Reactive groups

NHS esters

N-Hydroxysuccinimide (NHS) esters are reactive species which couple with amines efficiently. This type of activated esters is particularly suitable for the labeling of biomolecules in aqueous environments.

STP esters

Sulfotetrafluorophenyl ethers (STP ethers) are reactive derivatives that react efficiently with primary amines to form the same acylation products as NHS esters. They are dramatically more water-soluble than the corresponding N-hydroxysuccinimidyl (NHS) esters, making them ideal for labeling biomolecules in an aqueous environment.

TFP esters

Tetrafluorophenyl ethers (TFP ethers) are reactive derivatives that react efficiently with primary amines to form the same acylation products as NHS esters. They are more stable at the basic pH values typically associated with reactions with amines and are also less susceptible to spontaneous hydrolysis.

Azides

Azides are used for the conjugation with alkynes in copper-catalyzed (CuAAC) reactions with terminal alkynes and in copper-free (strain promoted, SPAAC) click reactions with strained cycloalkynes.

Alkynes

Terminal alkynes for the copper-catalyzed click chemistry reaction with azides (Cu-catalyzed alkyne-azide cycloaddition, CuAAC). The reaction is highly efficient and specific. Terminal alkynes and azides are very rarely encountered in natural molecules and need to be introduced specially for the labeling reaction to take place.

Cycloalkynes

Cycloalkynes are reactive derivatives for SPAAC conjugation reaction, strain-promoted alkyne–azide cycloaddition.

Tetrazines

Tetrazine (1,2,4,5-tetrazine) is a six-membered cyclic system with four nitrogen atoms. Tetrazines react extremely fast with terminal alkenes and trans-cyclooctenes in tetrazine-alkene and tetrazine-TCO ligations, so-called Inverse electron demand Diels-Alder ligation (IEDDA). Tetrazines also react with some strained cycloalkynes.

Cycloalkenes

Cycloalkenes are strained alkenes, tetrazine-reactive derivatives for inverse electron-demand Diels-Alder cycloaddition reaction (IEDDA).

Hydrazides

Hydrazides react with aldehyde and ketone groups. Many natural carbohydrates possess open forms containing carbonyl groups. Carbonyl groups can also be generated from 1,2-diols (such as most carbohydrates) by periodate oxidation. Aldehydes formed this way can be labeled with hydrazides - this is an especially useful method to label glycoproteins.

Thiols

Thiol (SH, sulfhydryl) group, also known as the mercapto group, is a very reactive nucleophilic group useful for bioconjugation.

Amines

Amino groups react with various electrophilic reagents ranging from NHS esters to epoxides. Amines participate in reductive amination and enzymatic transamination reactions which can be sometimes useful for the biolabeling.

Maleimides

Maleimides react with thiols (sulfhydryl groups) encountered in biomolecules such as proteins and peptides as cysteine residues. Maleimide labeling is efficient and site-specific. Natural cystines containing disulfide bonds need to be reduced in order to be labeled with maleimides.

Carboxylic acids

A free carboxylic acid group can be considered inert in most conditions. Therefore, carboxy dyes are useful for calibration and control experiments. However, carboxy groups can be specially activated for labeling reactions – for example with carbodiimide and DMAP in a Steglich esterification.

Halides

Products containing halide functional groups for bioconjugation tasks. The halide group participates in nucleophile substitution reactions and can readily and efficiently interact with various C-, O-, N-, S-centered, and other nucleophiles.

Phosphoramidites

Phosphoramidites are reagents for the automated oligonucleotide synthesis. A variety of modifying amidite building blocks are available for the preparation of highly complicated oligonucleotides, enabling subsequent advanced bioanalytical and bioengineering applications.