Extended SMILES, SMARTS

Code name: cxsmiles,cxsmarts

ChemAxon Extended SMILES/SMARTS is used for storing special features of the molecules after the SMILES string. Any information can be stored after the SMILES string if it is separated by space or tab characters as the SMILES parsers ignore them or use them as comment. The extended features is stored in the following format:
SMILES_String |<feature1>,<feature2>,...|
The extended feature description is economic. If some feature is missing in the molecule, then the corresponding special characters are not written. (Eg: If the atoms of the molecule has no alias strings at all, no "$" and ";" characters are written.) Moreover, if no feature of the molecule to be written, the extended feature field is omitted.

In extended smiles export the following additional features are exported:

• Molecule absolute stereoconfiguration

  The relative stereoconfiguration is stored as "r". The absolute stereoconfiguration is the default, which is not marked. (Absolute stereoconfiguration known also as "Chiral flag" in MDL molfiles.)

• Enhanced stereochemical representation

  The following stereochemical group types are stored:

  • Absolute stereo group type.
    a:<atomnumber>,<atomnumber>...
  • OR stereo group type.
    o<group>:<atomnumber>,< atomnumber>...
  • AND stereo group type.
    &<group>:<atomnumber>,< atomnumber>...
• Atom labels

  Atom labels are written between "$" characters each label is separated by ";" characters.

• Single "Up or Down" (Wiggly) bonds

  Atom indexes relating to wiggly bonds are written after "w:" followed by the wiggly bond index and separated by commas.

• CIS, TRANS, UNSPEC bond info for double bonds in rings

  Bond indexes of the double bonds in SSSR are written.
  The bond stereo information is generated as the following: the double bond has the representation a1-a2=a3-a4, where
  

  • a1 is the smallest atom index of the generated smiles connected to a2
  • a2 is the double bond smaller atom index in the generated smiles
  • a3 is the double bond larger atom index in the generated smiles
  • a4 is the smallest atom index of the generated smiles connected to a3
  The CIS double bond indexes are written after "c:",
  the TRANS double bond indexes are written after "t:",
  the double bond indexes with UNSPEC flag are written after "u:".
• Fragment level grouping of reactant, agent and product fragments Grouped fragment indexes are written after "f:" in the following format:
  
  • Connected groups are separated by ",".
  • A connected group is a "." separated list of fragment indices.
  
  Example: "f:0.1,5.6"

Import options

See SMILES import options

Export options

Export options can be specified in the format string. The format descriptor and the options are separated by a colon.
If no ChemAxon Extended SMILES/SMARTS specific export option (detailed below) is given, all export option is used.
Examples: "cxmiles:le" writes only atom labels and wiggly bond indexes,
"cxmiles:" writes all features (absolute stereoconfiguration, enhanced stereo features, atom labels, wiggly bond indexes, ring stereo bond info and reaction fragment level grouping).

e	Write relative stereo configuration and enhanced stereo features.
l	Write atom aliases.
w	Write wiggly bond indexes.
d	Write CIS, TRANS bond indexes.
f	Reaction fragment level grouping.

See also SMILES export options