Solid-phase polyamide synthesis

E Atherton, V Wooley, RC Sheppard. Internal association in solid phase peptide synthesis. Synthesis of cytochrome C residues 66-104 on polyamide supports, (trif-luoroacetyl) J Chem Soc Chem Commun 970, 1980. 

PolyHIPE has found a successful application in the field of solid phase peptide synthesis (SPPS), where the highly porous microstructure acts as a support material for a polyamide gel [134]. The polystyrene matrix is functionalised to give vinyl groups on its internal surfaces, and is then impregnated with a DMF solution of N, JV -dimethylacrylamide, acryloylsarcosine methyl ester, crosslinker and initiator. Polymerisation grafts the soft gel onto the rigid support, giving a novel composite material (Fig. 16). 

In 1971, Sheppard proposed that peptide synthesis would proceed more efficiently if the polymeric support was designed to have solvation properties similar to those of the peptide product.This line of reasoning led to the development of polyamide resins.The most successful of this type of support is based on cross-linked poly(dimethylacrylamide) (Pep-syn). Polyamide resins swell up to 10 times their dry volume in dimethylformamide and even more in water. On the other hand, they swell much less in dichloromethane. The few comparative studies that have been carried out between polystyrene and polyamide resins indicate that both give very similar results in routine solid-phase peptide synthesis. 

The behavior and properties of PNA oligomers should be considered prior to a discussion of the oligomer synthesis. PNA is constructed with a polyamide backbone and oligomers are prepared by traditional solid-phase peptide synthesis (SPPS) techniques. The terminal amino group of the PNA... 

The choice of polymer support is the most crucial factor in solid-phase oligonucleotide synthesis. Various types of supports used by different workers are summarized in Tables 5-1 and 5-2. Although most reported uses of polymers in nucleotide syntheses are styrene-based supports (both insoluble and soluble), other polymers such as polyamides, poly(ethyIene glycol), vinylacetate-V-vinylpyrrolidone copolymer, poly(vinyl alcohol), Sephadex LH20, and silica gel have also been used. 

Solid Phase Peptide Synthesis (SPPS). Pentafluorophenyl esters have been used in both solution and solid phase peptide synthesis. So far, only solution methods have been considered. The principal of SPPS is incorporation of single amino acid residues into peptide chains built on insoluble polymeric supports. The famous Merrifield paper started the tradition of SPPS using f-butoxycarbonyl (Boc) amino acids activated with 1,3-Dicyclohexylcarbodiimide, although this has now been superseded with the introduction of the Fmoc group in polystyrene-and polyamide-based SPPS. The theory of SPPS will not be discussed here. Needless to say, the use of pentafluorophenyl esters in SPPS was inevitable and was first reported by Atherton in 1985. Fmoc-amino acid pentafluorophenyl active esters were used in the polyamide solid phase series in polar DMF solutions in the presence of 1-Hydroxybenzotriazole as a catalyst. 

The amino acid 58 was used in the solid-phase synthesis of sequence-specific DNA binding polyamides containing N-methylimidazole and N-methylpyrrole amino acids <96JACS6141> and it was also reported that the imidazole-acridine conjugate 59 could effectively catalyze the cleavage of t-RNA <96TL4417>. 

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...

Baird, E.E. and P.B. Dervan. Solid phase synthesis of polyamides containing imidazole and pyrrole amino acids./. 

WvRTZ, N.R., J.M. Turner, E.E. Baird, and P. B. Dervan. Fmoc solid phase synthesis of polyamides containing pyrrole and imidazole amino acids. Org. Lett. 2001, 3, 1201-1203. 

Belitsky, J.M., D. H. Nguyen, N. R. WuRTZ, and P. B. Dervan. Solid-phase synthesis of DNA binding polyamides on oxime resin. Bioorg. Med. Chem. 2002,... 

Atherton E, Logan CJ, Sheppard RC, Peptide synthesis, part 2 Procedures for solid phase synthesis using W-lluorcnylmcthoxycarbon-ylamino acids on polyamide supports Synthesis of substance P and of acyl carrier protein 64—74 decapeptide. J Chem Soc Perkin Trans 1 1981 ... 

E Atherton, M Caviezel, H Fox, D Harkiss, H Over, RC Sheppard. Peptide synthesis. Part 3. Comparative solid-phase synthesis of human P-endorphin on polyamide supports using t-butoxycarbonyl and fluorenylmethoxycarbonyl. 

E Atherton, MJ Gait, RC Sheppard, BJ Williams. The polyamide method of solid phase peptide and oligonucleotide synthesis. Bioorg Chem 8, 351-370, 1979. 

The solid-phase synthesis of dendritic polyamides was explored by Frechet et al. [49]. Inspired by the technique used by Merrifield for peptide synthesis, the same strategy was used to build hyperbranched polyamides onto a polymeric support. The idea was to ensure the preservation of the focal point and to ease the purification between successive steps. The resulting polymers were cleaved from the solid support, allowing ordinary polymer characterization. The reaction was found to be extremely sluggish beyond the fourth generation. 

Frechet et al. reported on the solid-phase synthesis of dendritic polyamides in 1991 [49]. The intention was to grow dendritic segments from a sohd support and thereby enhance the ease of purification between successive steps (Sect. 2.2). 

The synthesis of a pyrrole segment common to netropsin and distamycin is shown in Scheme 2ji°l Friedel-Crafts acylation of 1-methylpyrrole (1) followed by nitration at C4 provides 3 in 54% yield. After a haloform reaction, hydrogenolysis, N-protection with B0C2O, and saponification, the pyrrolecarboxylic derivative acid 7 was obtained in 30% overall yield from 3. This monomer is readily chain-extended to the pyrrole-imidazole derivative 9 (Scheme 3)J10 Furthermore, solid-phase synthesis with this and related pyrrole-containing building blocks leads to polyamides that have recently been used in the recognition of a 16 base-pair sequence in the minor groove of DNA.1" ... 

In the present context, solid-phase synthesis has been used primarily for the preparation of peptide and glycopeptide dendrimers [23]. For example, a second-generation dendrimer could be prepared by successive addition of branched polyproline building blocks to a solid phase [24]. The divergent synthesis of polyamide dendrimers on polystyrenes was accomplished [25] by Frechet el al. 1991 (cf. Fig. 2.8) [26]. PAMAM dendrons could be grown up to the fourth-... 

Kitas, E.A., Perich, J.W., Wade, J.D., Johns, R.B., and Treagear, G.W. (1989) Fmoc-polyamide solid phase synthesis of an O-phosphotyrosine-containing tride-capeptide. Tetrahedron Lett. 30, 45, 6229-6232. 

Detailed investigations of different polyacrylamides as supports for the synthesis of peptides and oligonucleotides helped Atherton et al. to define the following requirements for polyamide supports to be suitable for the solid phase peptide synthesis53). 

The advantage of these reagents relies on their simplicity of use. An equivalent of the reagent is added to a 1 1 mixture of the carboxylic component and tertiary base in an inert solvent at room temperature. The mixing can be carried out in the presence of the amino component. These coupling reagents are compatible with Z, Boc, and Fmoc chemistry, solution and solid-phase synthesis, polystyrene, polyamide, and continuous flow resins. 

The rapid solid-phase synthesis of pyrrole-imidazole polyamides with a wide variety of sequences and the generation of combinatorial libraries should increase the possibilities for the recognition of any desired DNA double strand. 

A related cyclization was recently reported by Jia et al. [14] with allylamine 20 immobilized on poly styrene-Wang resin. The reaction was monitored by acetylation and cleavage to yield 21, as a mixture of free and Boc-protected amines. This solid-phase synthesis of. seco-CBI (21, R = H), related to the pharmacophore of the CC-1065 and duocarmycin class of cyclopropylindole antitumor antibiotics, has potential for the preparation of analogue libraries, and an example of further transformation of resin-bound 21 to a polyamide was presented. 

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