Solid-phase procedure

Elongation of the peptide chain in the direction of the N-terminal by a solid-phase procedure was introduced by Lavielle and coworkers,132 who prepared the glycopeptide [3-0-(2-acetamido-2-deoxy-/ -D-gluco-pyranosyl)-L-serine]-L-glycyl-L-alanine (189) by first coupling 168, de-protected by hydrogenolysis, to an L-alanyl resin (188), and, after re-... 

For the development of an appropriate strategy for cleavage from the novel syringaldehyde resin, the authors adapted a previously elaborated solution-phase model study on intramolecular Diels-Alder reactions for the solid-phase procedure (Scheme 7.60). The resulting pyridines could be easily separated from the polymer-bound by-products by employing a simple filtration step and subsequent evaporation of the solvent. The remaining resins were each washed and dried. After drying,... 

PE Thompson, HH Keah, PT Gomme, PG Stanton, MTW Hearn. Synthesis of peptide amides using Fmoc-based solid-phase procedures on 4-methylbenzhydrylamine resins. Int J Pept Prot Res 46, 174, 1995. 

The polymer-bound p-nitrobenzophenone oxime (71d) has been found to be a suitable support for stepwise peptide synthesis. Protected peptides can be assembled on 70d by coupling and deprotection steps similar to those employed in the usual Merrifield solid-phase procedures (Scheme 39). Cleavage of peptides from 71d can be accomplished with hydrazine and amino acid esters under mild conditions, which do not affect benzyl ester side-chain protecting groups. 

Methyluracils 947 are readily prepared by reaction of ureas with diketene 945 in acetic acid, and although mixtures of products are obtained with substituted ureas, this procedure has been used synthetically to prepare a variety of 1-substituted and 1,3-disubstituted 6-methyluracils, using both solution- and solid-phase procedures <2000TL1487, 2003CPB1025, 2004JME1259>. 

In a parallel study, Wipf and Fritch11041 have shown that also urethane-protected (Boc), and even amino acid segments, are tolerated as acyl compounds on the aziridine nitrogen. The best results were obtained with alkylcopper reagents derived from CuCN and an alkyl-lithium in the presence of boron trifluoride-diethyl ether complex. Some 6-alkylated compounds (11-15%) were isolated as well. This work was extended to a solid-phase procedure that resulted in resin-bound alkene isosteres that could immediately be used in further peptide synthesis.11051 For this purpose, the 2-nitrophenylsulfonyl (oNbs) group was used for nitrogen protection and aziridine activation. It could be readily cleaved with benzenethio-late, which was compatible with the acid-sensitive Wang linker used. 

The sequence of solid-phase assembly and cyclization reactions used to prepare the bis(Ampa)-bridged peptide 31 is summarized in Scheme 19. All solid-phase procedures were performed in a standard, custom-built, 200-mL capacity, manual peptide synthesis reaction vessel. 165 ... 

The synthetic strategies used for the preparation of pyrans on insoluble supports have mainly been hetero-Diels-Alder reactions of enones with enol ethers and ringclosing olefin metathesis (Table 15.33). Benzopyrans have been prepared by hetero-Diels-Alder reactions of polystyrene-bound o-quinodimethanes with aldehydes. The required quinodimethanes were generated by thermolysis of benzocyclobutanes, which were prepared in solution [308]. Other solid-phase procedures for the preparation of benzopyrans are the palladium-mediated reaction of support-bound 2-iodo-phenols with 1,4-dienes (Entry 5, Table 15.33) and the intramolecular Knoevenagel... 

Experiments directed at a solution-phase synthesis were carried out as early as 1967,1[1,2 and a solid-phase/solution-phase synthesis of the inactive, nephrotoxic bacitracin F was also carried out.13 The first total synthesis of bacitracin A (3), a solid-phase procedure, was reported in 1996.[41... 

The first expeditious solid-phase procedure for the preparation of optically active quaternary r/.v- 3-lactams with an innovative substitution pattern is reported by Gonzalez-Muniz et al. [214]. They describe an operationally simple four-step procedure for the solid-phase synthesis of chiral (3S,4S)-l,3,4,4-tetrasubstituted p-lactams. Taking into account the recurrence of 1,3,4-trisubstituted pattern in bioactive monocyclic (3-lactams, the development of an environment friendly method for the synthesis of this 1,3,4,4-analogues may be of major interest. The key step to the four-member ring formation is the enantioselective phosphazene base-assisted cyclization of the resin-bound /V-(alky 1)-W- [(5)-2-ch Ioropropiony 1 ]... 

Synthesis of octreotide and derivative thereof can be carried out by two methods. The first method is synthesized initially by fragment condensation solution phase procedures. The synthetic process of octreotide has been described by Bauer et al. (1). The second method is the synthese by solid-phase procedures. Edward et al. (2) isolated side chain protected octreotide with a total yield of 14% by cleaving the protected peptide from the resin with threoninol. Arano et al. (3) carried out another solid phase method for octreotide, and produced it in overall 31.8% yield based on the starting Fmoc-Thr(tBu)-ol-resin. The basic difference from the other procedures already described is that the introduction of the threoninol is carried out upon the protected peptidic structure (resin-free), which, when appropriately activated, leads quantitatively and without needing to make temporary protections upon the threoninol, to the protected precursor of octreotide, which in turn, with a simple acid treatment leads to octreotide with very high yields. 

The split-mix method was developed for preparing peptide libraries. The method is based on Merrifield s solid phase procedure, published in 1963 [8], Each coupling cycle of the solid phase synthesis is replaced by the following simple operations ... 

In the split-mix synthesis, like in other solid phase procedures, the beads behave very much like tiny reaction vessels, which do not interchange their contents with the other ones. Each of the millions of these reaction vessels preserves its content until the end of the synthesis, when they become containers of a single substance. If peptides are produced, their identity can be determined by automatic sequencing [9], It is sufficient to sacrifice a fraction of the total quantity for this purpose. All this means that the split-mix synthesis is, in fact, a parallel procedure, with unprecedented efficiency, however, leading to individual compounds. This feature of the split and mix synthesis allows screening the products in three different ways ... 

Endorphins from a variety of species (even ostrich)018 have now been isolated/50 200 Human /3-endorphin (/3H), which diflers from most animal untriakontapeptide in having Tyr at position 87 instead of His, and Glu at 91 in place of Gin, has been synthesized by the solid-phase procedure/119 When applied centrally, /3H-endorphin was 17-48 times more potent than morphine in mice and 3.4 times more potent after the iv route by MTF, MHP, and WR tests naloxone blocked the analgesic responses. 

The A chain was synthesized by the automated solid-phase procedure (94). Three grams of A -Boc-Asn resin was carried through 20 reaction cycles as described for the B chain except that the reagents used for all deprotection and neutralization steps were 4M HCl in dry dioxane and triethylamine in CHCI3, respectively (95). The peptide was cleaved from the resin as described above (yield, 69%). The total time required was 8 days. The S-benzyl protecting groups were removed by treatment with sodium in liquid ammonia (96), and the four cysteine residues were converted to the S-sulfonates (ASSOB) (over all yield, 37%). 

The first synthesis reported by Merrifield produced the desired tetrapeptide (Leu-Ala-Gly-Val).f l Amino acids, dipeptides, and tripeptides were all detected in the crude product released from the resin. Through continued improvements of the method, the high speed of the amino acid incorporation and automation, the solid-phase peptide synthetic methodology has become the method of choice for most laboratories synthesizing peptides. Shortly after the introduction of the solid-phase procedure it was used to synthesize insulin. This impressive achievement awakened the biochemical community to the promise of synthetic chemistry and initiated a period in which large numbers of peptide analogues were prepared and analyzed. 

The Fmoc group lends itself particularly to the solid-phase procedure and is used almost exclusively in this mode. This is because in the deprotection reaction the initially formed dibenzofulvene moiety is efficiently scavenged by the secondary amine, usually piperidine, used for cleavage and is then washed away effectively from the solid support, whereas in solution phase the resulting moieties are not readily removed. However, the group still finds occasional utility in solution phase.t ... 

Most of the commonly applicable methods for activating the carboxy group of Fmoc amino acids to form amide bonds in solid-phase synthesis have been explored. Generally speaking, most methods are suitable but, in practice, relatively few methods are routinely used especially when scale-up of Fmoc/tBu solid-phase procedures are of prime consideration. Methods employed can be grouped into four classes ... 

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