CAS 56909-02-5

According to Sharpless (2001), click reactions must be modular, wide in scope, high-yielding, generate only inoffensive byproducts, be stereospecific, and use readily available starting materials. They should proceed under simple conditions (ideally insensitive to oxygen and water), use benign solvents, and products should be easy to isolate without chromatography.

For in vitro bioconjugation: CuAAC is the gold standard. For live-cell work: use SPAAC or IEDDA (copper-free). For protein labeling: SuFEx or Staudinger ligation. For polymer chemistry: thiol-ene or thiol-Michael. For prodrug activation: click-to-release (IEDDA-based elimination). Consider reaction speed, biocompatibility, and orthogonality requirements.

Most click reactions are compatible with aqueous conditions. CuAAC works in water/t-BuOH mixtures. SPAAC and IEDDA proceed rapidly in pure aqueous buffer. Thiol-ene reactions can be performed in water with water-soluble photoinitiators. SuFEx reactions work in organic/aqueous biphasic systems. This aqueous compatibility is one of the key advantages of click chemistry for biological applications.

For CuAAC/SPAAC: disappearance of the azide stretch at ~2100 cm⁻¹ in IR spectroscopy. For IEDDA: loss of the tetrazine UV-Vis absorption (pink color fades). General methods: TLC, HPLC, ¹H NMR (triazole peak), and mass spectrometry. For bioconjugation: SDS-PAGE with fluorescent readout or western blot.

Azides: 6–12 months at −20 °C (avoid light). Terminal alkynes: 12+ months at −20 °C. Cyclooctynes (DIBO, DBCO, BCN): 6–12 months at −20 °C (light-sensitive). Tetrazines: 6–12 months at −20 °C (light and moisture sensitive). TCO derivatives: 3–6 months at −20 °C (isomerization-prone). Sulfonyl fluorides: 12+ months at room temperature.