mailman/message/28777648/.
But the answer to the related question is missing.

rdkit version is 2020.03.1dev1

Best wishes,
Markus