Hydroxylamine cleaving ester bonds

The hydroxyl version of the Rink amide linker, known as the Rink acid resin (25), was developed as a tool for the preparation of protected peptide fragments [13]. The peptide-linker ester bond is labile to extremely weak acids, such as HOBt or acetic acid, allowing peptides bearing t-butyl-based side-chain protection to be cleaved intact. Conversion of the hydroxyl group into chloride [66] or trifluoroacetyl [67] provides linkers that have been used for immobilization of various nucleophiles, including alcohols, N-protected hydroxylamines, phenols, purines, amines, anilines and thiols [66-68], The stability of the cation derived from this tinker is such that even thiols and amines can be cleaved from this tinker with TFA (Figure 14.12). 

Involvement of esters in the intermolecular cross-links accounts for the dissolution of mature collagen by hydroxylamine, hydrazine or alkali in the presence of hydrogen-bond breakers. Similarly, the participation of hexoses accounts for the dissolution of collagen by periodic acid and a hydrogen-bond breaker. Recently, it has been shown that collagen can be completely dissolved by some proteolytic enzymes (see Section II). These enzymes also cleave the intramolecular cross-links (Kiihn et al, 1963a Rubin et al., 1963). It appears therefore that either the crosslinks include a peptide chain or the chain close to the cross-links contains pepsin- and trypsin-sensitive bonds. 

This imine is stabilized by hydrogen bonding of the phenolic hydroxyl with the lone pair on the imine. This group is cleaved with strong acids such as HCl or with Me-ONH2/MeOH/CHCl3, which is preferred over the use of hydroxylamine because it is a poorer nucleophile and thus is compatible with esters. ... 

Numerous homobifunctional cross-linkers are available commercially (e.g. from Pierce), including disuccinimidyl derivatives (3, 4), water-soluble sulphodisuccinimidyl derivatives (5, 6), and diimido esters (7-9). Also available are cross-linkers containing bonds that can be cleaved by reduction (10, 11), hydroxylamine (12, 13), base (14), oxidation (15, 16), etc., which makes it possible to liberate the peptide from the conjugate for analytical purposes. 

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