McTONY Bio&Chem Inc.

Wang Resins

Wang support is the most widely used resin in SPOC. Attachment of carboxlic acid can be achieved with DCC/DMAP or 2,6-dichlrobenzoyl chloride/pyridine. Cleavage of esters involves concentrated TFA or TFA-DCM to provide the corresponding carboxylic acids. A general method of coupling and cleaving primary, secondary and tertiary alcohols was reported. In this method, the polymeric benzylic alcohol is converted into the reactive Wang trichloroacetimidate, which couples with the chosen alcohol in the presence of catalytic amounts of mild Lewis acid. Alcohol is cleaved from the Wang resin by treatment with 10% TFA-DCM for 30 min at ambient temperature. Conditions under which such Wang ethers are stable include Grignard reactions, ester sponification with lithium hydroxide, Weinreb amide formation, Mitsunobu reactions and enolate alkylations, as well as Heck reactions.

Merrifield Resins

The poly Merrifield resin was the standard support for the synthesis of peptide acids by Boc SPPS. In peptide chemistry, it is now really only used in the synthesis of small to medium sized peptides, as the benzylic ester resin linkage is not completely stable towards repetitive treatment with TFA.
Attachment of the C-terminal residue is generally achieved by heating the resin in DMF with the appropriate amino acid cesium salt in the presence of KI; although, Me₄N salts, sodium salts in THF with Bu₄NF catalysis and, more recently, zinc salts in EtOH have also been used.
Cleavage is normally effected by treatment of resin with HF or TFMSA, or by hydrogenolysis. Alcohols can be released using reducing agents such as DIBAL or LiBH₄. Methyl esters can be produced by transesterification with methoxide.

Resins with Functional Groups as Scavengers

Resins with functional groups can be used as scavengers for the removal of residues of crude reaction products by solution-phase syntheses. The use of scavenger resins makes it possible to remove the impurities by a single filtration.