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SMILESTM
Simplified Molecular Input
Line Entry System
SMILES
TM as a simple yet comprehensive chemical language
in which molecules and reactions can be specified using ASCII characters
representing atom and bond symbols. SMILES
TM contains the same information
as is found in an extended connection table but with several advantages. A
SMILES
TM string is human understandable, very compact, and if canonicalized
represents a unique string that can be used as a universal identifier for
a specific chemical structure. In addition, a chemically correct and
comprehensible depiction can be made from any SMILES
TM string symbolizing
either a molecule or reaction.
SMILES
TM development was initiated by David Weininger in the late 1980s
using the concept of a
graph with
nodes as atoms
and
edges as bonds to represent a molecule. Parentheses are
used to indicate branching points and numeric labels designate ring
connection points. The basic SMILES
TM grammar also includes
as well as isotopic information, configuration about double bonds, and chirality
leading to what is known as isomeric SMILES
TM.
Some simple SMILES
TM examples:
Ethanol
CCO
Acetic acid
CC(=O)O
Cyclohexane
C1CCCCC1
Pyridine
c1cnccc1
Trans-2-butene
C/C=C/C
L-alanine
N[C@@H](C)C(=O)O
Sodium chloride
[Na+].[Cl-]
Displacement reaction
C=CCBr>>C=CCI
Since its inception, SMILES
TM has been modified and expanded by Daylight to include not only new features but two additional chemical languages:
SMARTS
®, an expansion of SMILES
TM allowing specification
of molecular patterns
and properties for substructure searching with varying levels of specificity,
and SMIRKS
®, a restricted version of reaction SMARTS
® involving changes in
atom-bond patterns that define generic reactions.