SMARTS Examples

Table of Contents

1. Introduction

2. Functional Groups by Element

C

alkane

Alkyl Carbon

[CX4]

alkene (-ene)

Allenic Carbon

[$([CX2](=C)=C)]

Vinylic Carbon

[$([CX3]=[CX3])]

Ethenyl carbon

alkyne (-yne)

Acetylenic Carbon

[$([CX2]#C)]

arene (Ar , aryl-, aromatic hydrocarbons)

Arene

c

C & O

carbonyl

Carbonyl group. Low specificity

[CX3]=[OX1]

Hits carboxylic acid, ester, ketone, aldehyde, carbonic acid/ester,anhydride, carbamic acid/ester, acyl halide, amide.

Carbonyl group

[$([CX3]=[OX1]),$([CX3+]-[OX1-])]

Hits either resonance structure

Carbonyl with Carbon

[CX3](=[OX1])C

Hits aldehyde, ketone, carboxylic acid (except formic), anhydride (except formic), acyl halides (acid halides). Won't hit carbamic acid/ester, carbonic acid/ester.

Carbonyl with Nitrogen.

[OX1]=CN

Hits amide, carbamic acid/ester, poly peptide

Carbonyl with Oxygen.

[CX3](=[OX1])O

Hits ester, carboxylic acid, carbonic acid or ester, carbamic acid or ester, anhydride Won't hit aldehyde or ketone.

Acyl Halide

[CX3](=[OX1])[F,Cl,Br,I]

acid halide, -oyl halide

Aldehyde

[CX3H1](=O)[#6]

-al

Anhydride

[CX3](=[OX1])[OX2][CX3](=[OX1])

Amide

[NX3][CX3](=[OX1])[#6]

-amide

Amidinium

[NX3][CX3]=[NX3+]

Carbamate.

[NX3,NX4+][CX3](=[OX1])[OX2,OX1-]

Hits carbamic esters, acids, and zwitterions

Carbamic ester

[NX3][CX3](=[OX1])[OX2H0]

Carbamic acid.

[NX3,NX4+][CX3](=[OX1])[OX2H,OX1-]

Hits carbamic acids and zwitterions.

Carboxylate Ion.

[CX3](=O)[O-]

Hits conjugate bases of carboxylic, carbamic, and carbonic acids.

Carbonic Acid or Carbonic Ester

[CX3](=[OX1])(O)O

Carbonic Acid, Carbonic Ester, or combination

Carbonic Acid or Carbonic Acid-Ester

[CX3](=[OX1])([OX2])[OX2H,OX1H0-1]

Hits acid and conjugate base. Won't hit carbonic acid diester

Carbonic Ester (carbonic acid diester)

C[OX2][CX3](=[OX1])[OX2]C

Won't hit carbonic acid or combination carbonic acid/ester

Carboxylic acid

[CX3](=O)[OX2H1]

-oic acid, COOH

Carboxylic acid or conjugate base.

[CX3](=O)[OX1H0-,OX2H1]

Cyanamide

[NX3][CX2]#[NX1]

Ester Also hits anhydrides

[#6][CX3](=O)[OX2H0][#6]

won't hit formic anhydride.

Ketone

[#6][CX3](=O)[#6]

-one

ether

Ether

[OD2]([#6])[#6]

H

hydrogen atoms

Hydrogen Atom

[H]

Hits SMILES that are hydrogen atoms: [H+] [2H] [H][H]

Not a Hydrogen Atom

[!#1]

Hits SMILES that are not hydrogen atoms.

Proton

[H+]

Hits positively charged hydrogen atoms: [H+]

hydrogen count

Mono-Hydrogenated Cation

[+H]

Hits atoms that have a positive charge and exactly one attached hydrogen: F[C+](F)[H]

Not Mono-Hydrogenated

[!H] or [!H1]

Hits atoms that don't have exactly one attached hydrogen.

N

amide see carbonyl

mine (-amino)

Primary or secondary amine, not amide.

[NX3;H2,H1;!$(NC=O)]

Not ammonium ion (N must be 3-connected), not ammonia (H count can't be 3). Primary or secondary is specified by N's H-count (H2 & H1 respectively). Also note that "&" (and) is the dafault opperator and is higher precedence that "," (or), which is higher precedence than ";" (and). Will hit cyanamides and thioamides

Enamine

[NX3][CX3]=[CX3]

Primary amine, not amide.

[NX3;H2;!$(NC=[!#6]);!$(NC#[!#6])][#6] Not amide (C not double bonded to a hetero-atom), not ammonium ion (N must be 3-connected), not ammonia (N's H-count can't be 3), not cyanamide (C not triple bonded to a hetero-atom)

Two primary or secondary amines

[NX3;H2,H1;!$(NC=O)].[NX3;H2,H1;!$(NC=O)]

Here we use the disconnection symbol (".") to match two separate unbonded identical patterns.

Enamine or Aniline Nitrogen

[NX3][$(C=C),$(cc)]

amino acids

Generic amino acid: low specificity.

[NX3,NX4+][CX4H]([*])[CX3](=[OX1])[O,N]

For use w/ non-standard a.a. search. hits pro but not gly. Hits acids and conjugate bases. Hits single a.a.s and specific residues w/in polypeptides (internal, or terminal).

Dipeptide group. generic amino acid: low specificity.

[NX3H2,NH3X4+][CX4H]([*])[CX3](=[OX1])[NX3,NX4+][CX4H]([*])[CX3](=[OX1])[OX2H,OX1-]

Won't hit pro or gly. Hits acids and conjugate bases.

Amino Acid

[$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H]([*])[CX3](=[OX1])[OX2H,OX1-,N]

Replace * w/ a specific a.a. side chain from the 18_standard_side_chains list to hit a specific standard a.a. Won't work with Proline or Glycine, they have their own SMARTS (see side chain list). Hits acids and conjugate bases. Hits single a.a.s and specific residues w/i n polypeptides (internal, or terminal). {e.g. usage: Alanine side chain is [CH3X4] . Search is [$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H]([ CH3X4])[CX3](=[OX1])[OX2H,OX1-,N]}

amino acid side chains

Alanine side chain

[CH3X4]

Arginine side chain.

[CH2X4][CH2X4][CH2X4][NHX3][CH0X3](=[NH2X3+,NHX2+0])[NH2X3]

Hits acid and conjugate base.

Aspargine side chain.

[CH2X4][CX3](=[OX1])[NX3H2]

Also hits Gln side chain when used alone.

Aspartate (or Aspartic acid) side chain.

[CH2X4][CX3](=[OX1])[OH0-,OH]

Hits acid and conjugate base. Also hits Glu side chain when used alone.

Cysteine side chain.

[CH2X4][SX2H,SX1H0-]

Hits acid and conjugate base

Glutamate (or Glutamic acid) side chain.

[CH2X4][CH2X4][CX3](=[OX1])[OH0-,OH]

Hits acid and conjugate base.

Glycine

[$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H2][CX3](=[OX1])[OX2H,OX1-,N])]

Histidine side chain.

[CH2X4][#6X3]1:[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:[#6X3H]:
[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:[#6X3H]1

Hits acid & conjugate base for either Nitrogen. Note that the Ns can be either ([(Cationic 3-connected with one H) or (Neutral 2-connected without any Hs)] where there is a second-neighbor who is [3-connected with one H]) or (3-connected with one H).

Isoleucine side chain

[CHX4]([CH3X4])[CH2X4][CH3X4]

Leucine side chain

[CH2X4][CHX4]([CH3X4])[CH3X4]

Lysine side chain.

[CH2X4][CH2X4][CH2X4][CH2X4][NX4+,NX3+0]

Acid and conjugate base

Methionine side chain

[CH2X4][CH2X4][SX2][CH3X4]

Phenylalanine side chain

[CH2X4][cX3]1[cX3H][cX3H][cX3H][cX3H][cX3H]1

Proline

[$([NX3H,NX4H2+]),$([NX3](C)(C)(C))]1[CX4H]([CH2][CH2][CH2]1)[CX3](=[OX1])[OX2H,OX1-,N]

Serine side chain

[CH2X4][OX2H]

Thioamide

[NX3][CX3]=[SX1]

Threonine side chain

[CHX4]([CH3X4])[OX2H]

Tryptophan side chain

[CH2X4][cX3]1[cX3H][nX3H][cX3]2[cX3H][cX3H][cX3H][cX3H][cX3]12

Tyrosine side chain.

[CH2X4][cX3]1[cX3H][cX3H][cX3]([OHX2,OH0X1-])[cX3H][cX3H]1

Acid and conjugate base

Valine side chain

[CHX4]([CH3X4])[CH3X4]

Alanine side chain

[CH3X4]

Arginine side chain.

[CH2X4][CH2X4][CH2X4][NHX3][CH0X3](=[NH2X3+,NHX2+0])[NH2X3]

Hits acid and conjugate base.

Aspargine side chain.

[CH2X4][CX3](=[OX1])[NX3H2]

Also hits Gln side chain when used alone.

Aspartate (or Aspartic acid) side chain.

[CH2X4][CX3](=[OX1])[OH0-,OH]

Hits acid and conjugate base. Also hits Glu side chain when used alone.

Cysteine side chain.

[CH2X4][SX2H,SX1H0-]

Hits acid and conjugate base

Glutamate (or Glutamic acid) side chain.

[CH2X4][CH2X4][CX3](=[OX1])[OH0-,OH]

Hits acid and conjugate base.

Glycine

N[CX4H2][CX3](=[OX1])[O,N]

Histidine side chain.

[CH2X4][#6X3]1:[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:[#6X3H]:
[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:[#6X3H]1

Hits acid & conjugate base for either Nitrogen. Note that the Ns can be either ([(Cationic 3-connected with one H) or (Neutral 2-connected without any Hs)] where there is a second-neighbor who is [3-connected

Isoleucine side chain

[CHX4]([CH3X4])[CH2X4][CH3X4]

Leucine side chain

[CH2X4][CHX4]([CH3X4])[CH3X4]

Lysine side chain.

[CH2X4][CH2X4][CH2X4][CH2X4][NX4+,NX3+0]

Acid and conjugate base

Methionine side chain

[CH2X4][CH2X4][SX2][CH3X4]

Phenylalanine side chain

[CH2X4][cX3]1[cX3H][cX3H][cX3H][cX3H][cX3H]1

Proline

N1[CX4H]([CH2][CH2][CH2]1)[CX3](=[OX1])[O,N]

Serine side chain

[CH2X4][OX2H]

Threonine side chain

[CHX4]([CH3X4])[OX2H]

Tryptophan side chain

[CH2X4][cX3]1[cX3H][nX3H][cX3]2[cX3H][cX3H][cX3H][cX3H][cX3]12

Tyrosine side chain.

[CH2X4][cX3]1[cX3H][cX3H][cX3]([OHX2,OH0X1-])[cX3H][cX3H]1

Acid and conjugate base

Valine side chain

[CHX4]([CH3X4])[CH3X4]

azide (-azido)

Azide group.

[$(*-[NX2-]-[NX2+]#[NX1]),$(*-[NX2]=[NX2+]=[NX1-])]

Hits any atom with an attached azide.

Azide ion.

[$([NX1-]=[NX2+]=[NX1-]),$([NX1]#[NX2+]-[NX1-2])]

Hits N in azide ion

azo

Nitrogen.

[#7]

Nitrogen in N-containing compound. aromatic or aliphatic. Most general interpretation of "azo"

Azo Nitrogen. Low specificity.

[NX2]=N

Hits diazene, azoxy and some diazo structures

Azo Nitrogen.diazene

[NX2]=[NX2]

(diaza alkene)

Azoxy Nitrogen.

[$([NX2]=[NX3+]([O-])[#6]),$([NX2]=[NX3+0](=[O])[#6])]

Diazo Nitrogen

[$([#6]=[N+]=[N-]),$([#6-]-[N+]#[N])]

Azole.

[$([nr5]:[nr5,or5,sr5]),$([nr5]:[cr5]:[nr5,or5,sr5])]

5 member aromatic heterocycle w/ 2double bonds. contains N & another non C (N,O,S) subclasses are furo-, thio-, pyrro- (replace CH o' furfuran, thiophene, pyrrol w/ N)

hydrazine

Hydrazine H2NNH2

[NX3][NX3]

hydrazone

Hydrazone C=NNH2

[NX3][NX2]=[*]

imine

Substituted imine

[CX3;$([C]([#6])[#6]),$([CH][#6])]=[NX2][#6]

Schiff base

Substituted or un-substituted imine

[$([CX3]([#6])[#6]),$([CX3H][#6])]=[$([NX2][#6]),$([NX2H])]

Iminium

[NX3+]=[CX3]

imide

Unsubstituted dicarboximide

[CX3](=[OX1])[NX3H][CX3](=[OX1])

Substituted dicarboximide

[CX3](=[OX1])[NX3H0]([#6])[CX3](=[OX1])

Dicarboxdiimide

[CX3](=[OX1])[NX3H0]([NX3H0]([CX3](=[OX1]))[CX3](=[OX1]))[CX3](=[OX1])

nitrate

Nitrate group

[$([NX3](=[OX1])(=[OX1])O),$([NX3+]([OX1-])(=[OX1])O)]

Also hits nitrate anion

Nitrate Anion

[$([OX1]=[NX3](=[OX1])[OX1-]),$([OX1]=[NX3+]([OX1-])[OX1-])]

nitrile

Nitrile

[NX1]#[CX2]

Isonitrile

[CX1-]#[NX2+]

nitro

Nitro group.

[$([NX3](=O)=O),$([NX3+](=O)[O-])][!#8] Hits both forms.

Two Nitro groups

[$([NX3](=O)=O),$([NX3+](=O)[O-])][!#8].[$([NX3](=O)=O),$([NX3+](=O)[O-])][!#8]

nitroso

Nitroso-group

[NX2]=[OX1]

n-oxide

N-Oxide

[$([#7+][OX1-]),$([#7v5]=[OX1]);!$([#7](~[O])~[O]);!$([#7]=[#7])]

Hits both forms. Won't hit azoxy, nitro, nitroso,or nitrate.

O

hydroxyl (includes alcohol, phenol)

Hydroxyl

[OX2H]

Hydroxyl in Alcohol

[#6][OX2H]

Hydroxyl in Carboxylic Acid

[OX2H][CX3]=[OX1]

Hydroxyl in H-O-P-

[OX2H]P

Enol

[OX2H][#6X3]=[#6]

Phenol

[OX2H][cX3]:[c]

Enol or Phenol

[OX2H][$(C=C),$(cc)]

Hydroxyl_acidic

[$([OH]-*=[!#6])]

An acidic hydroxyl is a hydroxyl bonded to an atom which is multiply bonded to a hetero atom, this includes carboxylic, sulphur, phosphorous, halogen and nitrogen oxyacids.

peroxide

Peroxide groups.

[OX2,OX1-][OX2,OX1-]

Also hits anions.

P

phosphoric compounds

Phosphoric_acid groups.

[$(P(=[OX1])([$([OX2H]),$([OX1-]),$([OX2]P)])([$([OX2H]),$([OX1-]),$([OX2]P)])[$([OX2H]),$([OX1-]),$([OX2]P)]),$([P+]([OX1-])([$([OX2H]),$([OX1-]),$([OX2]P)])([$([OX2H]),$([OX1-]),$([OX2]P)])[$([OX2H]),$([OX1-]),$([OX2]P)])]

Hits both depiction forms. Hits orthophosphoric acid and polyphosphoric acid anhydrides. Doesn't hit monophosphoric acid anhydride esters (including acidic mono- & di- esters) but will hit some polyphosphoric acid anhydride esters (mono- esters on pyrophosphoric acid and longer, di- esters on linear triphosphoric acid and longer).

Phosphoric_ester groups.

[$(P(=[OX1])([OX2][#6])([$([OX2H]),$([OX1-]),$([OX2][#6])])[$([OX2H]),$([OX1-]),$([OX2][#6]),$([OX2]P)]),$([P+]([OX1-])([OX2][#6])([$([OX2H]),$([OX1-]),$([OX2][#6])])[$([OX2H]),$([OX1-]),$([OX2][#6]),$([OX2]P)])]

Hits both depiction forms. Doesn't hit non-ester phosphoric_acid groups.

S

thio groups ( thio-, thi-, sulpho-, mercapto- )

Carbo-Thiocarboxylate

[S-][CX3](=S)[#6]

Carbo-Thioester

S([#6])[CX3](=O)[#6]

Thio analog of carbonyl

[#6X3](=[SX1])([!N])[!N]

Where S replaces O. Not a thioamide.

Thiol, Sulfide or Disulfide Sulfur

[SX2]

Thiol

[#16X2H]

Sulfur with at-least one hydrogen.

[#16!H0]

Thioamide

[NX3][CX3]=[SX1]

sulfide

Sulfide

[#16X2H0]

-alkylthio Won't hit thiols. Hits disulfides.

Mono-sulfide

[#16X2H0][!#16]

alkylthio- or alkoxy- Won't hit thiols. Won't hit disulfides.

Di-sulfide

[#16X2H0][#16X2H0]

Won't hit thiols. Won't hit mono-sulfides.

Two Sulfides

[#16X2H0][!#16].[#16X2H0][!#16]

Won't hit thiols. Won't hit mono-sulfides. Won't hit disulfides.

sulfinate

Sulfinate

[$([#16X3](=[OX1])[OX2H0]),$([#16X3+]([OX1-])[OX2H0])]

Won't hit Sulfinic Acid. Hits Both Depiction Forms.

Sulfinic Acid

[$([#16X3](=[OX1])[OX2H,OX1H0-]),$([#16X3+]([OX1-])[OX2H,OX1H0-])]

Won't hit substituted Sulfinates. Hits Both Depiction Forms. Hits acid and conjugate base (sulfinate).

sulfone

Sulfone. Low specificity.

[$([#16X4](=[OX1])=[OX1]),$([#16X4+2]([OX1-])[OX1-])]

Hits all sulfones, including heteroatom-substituted sulfones: sulfonic acid, sulfonate, sulfuric acid mono- & di- esters, sulfamic acid, sulfamate, sulfonamide... Hits Both Depiction Forms.

Sulfone. High specificity.

[$([#16X4](=[OX1])(=[OX1])([#6])[#6]),$([#16X4+2]([OX1-])([OX1-])([#6])[#6])]

Only hits carbo- sulfones (Won't hit herteroatom-substituted molecules). Hits Both Depiction Forms.

Sulfonic acid. High specificity.

[$([#16X4](=[OX1])(=[OX1])([#6])[OX2H,OX1H0-]),$([#16X4+2]([OX1-])([OX1-])([#6])[OX2H,OX1H0-])]

Only hits carbo- sulfonic acids (Won't hit herteroatom-substituted molecules). Hits acid and conjugate base. Hits Both Depiction Forms. Hits Arene sulfonic acids.

Sulfonate

[$([#16X4](=[OX1])(=[OX1])([#6])[OX2H0]),$([#16X4+2]([OX1-])([OX1-])([#6])[OX2H0])]

(sulfonic ester) Only hits carbon-substituted sulfur (Oxygen may be herteroatom-substituted). Hits Both Depiction Forms.

Sulfonamide.

[$([#16X4]([NX3])(=[OX1])(=[OX1])[#6]),$([#16X4+2]([NX3])([OX1-])([OX1-])[#6])]

Only hits carbo- sulfonamide. Hits Both Depiction Forms.

Carbo-azosulfone

[SX4](C)(C)(=O)=N

Partial N-Analog of Sulfone

Sulfonamide

[$([SX4](=[OX1])(=[OX1])([!O])[NX3]),$([SX4+2]([OX1-])([OX1-])([!O])[NX3])]

(sulf drugs) Won't hit sulfamic acid or sulfamate. Hits Both Depiction Forms.

sulfoxide

Sulfoxide Low specificity.

[$([#16X3]=[OX1]),$([#16X3+][OX1-])]

( sulfinyl, thionyl ) Analog of carbonyl where S replaces C. Hits all sulfoxides, including heteroatom-substituted sulfoxides, dialkylsulfoxides carbo-sulfoxides, sulfinate, sulfinic acids... Hits Both Depiction Forms. Won't hit sulfones.

Sulfoxide High specificity

[$([#16X3](=[OX1])([#6])[#6]),$([#16X3+]([OX1-])([#6])[#6])]

(sulfinyl , thionyl) Analog of carbonyl where S replaces C. Only hits carbo-sulfoxides (Won't hit herteroatom-substituted molecules). Hits Both Depiction Forms. Won't hit sulfones.

sulfate

Sulfate

[$([#16X4](=[OX1])(=[OX1])([OX2H,OX1H0-])[OX2][#6]),$([#16X4+2]([OX1-])([OX1-])([OX2H,OX1H0-])[OX2][#6])]

(sulfuric acid monoester) Only hits when oxygen is carbon-substituted. Hits acid and conjugate base. Hits Both Depiction Forms.

Sulfuric acid ester (sulfate ester) Low specificity.

[$([SX4](=O)(=O)(O)O),$([SX4+2]([O-])([O-])(O)O)]

Hits sulfuric acid, sulfuric acid monoesters (sulfuric acids) and diesters (sulfates). Hits acid and conjugate base. Hits Both Depiction Forms.

Sulfuric Acid Diester.

[$([#16X4](=[OX1])(=[OX1])([OX2][#6])[OX2][#6]),$([#16X4](=[OX1])(=[OX1])([OX2][#6])[OX2][#6])]

Only hits when oxygen is carbon-substituted. Hits Both Depiction Forms.

sulfamate

Sulfamate.

[$([#16X4]([NX3])(=[OX1])(=[OX1])[OX2][#6]),$([#16X4+2]([NX3])([OX1-])([OX1-])[OX2][#6])]

Only hits when oxygen is carbon-substituted. Hits Both Depiction Forms.

Sulfamic Acid.

[$([#16X4]([NX3])(=[OX1])(=[OX1])[OX2H,OX1H0-]),$([#16X4+2]([NX3])([OX1-])([OX1-])[OX2H,OX1H0-])]

Hits acid and conjugate base. Hits Both Depiction Forms.

sulfene

Sulfenic acid.

[#16X2][OX2H,OX1H0-]

Hits acid and conjugate base.

Sulfenate.

[#16X2][OX2H0]

X

halide (-halo -fluoro -chloro -bromo -iodo)

Any carbon attached to any halogen

[#6][F,Cl,Br,I]

Halogen

[F,Cl,Br,I]

Three_halides groups

[F,Cl,Br,I].[F,Cl,Br,I].[F,Cl,Br,I]

Hits SMILES that have three halides.

acyl halide

Acyl Halide

[CX3](=[OX1])[F,Cl,Br,I]

(acid halide, -oyl halide)

3. Gross Structual Features

Chirality

Specified chiral carbon.

[$([#6X4@](*)(*)(*)*),$([#6X4@H](*)(*)*)]

Matches carbons whose chirality is specified (clockwise or anticlockwise) Will not match molecules whose chirality is unspecified b ut that could otherwise be considered chiral. Also,therefore won't match molecules that would be chiral due to an implicit connection (i.e.i mplicit H).

"No-conflict" chiral match

C[C@?](F)(Cl)Br

Will match molecules with chiralities as specified or unspecified.

"No-conflict" chiral match where an H is present

C[C@?H](Cl)Br

Will match molecules with chiralities as specified or unspecified.

Orbital Configuration

sp2 cationic carbon

[$([cX2+](:*):*)]

Aromatic cationic sp2 carbon with a free electron in a non-bonding sp2 hybrid orbital

Aromatic sp2 carbon.

[$([cX3](:*):*),$([cX2+](:*):*)]

The first recursive SMARTS matches carbons that are three-connected, the second case matches two-connected carbons (i.e cations with a free electron in a non-bonding sp2 hybrid orbital)

Any sp2 carbon.

[$([cX3](:*):*),$([cX2+](:*):*),$([CX3]=*),$([CX2+]=*)]

The first recursive SMARTS matches carbons that are three-connected and aromatic. The second case matches two-connected aromatic ca rbons (i.e cations with a free electron in a non-bonding sp2 hybrid orbital). The third case matches three-connected non-aromatic carbons ( alkenes). The fourth case matches non-aromatic cationic alkene carbons.

Any sp2 nitrogen.

[$([nX3](:*):*),$([nX2](:*):*),$([#7X2]=*),$([NX3](=*)=*),$([#7X3+](-*)=*),$([#7X3+H]=*)]

Can be aromatic 3-connected with 2 aromatic bonds (eg pyrrole,Pyridine-N-oxide), aromatic 2-connected with 2 aromatic bonds (and a free pair of electrons in a nonbonding orbital, e.g.Pyridine), either aromatic or non-aromatic 2-connected with a double bond (and a free pair of electrons in a nonbonding orbital, e.g. C=N ), non aromatic 3-connected with 2 double bonds (e.g. a nitro group; this form does not exist in reality, SMILES can represent the charge-separated resonance structures as a single uncharged structure), either aromatic or non-aromatic 3-connected cation w/ 1 single bond and 1 double bond (e.g. a nitro group, here the individual charge-separated resonance structures are specified), either aromatic or non-aromatic 3-connected hydrogenated cation with a double bond (as the previous case but R is hydrogen), rspectively.

Explicit Hydrogen on sp2-Nitrogen

[$([#1X1][$([nX3](:*):*),$([nX2](:*):*),$([#7X2]=*),$([NX3](=*)=*),$([#7X3+](-*)=*),$([#7X3+H]=*)])]

(H must be an isotope or ion)

sp3 nitrogen

[$([NX4+]),$([NX3]);!$(*=*)&!$(*:*)]

One atom that is (a 4-connected N cation or a 3-connected N) and is not double bonded and is not aromatically bonded.

Explicit Hydrogen on an sp3 N.

[$([#1X1][$([NX4+]),$([NX3]);!$(*=*)&!$(*:*)])]

One atom that is a 1-connected H that is bonded to an sp3 N. (H must be an isotope or ion)

sp2 N in N-Oxide

[$([$([NX3]=O),$([NX3+][O-])])]

sp3 N in N-Oxide Exclusive:

[$([$([NX4]=O),$([NX4+][O-])])]

Only hits if O is explicitly present. Won't hit if * is in SMILES in place of O.

sp3 N in N-Oxide Inclusive:

[$([$([NX4]=O),$([NX4+][O-,#0])])]

Hits if O could be present. Hits if * if used in place of O in smiles.

Connectivity

Quaternary Nitrogen

[$([NX4+]),$([NX4]=*)]

Hits non-aromatic Ns.

Tricoordinate S double bonded to N.

[$([SX3]=N)]

S double-bonded to Carbon

[$([SX1]=[#6])]

Hits terminal (1-connected S)

Triply bonded N

[$([NX1]#*)]

Divalent Oxygen

[$([OX2])]

Chains & Branching

Unbranched_alkane groups.

[R0;D2][R0;D2][R0;D2][R0;D2]

Only hits alkanes (single-bond chains). Only hits chains of at-least 4 members. All non-(implicit-hydrogen) atoms count as branches (e.g. halide substituted chains count as branched).

Unbranched_chain groups.

[R0;D2]~[R0;D2]~[R0;D2]~[R0;D2]

Hits any bond (single, double, triple). Only hits chains of at-least 4 members. All non-(implicit-hydrogen) atoms count as branches (e.g. halide substituted chains count as branched).

Long_chain groups.

[AR0]~[AR0]~[AR0]~[AR0]~[AR0]~[AR0]~[AR0]~[AR0]

Aliphatic chains at-least 8 members long.

Atom_fragment

[!$([#6+0]);!$(C(F)(F)F);!$(c(:[!c]):[!c])!$([#6]=,#[!#6])]

(CLOGP definition) A fragment atom is a not an isolating carbon

Carbon_isolating

[$([#6+0]);!$(C(F)(F)F);!$(c(:[!c]):[!c])!$([#6]=,#[!#6])]

This definition is based on that in CLOGP, so it is a charge-neutral carbon, which is not a CF3 or an aromatic C between two aromati c hetero atoms eg in tetrazole, it is not multiply bonded to a hetero atom.

Terminal S bonded to P

[$([SX1]~P)]

Nitrogen on -N-C=N-

[$([NX3]C=N)]

Nitrogen on -N-N=C-

[$([NX3]N=C)]

Nitrogen on -N-N=N-

[$([NX3]N=N)]

Oxygen in -O-C=N-

[$([OX2]C=N)]

Rotation

Rotatable bond

[!$(*#*)&!D1]-!@[!$(*#*)&!D1]

An atom which is not triply bonded and not one-connected i.e.terminal connected by a single non-ring bond to and equivalent atom. Note that logical operators can be applied to bonds ("-&!@"). Here, the overall SMARTS consists of two atoms and one bond. The bond is "site and not ring". *#* any atom triple bonded to any atom. By enclosing this SMARTS in parentheses and preceding with $, this enables us to use $(*#*) to write a recursive SMARTS using that string as an atom primitive. The purpose is to avoid bonds such as c1ccccc1-C#C which wo be considered rotatable without this specification.

Cyclic Features

Bicyclic

[$([*R2]([*R])([*R])([*R]))].[$([*R2]([*R])([*R])([*R]))]

Bicyclic compounds have 2 bridgehead atoms with 3 arms connecting the bridgehead atoms.

Ortho

*-!:aa-!:*

Ortho-substituted ring

Meta

*-!:aaa-!:*

Meta-substituted ring

Para

*-!:aaaa-!:*

Para-substituted ring

Acylic-bonds

*!@*

Single bond and not in a ring

*-!@*

Non-ring atom

[R0] or [!R]

Macrocycle groups.

[r;!r3;!r4;!r5;!r6;!r7]

S in aromatic 5-ring with lone pair

[sX2r5]

Aromatic 5-Ring O with Lone Pair

[oX2r5]

N in 5-sided aromatic ring

[nX2r5]

Spiro-ring center

[X4;R2;r4,r5,r6](@[r4,r5,r6])(@[r4,r5,r6])(@[r4,r5,r6])@[r4,r5,r6]rings size 4-6

N in 5-ring arom

[$([nX2r5]:[a-]),$([nX2r5]:[a]:[a-])] anion

CIS or TRANS double bond in a ring

*/,\[R]=;@[R]/,\*

An isomeric SMARTS consisting of four atoms and three bonds.

CIS or TRANS double or aromatic bond in a ring

*/,\[R]=,:;@[R]/,\*

Unfused benzene ring

[cR1]1[cR1][cR1][cR1][cR1][cR1]1

To find a benzene ring which is not fused, we write a SMARTS of 6 aromatic carbons in a ring where each atom is only in one ring:

Multiple non-fused benzene rings

[cR1]1[cR1][cR1][cR1][cR1][cR1]1.[cR1]1[cR1][cR1][cR1][cR1][cR1]1

Fused benzene rings

c12ccccc1cccc2

4. Meta-SMARTS

Amino Acids

Generic amino acid: low specificity.

[NX3,NX4+][CX4H]([*])[CX3](=[OX1])[O,N]

For use w/ non-standard a.a. search. hits pro but not gly. Hits acids and conjugate bases. Hits single a.a.s and specific residues w/in polypeptides (internal, or terminal).

A.A. Template for 20 standard a.a.s

[$([$([NX3H,NX4H2+]),$([NX3](C)(C)(C))]1[CX4H]([CH2][CH2][CH2]1)[CX3](=[OX1])[OX2H,OX1-,N]),
$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H2][CX3](=[OX1])[OX2H,OX1-,N]),$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H]([*])[CX3](=[OX1])[OX2H,OX1-,N])]

Pro, Gly, Other. Replace * w/ the entire 18_standard_side_chains list to get "any standard a.a." Hits acids and conjugate bases. Hits single a.a.s and specific residues w/in polypeptides (internal, or terminal).

Proline

[$([NX3H,NX4H2+]),$([NX3](C)(C)(C))]1[CX4H]([CH2][CH2][CH2]1)[CX3](=[OX1])[OX2H,OX1-,N]

Glycine

[$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H2][CX3](=[OX1])[OX2H,OX1-,N])]

Other a.a.

[$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H]([*])[CX3](=[OX1])[OX2H,OX1-,N]

Replace * w/ a specific a.a. side chain from the 18_standard_side_chains list to hit a specific standard a.a. Won't work with Proline or Glycine, they have their own SMARTS (see side chain list). Hits acids and conjugate bases. Hits single a.a.s and specific residues w/i polypeptides (internal, or terminal).
    Example usage:
    Alanine side chain is [CH3X4]
    Alanine Search is [$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H]([CH3X4])[CX3](=[OX1])[OX2H,OX1-,N]

18_standard_aa_side_chains.

([$([CH3X4]),$([CH2X4][CH2X4][CH2X4][NHX3][CH0X3](=[NH2X3+,NHX2+0])[NH2X3]),
$([CH2X4][CX3](=[OX1])[NX3H2]),$([CH2X4][CX3](=[OX1])[OH0-,OH]),
$([CH2X4][SX2H,SX1H0-]),$([CH2X4][CH2X4][CX3](=[OX1])[OH0-,OH]),
$([CH2X4][#6X3]1:[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:
[#6X3H]:[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:[#6X3H]1),
$([CHX4]([CH3X4])[CH2X4][CH3X4]),$([CH2X4][CHX4]([CH3X4])[CH3X4]),
$([CH2X4][CH2X4][CH2X4][CH2X4][NX4+,NX3+0]),$([CH2X4][CH2X4][SX2][CH3X4]),
$([CH2X4][cX3]1[cX3H][cX3H][cX3H][cX3H][cX3H]1),$([CH2X4][OX2H]),
$([CHX4]([CH3X4])[OX2H]),$([CH2X4][cX3]1[cX3H][nX3H][cX3]2[cX3H][cX3H][cX3H][cX3H][cX3]12),
$([CH2X4][cX3]1[cX3H][cX3H][cX3]([OHX2,OH0X1-])[cX3H][cX3H]1),$([CHX4]([CH3X4])[CH3X4])])

Can be any of the standard 18 (Pro & Gly are treated separately) Hits acids and conjugate bases.

N in Any_standard_amino_acid.

[$([$([NX3H,NX4H2+]),$([NX3](C)(C)(C))]1[CX4H]([CH2][CH2][CH2]1)[CX3]
(=[OX1])[OX2H,OX1-,N]),$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H2][CX3]
(=[OX1])[OX2H,OX1-,N]),$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H]([$([CH3X4]),
$([CH2X4][CH2X4][CH2X4][NHX3][CH0X3](=[NH2X3+,NHX2+0])[NH2X3]),$
([CH2X4][CX3](=[OX1])[NX3H2]),$([CH2X4][CX3](=[OX1])[OH0-,OH]),
$([CH2X4][SX2H,SX1H0-]),$([CH2X4][CH2X4][CX3](=[OX1])[OH0-,OH]),
$([CH2X4][#6X3]1:[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:
[#6X3H]:[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:[#6X3H]1),
$([CHX4]([CH3X4])[CH2X4][CH3X4]),$([CH2X4][CHX4]([CH3X4])[CH3X4]),
$([CH2X4][CH2X4][CH2X4][CH2X4][NX4+,NX3+0]),$([CH2X4][CH2X4][SX2][CH3X4]),
$([CH2X4][cX3]1[cX3H][cX3H][cX3H][cX3H][cX3H]1),$([CH2X4][OX2H]),
$([CHX4]([CH3X4])[OX2H]),$([CH2X4][cX3]1[cX3H][nX3H][cX3]2[cX3H][cX3H][cX3H][cX3H][cX3]12),
$([CH2X4][cX3]1[cX3H][cX3H][cX3]([OHX2,OH0X1-])[cX3H][cX3H]1),
$([CHX4]([CH3X4])[CH3X4])])[CX3](=[OX1])[OX2H,OX1-,N])]

Format is A.A.Template for 20 standard a.a.s. where * is replaced by the entire 18_standard_side_chains list (or'd together). A gen eric amino acid with any of the 18 side chains or, proline or glycine. Hits "standard" amino acids that have terminally appended groups (i.e . "standard" refers to the side chains). (Pro, Gly, or 18 normal a.a.s.) Hits single a.a.s and specific residues w/in polypeptides (intern al, or terminal).

Non-standard amino acid.

[$([NX3,NX4+][CX4H]([*])[CX3](=[OX1])[O,N]);!$([$([$([NX3H,NX4H2+]),
$([NX3](C)(C)(C))]1[CX4H]([CH2][CH2][CH2]1)[CX3](=[OX1])[OX2H,OX1-,N]),
$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H2][CX3](=[OX1])[OX2H,OX1-,N]),
$([$([NX3H2,NX4H3+]),$([NX3H](C)(C))][CX4H]([$([CH3X4]),$([CH2X4][CH2X4][CH2X4][NHX3][CH0X3]
(=[NH2X3+,NHX2+0])[NH2X3]),$([CH2X4][CX3](=[OX1])[NX3H2]),$([CH2X4][CX3](=[OX1])[OH0-,OH]),
$([CH2X4][SX2H,SX1H0-]),$([CH2X4][CH2X4][CX3](=[OX1])[OH0-,OH]),$([CH2X4][#6X3]1:
[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),$([#7X3H])]:
[#6X3H]:[$([#7X3H+,#7X2H0+0]:[#6X3H]:[#7X3H]),
$([#7X3H])]:[#6X3H]1),$([CHX4]([CH3X4])[CH2X4][CH3X4]),$([CH2X4][CHX4]([CH3X4])[CH3X4]),
$([CH2X4][CH2X4][CH2X4][CH2X4][NX4+,NX3+0]),$([CH2X4][CH2X4][SX2][CH3X4]),
$([CH2X4][cX3]1[cX3H][cX3H][cX3H][cX3H][cX3H]1),$([CH2X4][OX2H]),$([CHX4]([CH3X4])[OX2H]),
$([CH2X4][cX3]1[cX3H][nX3H][cX3]2[cX3H][cX3H][cX3H][cX3H][cX3]12),
$([CH2X4][cX3]1[cX3H][cX3H][cX3]([OHX2,OH0X1-])[cX3H][cX3H]1),
$([CHX4]([CH3X4])[CH3X4])])[CX3](=[OX1])[OX2H,OX1-,N])])]

Generic amino acid but not a "standard" amino acid ("standard" refers to the 20 normal side chains). Won't hit amino acids that are non-standard due solely to the fact that groups are terminally-appended to the polypeptide chain (N or C term). format is [$(generic a.a.); !$(not a standard one)] Hits single a.a.s and specific residues w/in polypeptides (internal, or terminal).

Recursive or Multiple

Recursive SMARTS: Atoms connected to particular SMARTS

Ortho

[SMARTS_expression]-!:aa-!:[SMARTS_expression]

Meta

[SMARTS_expression]-!:aaa-!:[SMARTS_expression]

Para

[SMARTS_expression]-!:aaaa-!:[SMARTS_expression]

Hydrogen

[$([#1][SMARTS_expression])]

Hydrogen must be explicit i.e. an isotope or charged

Nitrogen

[$([#7][SMARTS_expression])]

Oxygen

[$([#8][SMARTS_expression])]

Fluorine

[$([#9][SMARTS_expression])]

Recursive SMARTS: Multiple groups

Two possible groups

[$(SMARTS_expression_A),$(SMARTS_expression_B)]

Hits atoms in either environment or group of interest, A or B.
    Example usages:
    Azide group is : [$(*-[NX2-]-[NX2+]#[NX1]),$(*-[NX2]=[NX2+]=[NX1-])]
    Azide ion is: [$([NX1-]=[NX2+]=[NX1-]),$([NX1]#[NX2+]-[NX1-2])]
    Azide or azide ion is: [$([$(*-[NX2-]-[NX2+]#[NX1]),$(*-[NX2]=[NX2+]=[NX1-])]),$([$([NX1-]=[NX2+]=[NX1-]),$( [NX1]#[NX2+]-[NX1-2])])]

Recursive SMARTS

[$([atom_that_gets_hit][other_atom][other_atom])]

Hits first atom within parenthesis     Example usages:
    [$([CX3]=[OX1])] hits Carbonyl Carbon     [$([OX1]=[CX3])] hits Carbonyl Oxygen

Single only, Double only, Single or Double

Sulfide

[#16X2H0]

(-alkylthio) Won't hit thiols. Hits disulfides too.

Mono-sulfide

[#16X2H0][!#16]

(alkylthio- or alkoxy-) R-S-R Won't hit thiols. Won't hit disulfides.

Di-sulfide

[#16X2H0][#16X2H0]

Won't hit thiols. Won't hit mono-sulfides.

Two sulfides

[#16X2H0][!#16].[#16X2H0][!#16]

Won't hit thiols. Won't hit mono-sulfides. Won't hit disulfides.

Acid/conj-base

[OX2H,OX1H0-]

Hits acid and conjugate base. acid/base

Non-acid Oxygen

[OX2H0]

Acid/base

[H1,H0-]

Works for any atom if base form has no Hs & acid has only one.

Muntiple Disconnected Groups

Two disconnected SMARTS fragments

([Cl!$(Cl~c)].[c!$(c~Cl)])

A molecule that contains a chlorine and an aromatic carbon but which are not connected to each other. Uses component-level SMARTS. B oth SMARTS fragments must be in the same SMILES target fragment.

Two disconnected SMARTS fragments

([Cl]).([c])

Hits SMILES that contain a chlorine and an aromatic carbon but which are in different SMILES fragments.

Two not-necessarily connected SMARTS fragments

([Cl].[c])

Uses component-level SMARTS. Both SMARTS fragments must be in the same SMILES target fragment.

Two not-necessarily connected fragments

([SMARTS_expression]).([SMARTS_expression])

Uses component-level SMARTS. SMARTS fragments are each in different SMILES target fragments.

Two primary or secondary amines

[NX3;H2,H1;!$(NC=O)].[NX3;H2,H1;!$(NC=O)]

Here we use the "disconnection" symbol (".") to match two separate not-necessarily bonded identical patterns.

Tools &Tricks

Alternative/Equivalent Representations

Any carbon aromatic or non-aromatic

[#6] or [c,C]

SMILES wildcard

[#0]

This SMARTS hits the SMILES *

Factoring

[OX2,OX1-][OX2,OX1-] or [O;X2,X1-][O;X2,X1-]

Factor out common atomic expressions in the recursive SMARTS. May improve human readability.

High-precidence "and"

[N&X4&+,N&X3&+0] or [NX4+,NX3+0]

High-precidence "and" (&) is the default logical operator. "Or" (,) is higher precidence than & and low-precidence "and" (;) is lower precidence than &.

Hydrogens

Any atom w/ at-least 1 H

[*!H0,#1]

In SMILES and SMARTS, Hydrogen is not considered an atom (unless it is specified as an isotope). The hydrogen count is instead consi dered a property of an atom. This SMARTS provides a way to effectively hit Hs themselves.

Hs on Carbons

[#6!H0,#1]

Atoms w/ 1 H

[H,#1]

5. Electron & Proton Features

Acids & Bases

Acid

[!H0;F,Cl,Br,I,N+,$([OH]-*=[!#6]),+]

Proton donor

Carboxylic acid

[CX3](=O)[OX2H1]

(-oic acid, COOH)

Carboxylic acid or conjugate base.

[CX3](=O)[OX1H0-,OX2H1]

Hydroxyl_acidic

[$([OH]-*=[!#6])]

An acidic hydroxyl is a hydroxyl bonded to an atom which is multiply bonded to a hetero atom, this includes carboxylic, sulphur, pho sphorous, halogen and nitrogen oxyacids

Phosphoric_Acid

[$(P(=[OX1])([$([OX2H]),$([OX1-]),$([OX2]P)])([$([OX2H]),$([OX1-]),$([OX2]P)])[$([OX2H]),$([OX1-]),$([OX2]P)]),$([P+]([OX1-])([$([OX2H]),$([OX1-]),$([OX2]P)])([$([OX2H]),$([OX1-]),$([OX2]P)])[$([OX2H]),$([OX1-]),$([OX2]P)])]

Hits both forms. Hits orthophosphoric acid and polyphosphoric acid anhydrides. Doesn't hit monophosphoric acid anhydride esters (in cluding acidic mono- & di- esters) but will hit some polyphosphoric acid anhydride esters (mono- esters on pyrophosphoric acid and longe r, di- esters on linear triphosphoric acid and longer). Hits acid and conjugate base.

Sulfonic Acid. High specificity.

[$([#16X4](=[OX1])(=[OX1])([#6])[OX2H,OX1H0-]),$([#16X4+2]([OX1-])([OX1-])([#6])[OX2H,OX1H0-])]

Only hits carbo- sulfonic acids (Won't hit herteroatom-substituted molecules). Hits acid and conjugate base. Hits Both Depiction Fo rms. Hits Arene sulfonic acids.

Acyl Halide

[CX3](=[OX1])[F,Cl,Br,I]

(acid halide, -oyl halide)

Charge

Anionic divalent Nitrogen

[NX2-]

Oxenium Oxygen

[OX2H+]=*

Oxonium Oxygen

[OX3H2+]

Carbocation

[#6+]

sp2 cationic carbon.

[$([cX2+](:*):*)]

Aromatic cationic sp2 carbon with a free electron in a non-bonding sp2 hybrid orbital

Azide ion.

[$([NX1-]=[NX2+]=[NX1-]),$([NX1]#[NX2+]-[NX1-2])]

Hits N in azide ion

Zwitterion High Specificity

[+1]~*~*~[-1]

+1 charged atom separated by any 3 bonds from a -1 charged atom.

Zwitterion Low Specificity, Crude

[$([!-0!-1!-2!-3!-4]~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~*~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~*~*~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~*~*~*~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~*~*~*~*~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~*~*~*~*~*~*~[!+0!+1!+2!+3!+4]),$([!-0!-1!-2!-3!-4]~*~*~*~*~*~*~*~*~*~[!+0!+1!+2!+3!+4])]

Variously charged moieties separated by up to ten bonds.

Zwitterion Low Specificity

([!-0!-1!-2!-3!-4].[!+0!+1!+2!+3!+4])

Variously charged moieties that are within the same molecule but not-necessarily connected. Uses component-level grouping.

H-bond Donors & Acceptors

Hydrogen-bond acceptor

[#6,#7;R0]=[#8]

Only hits carbonyl and nitroso. Matches a 2-atom pattern consisting of a carbon or nitrogen not in a ring, double bonded to an oxyge n.

Hydrogen-bond acceptor

[!$([#6,F,Cl,Br,I,o,s,nX3,#7v5,#15v5,#16v4,#16v6,*+1,*+2,*+3])]

A H-bond acceptor is a heteroatom with no positive charge, note that negatively charged oxygen or sulphur are included. Excluded are halogens, including F, heteroaromatic oxygen, sulphur and pyrrole N. Higher oxidation levels of N,P,S are excluded. Note P(III) is currentl y included. Zeneca's work would imply that (O=S=O) shoud also be excluded.

Hydrogen-bond donor.

[!$([#6,H0,-,-2,-3])]

A H-bond donor is a non-negatively charged heteroatom with at least one H

Hydrogen-bond donor.

[!H0;#7,#8,#9]

Must have an N-H bond, an O-H bond, or a F-H bond

Possible intramolecular H-bond

[O,N;!H0]-*~*-*=[$([C,N;R0]=O)]

Note that the overall SMARTS consists of five atoms. The fifth atom is defined by a "recursive SMARTS", where "$()" encloses a valid nested SMARTS and acts syntactically like an atom-primitive in the overall SMARTS. Multiple nesting is allowed.

Radicals

Carbon Free-Radical

[#6;X3v3+0]

Hits a neutral carbon with three single bonds.

Nitrogen Free-Radical

[#7;X2v4+0]

Hits a neutral nitrogen with two single bonds or with a single and a triple bond.

6. Breakdown of Complex SMARTS