How to interpret BRICS fragments I have a molecule with a SMILES string as given below.
smi='c1ccccc1OCCOC(=O)CC'

I want to obtain BRICS based fragments which I did as follows.
frag=BRICS.BRICSDecompose(Chem.MolFromSmiles('c1ccccc1OCCOC(=O)CC'))

I obtain the following fragments.
{'[1*]C(=O)CC', '[16*]c1ccccc1', '[3*]O[3*]', '[4*]CC[4*]'}

How to interpret [1*], [16*], [3*] ,[4*] ? What does these number with brackets and stars means with each fragment?
Cutting a molecule (expressed with SMILES strings) into fragments yields sub-structures.  Typically these fragments can't be considered as molecules for their open, non-bonding valencies.  Derived from SMILES, it is then the SMARTS notation which is used to represent them, or to search with this notation of sub-structures in databases, e.g. in bioinformatics.
Open Babel supports the display of SMARTS-encoded fragments with branching points marked by an asterisk. The phenyl group, [16*]c1ccccc1 thus is shown as:

Consequently, bidental fragments are represented with two asterisks, e.g., [4*]CC[4*]: