Wang-resin

The details of the solid-phase technique have been improved substantially over the years, but the fundamental idea remains the same. The most commonly used resins at present are either the Wang resin or the PAM (phenyl-acetamidomethyl) resin, and the most commonly used N-protecting group is the fluorenylmethyloxycarbonyl, or Fmoc group, rather than Boc. 

Solid-phase peptide synthesis. 1036-1038 PAM resin in. 1037 Wang resin in, 1037 Solvation, 370... 

Walden, Paul, 360 Walden inversion. 359-360 Wang resin, solid-phase peptide synthesis and. 1037 Water, acid-base behavior of, 50 dipole moment of, 39 electrostatic potential map of. 53 nucleophilic addition reactions of, 705-706 pKaof, 51-52... 

To generate molecular libraries, a series of 5-oxo-2-azabicyclo[2.2.2]octane and triaza analogs were prepared via a stereospecific Diels-Alder reaction by reacting Wang-resin-bound diene 35 with a variety of dienophiles [28]. After removing the solid support with a strong acid, adducts 36 were isolated examples of reactions that have furnished the best yields are reported in Scheme 4.6. 

Microwave irradiation has been used to accelerate the Gewald reaction for the one-pot synthesis of N-acyl aminothiophenes on solid support [67]. A suspension of cyanoacetic acid Wang resin 35, elemental sulfur, DBU and an aldehyde or ketone 36 in toluene was irradiated for 20 min at 120 °C in a single-mode microwave synthesizer (Scheme 13). Acyl chloride 37 was added, followed by DIPEA, and the mixture was irradiated for 10 min at 100 °C. After cooling to room temperature, the washed resin was treated with a TEA solution to give M-acylated thiophenes 38 in 81-99% yield and purities ranging from 46-99%. 

Rapid loading of cross-linked PS Wang resin (4-(benzyloxy)benzyl alcohol PS) with a selection of /3-ketoesters was shown to reach completion within 1-10 min if microwave irradiation at 170 °C was employed. The conventional thermal method for acetoacetylation of hydroxymethyl-functionalized polystyrene resins takes several hours therefore, microwave heating allowed for... 

Fig. 5 Microwave-assisted loading protocol of carboxylic acids to chlorinated polystyrene Wang resin...

The imidazole ring is a privileged structure in medicinal chemistry since it is found in the core structure of a wide range of pharmaceutically active compounds efficient methods for the preparation of substituted imidazole libraries are therefore of great interest. Recently, a rapid synthetic route to imidazole-4-carboxylic acids using Wang resin was reported by Henkel (Fig. 17) [64]. An excess aliphatic or aromatic amine was added to the commercially available Wang-resin-bound 3-Ar,M-(dimethylamino)isocyano-acrylate, and the mixture was heated in a sealed vial with microwave irradi-... 

Wang linker, mimic 297 Wang resin, phthalimide library synthesis 103... 

It was also shown that the commercially available Wang resin is well suited for the reaction, but a tailor-made resin (based on syringealdehyde and Mer-rifield resin) offers milder cleavage conditions. By comparing conventional heating versus MAOS it was found that similar yields for the cycloaddition step were obtained, but the cleavage from the resin can be performed under much milder conditions when microwave irradiation is used, and in some cases the procedure only works using the microwave technique (Table 1). 

The investigation of minor groove-binding polyamides was greatly accelerated by the implementation of solid-phase synthesis [48]. Originally demonstrated on Boc-y9-Ala-PAM resin with Boc-protected monomers, it was also shown that Fmoc chemistry could be employed with suitably protected monomers and Fmoc-y9-Ala-Wang resin (Fig. 3.8) [49]. Recently, Pessi and coworkers used a sulfonamide-based safety-catch resin to prepare derivatives of hairpin polyamides [50]. Upon activation of the linker, resin-bound polyamides were readily cleaved with stoichiometric quantities of nucleophile to provide thioesters or peptide conjugates. 

Fig. 3.8 Variations to solid phase synthesis of polyamides. Use of Fmoc monomers on jS-Ala-Wang resin (left) provides polyamides containing a jS-alanine residue near the C-ter-mini. Polyamides synthesized on the Kaiser...

Aminosulfonyl ureas were constructed from a sulfonylcarbamate linkage (Scheme 31) [72], Reaction of chlorosulfonyl isocyanate (CSI) with Wang resin provided a chlorosulfonylcarbamate 63 which was then converted to substituted amino sulfonylcarbamate compounds by reaction with excess amines. The final aminosulfonyl urea products were cleaved from the resin by treatment with amines in HF at reflux temperature for overnight. 

Domino radical transformations on solid support can also be used, as shown by Naito and coworkers [18]. Thus, immobilized oxime ether 10-55 (Wang resin) afforded the tetrahydrofuranones 10-57 after removal of the resin, when it was exposed to BEt3 in the presence of different alkyl iodides 10-56 (Scheme 10.14). 

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