Ester linker

Cleavage reagents Benzyl- type linkers Ketal/ acetal linkers Esters/ amide linkers Silyl linkers Triazene linkers Selenium/ sulfur/ stannane linkers... 

In the second route, a carboxylic acid at the para position of a benz-hydryl bromide is attached to the resin as an ester (Scheme 10). After constructing various molecules with different amines attached at the benzhydryl position, a facile aminolysis of the linker ester with A1C13 and diethylamine provided products with a para-diethylamide at the point of previous resin attachment. 

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). 

Poly(acrylic acid) and Poly(methacrylic acid). Poly(acryHc acid) (8) (PAA) may be prepared by polymerization of the monomer with conventional free-radical initiators using the monomer either undiluted (36) (with cross-linker for superadsorber appHcations) or in aqueous solution. Photochemical polymerization (sensitized by benzoin) of methyl acrylate in ethanol solution at —78° C provides a syndiotactic form (37) that can be hydrolyzed to syndiotactic PAA. From academic studies, alkaline hydrolysis of the methyl ester requires a lower time than acid hydrolysis of the polymeric ester, and can lead to oxidative degradation of the polymer (38). Po1y(meth acrylic acid) (PMAA) (9) is prepared only by the direct polymerization of the acid monomer it is not readily obtained by the hydrolysis of methyl methacrylate. 

Formulations for acryHc copolymers involve monomers such as acryHc acid [79-10-7], methacrylic acid [79-14 ], or esters of these acids. Formation of a copolymer from a methylmethacrylate ester (3), where DVB serves as the cross-linker, gives the stmctures ... 

As of this writing (1997), researchers are exploring combinations of acids, additives, and catalysts to achieve a suitable economic finish. However, commercial appHcation of these finishes would require costs akin to that of DMDHEU as well as compliance with formaldehyde release levels by consumers, regulators, and the textile industry. Another possible impetus could be marketing considerations. Nevertheless, this work has sparked intense effort in the use of cross-linkers containing ester cross-links and has broadened the scope of cross-linker research. 

Polymerization screening mns using porphyrin catalysts with different linker groups between the 700 Da polyethylene tail and the porphyrin core showed little variability. The catalytic activity for the 4 x 700 PE porphyrin catalysts with ether (5), ester (7) or polyether (8) linkers was nearly identical, with only small differences in the resin colors being noted (Figures 36.3 and 36.4). These results are consistent with literature findings that porphyrin CCT catalysts are relatively insensitive to functional groups on the equatorial plane. ... 

Silyl-derived linker 36 was prepared in three steps from a silyl ether of serine and incorporated for Fmoc/tBu-based assembly of protected gly-copeptide blocks (Scheme 11) [42]. The a-carboxylic acid function of serine was protected as an allyl ester. Deprotection by a Pd(0) catalyst in the presence of dimedone liberated the carboxylic acid in order for subsequent... 

Aryl hydrazide linker 38 stable to both acid and base was utilized in SPPS [46], Treatment of the resin with a copper(II) catalyst in the presence of a base and nucleophile gave the corresponding acid, amide, or ester (Scheme 13). 

Staros, J.V. (1982) N-hydroxysulfosuccinimide active esters Bw(N-hydroxysulfosuccinimide) esters of two dicarboxylic acids are hydrophilic, membrane impermeant, protein cross-linkers. Biochemistry 21, 3950-3955. 

Condensation of aromatic or aliphatic esters with resin-supported acetyl carboxylic acids 28 followed by cyclisation with hydroxylamine, activation of the linker, and cleavage using amines, provided highly substituted isoxazoles 30 and 31. This general method gave products in excellent yields and purities in which the regioisomers ratio can be easily controlled . 

---