How to use SMARTS expressions in a substructure search using "babel" commands?

You can use SMARTS expressions in the "-s ..." option in "babel" commands to filter molecules that match given SMARTS expressions.

Here are some examples:

# C, C and O connected with single bonds
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s C-C-O
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# same as above with single bonds omitted
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s CCO
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# same as above atom expression with optional brackets added 
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s C[C]O
c1cc(ccc1CC(C(=O)O)N)O
1 molecule converted

# double conditions on the middle atom
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s C[CH0]O
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# same as above with implicit & included
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s 'C[C&H0]O'
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# bond expression used
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s 'C-,=O'
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# same as above, but in a native way
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s 'C!#O'
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# bad bond expression, no bond can be both single and double. 
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s 'C-=O'
0 molecules converted

# poor bond expression, a single bond is also an any bond. 
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s 'C-~O'
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# matching aromatic C and connected with 1 H
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s '[c;H1]'
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# matching aromatic C and connected with 0 H
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s '[c;H0]'
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

# nested SMARTS expressions
fyicenter$ obabel "-:c1cc(ccc1CC(C(=O)O)N)O" -o smiles -s '[C;H0]-,=[$([O;H1]),$([O;H0])]'
c1cc(ccc1CC(C(=O)O)N)O  
1 molecule converted

You can validate the above matching result by looking at the tyrosine molecule structure below:

⇒ Similarity Search with Open Babel

⇐ What Are SMARTS Expressions

⇑ Substructure Search with Open Babel

⇑⇑ Open Babel Tutorials