Solid phase synthesis of C-terminal peptide amides: development of a new aminoethyl-polystyrene linker on the Multipin solid support.

A new aminoethyl-polystyrene linker, stable at low concentrations of TFA, has been developed for the solid phase synthesis of peptide amides. The described linker is stable under conditions which remove Bu(t) protecting groups (30-50% TFA in DCM) and the desired product can be finally cleaved off the solid support in 95% TFA (5% H2O). Model peptide amides and other N-alkylated peptide amides have been successfully synthesized in good yield and purity.

Acetophenone-based linker for solid-phase peptide synthesis.

A new and cost-effective linker for the generation of carboxylic acid end groups on Multipin supports (SynPhase crowns) has been developed. Synthesis of the linker was based on modification of grafted polystyrene (PS) crowns to generate a hydroxyethyl moiety which is acid labile in 10-20% trifluoroacetic acid (TFA) in dichloromethane (DCM). Solid-phase syntheses of model decapeptides using this linker are described.

Solid phase synthesis of peptide aldehyde protease inhibitors. Probing the proteolytic sites of hepatitis C virus polyprotein.

The solid phase synthesis of a set of peptide aldehydes derived from the NS5A/NS5B junction of hepatitis C virus (HCV) viral polyprotein is demonstrated using an oxazolidine linker and the Multipin method. Deletion of the P6 and P5 residues results in a dramatic loss of inhibitory activity.

Novel alpha-hydroxyethyl-polystyrene, alpha-chloroethyl-polystyrene and alpha-amino-oxyethyl-polystyrene linkers on the Multipin solid support for solid-phase organic synthesis.

A simple method for the generation of three novel linkers, alpha-hydroxyethyl-polystyrene, alpha-chloroethyl-polystyrene and alpha-amino-oxyethyl-polystyrene on Multipin supports (SynPhase Crowns) has been developed. Applications of these linkers have been successfully demonstrated for solid-phase synthesis of dipeptide, oxime, and hydroxamic acid compounds in good yields and purities.

Comparative study of reductive amination reaction on 5-(4-formyl-3,5-dimethoxyphenoxy)valeric acid and its monomethoxy analog using the Multipin approach.

The 5-(4-formyl-3,5-dimethoxyphenoxy)valeric acid (Barany) linker and its monomethoxy analog were applied to the Multipin method of solid phase synthesis. A comparative assessment of reductive amination and cleavage of these linkers under conditions of multiple synthesis indicated that both were applicable to a broad range of primary amines including aniline and 4-nitroaniline. Apart from the greater lability of the dimethoxy version under TFA cleavage, there was no observable advantage of one linker over the other within the described experiment.

Multipin solid-phase synthesis of acyl 2, 3-diaminopropionic acid oligomers.

A modular approach for the synthesis of sets of diverse organic molecules is described. N-alpha-Fmoc-N-beta-Alloc-D-2,3-diaminopropionic acid (Fmoc-D-Dpr(Alloc)-OH) was prepared in four steps from Boc-D-asparagine and used as a scaffold for attachment of sidechains. Using the Multipin approach, a number of model acyl trimers were rapidly prepared by sequential coupling of Fmoc-D-Dpr(Alloc)-OH and acylation of the beta-amino group with a range of activated carboxylic acids.

Larger scale multipin peptide synthesis.

The multipin peptide synthesis approach originated as an immunological tool for epitope mapping. However, continuing evolution of the basic technology has allowed synthesis at scales up to 10 mumol per pin. At this loading, the methodology can no longer be considered just a screening tool. The overall synthesis efficiency of this approach was assessed by the synthesis of 2913 different peptides having little or no sequence homology and ranging up to a 46-mer in length. High performance liquid chromatography analysis of the crude peptides indicates overall quality of synthesis was high. The method is suitable for multi-milligram synthesis of peptides without sacrificing any of the inherent advantages of the 96-well format.

Multiple synthesis by the multipin method as a methodological tool.

The multipin method of peptide synthesis is demonstrated as a potent methodological tool, where large numbers of comparative studies can be performed concurrently. Two studies are presented. In each study, the test peptides were simultaneously synthesized, and the products examined by high throughput ion spray mass spectrometry and reverse-phase HPLC. In the first study, comprising 24 experiments, peptides 1 (AELFSTHYLAFKEDYSQ-NH2) and 2 (LKDFRVYFREGRDQLWKGPG-NH2) were prepared using Fmoc-Axx/BOP/HOBt/NMM [100 : 100 : 100 : 150 mM) and Fmoc-AXX/HATU/HOAt/NMM (100 : 100 : 100 : 150 nM) with 60, 90 and 120 min coupling times. The two reagent combinations were found to give comparable results. The second study compared the N-terminal coupling of Fmoc-Asn-OH, Fmoc-Asn(Mbh)-OH, Fmoc-Asn(Mtt)-OH, Fmoc-Asn(Tmob)-OH and Fmoc-Asn(Trt)-OH in the synthesis of seven test peptides: 3, NVQAAIDYIG-cyclo(KP): 4. NTVQAAIDYIG-cyclo(KP): 5. NRVYVHPFNL: 6. NRVYVHPFHL: 7. NEAYVHDAPVRSLN: 8. NQLVVPSEGLYLIYSQVLFK; 9, NPNANPNANPNA. A total of 33 experiments were performed. Peptides 3 and 4 were selected to highlight the effect of steric bulk of each Asn derivative on coupling efficiency. Reagent efficiency, as measured by target peptide purity, was as follows: Fmoc-Asn(Tmob)-OH > Fmoc-Asn-OH > Fmoc-Asn(Mtt)-OH = Fmoc-Asn(Trt)-OH > Fmoc-Asn(Mbh)-OH.

Multiple peptide synthesis on acid-labile handle derivatized polyethylene supports.

Using the multipin peptide synthesis approach, a range of peptides with native amide and carboxylate C-termini were generated using an acid-labile approach. Polyethylene crowns grafted with hydroxyethylmethacrylate (HEMA) polymer were functionalized with either 4-hydroxymethylphenoxyacetic acid for the generation of peptide-carboxylate or p-[(R,S)-alpha-[1-(9H-fluoren-9-yl)methoxyformamido]-2,4-dim ethoxy- benzyl]phenoxyacetic acid for peptide-amide. A range of known peptide hormone sequences and other peptides with native C-termini were assembled by sequential incorporation of N alpha-Fmoc protected amino acids. Peptides were sidechain deprotected and cleaved from crowns with TFA/scavengers within 2 mL centrifuge tubes, and isolated by a series of ether/petrol wash and centrifugation steps. In this way it was possible to avoid a cleavage and isolation botteneck, allowing rapid processing of large numbers of peptides.

Systematic study of substance P analogs. I. Evaluation of peptides synthesized by the multipin method for quantitative receptor binding assay.

The multipin peptide synthesis technique, a method for simultaneous multiple peptide synthesis, was developed for large-scale screening of oligopeptides [Geysen et al. (1984) Proc. Natl. Acad. Sci. USA, 81, 3998-4002]. A modification of the technique allows the peptides assembled on polyethylene pins to be cleaved in their native amide form and reconstituted into physiologically compatible solutions. In this study, the suitability of these peptides for quantitative receptor binding assay was evaluated. Substance P and 18 analogs, including a set of N-terminal truncated substance P and a set of naturally occurring substance P analogs, were synthesized by the multipin methods. An average yield of 20 +/- 3 nmol of peptide per pin was obtained. The purity of the peptides was estimated to be ca. 90%. The binding activities of these peptides were determined in a competition assay against 125I-BHSP binding to a rat brain synaptosome preparation. The rank order of the affinities of these peptides depicted a typical pharmacological profile of central NK1 receptor. The IC50 values obtained were also in good agreement with data reported by other groups using similar experimental conditions, except that bulk synthesized peptides were used. This study demonstrates that the peptides synthesized with the multipin technique are suitable for quantitative receptor studies, particularly for a high-volume screening of bioactive peptides.

Systematic study of substance P analogs. II. Rapid screening of 512 substance P stereoisomers for binding to NK1 receptor.

Recent developments in multiple peptide synthesis have made it feasible to synthesize and screen large numbers of peptide analogs simultaneously. We report here a model study of large scale screening of stereoisomers of substance P with systematic D-amino acid replacements. Such studies are useful in exploring conformational requirements of peptide-receptor interaction and to provide empirical information for peptide drug design. 512 stereoisomers of SP were prepared by the multipin peptide synthesis method. Receptor binding affinities of these analogs were estimated by an iterative competition assay. Results obtained form a comprehensive database on the stereochemical requirement of SP binding to central NK1 receptor. Data from analogs with single D-amino acid replacement are consistent with those previously reported showing that SP binding is highly sensitive to the chirality change of the C-terminal residues (Gln6-Leu10), but less sensitive to the chirality change of the N-terminal residues (Arg1-Gln5). A qualitative analysis of the database by comparison of series of peptide pairs revealed a repeated pattern of affinity change with D-amino acid replacement, suggesting a largely additive binding activity of SP from each residue. On the other hand, possible intramolecular interactions between some N-terminal and C-terminal residues to form an optimal binding conformation were also found. A set of 189 peptides with IC50 values less than 5 microM was subjected to an empirical QSAR analysis using a linear additive model. The relative contribution coefficients obtained agreed with the observation that the predominant contribution comes from the C-terminal residues, suggesting considerable independency of each residue on binding to NK1 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Multipin peptide synthesis at the micromole scale using 2-hydroxyethyl methacrylate grafted polyethylene supports.

The multipin peptide synthesis procedure has been adapted to allow the synthesis of peptides at micromole loadings. The original solid pin support was replaced with a detachable crown-shaped polyethylene support with an increased surface area. In addition, the polyethylene crowns were radiation-grafted with 2-hydroxyethyl methacrylate monomer instead of acrylic acid to yield hydroxy functionalized supports with a larger concentration of polymer and hence a larger peptide capacity. Fmoc-beta-Alanine was directly esterified to the HEMA hydroxy groups with subsequent addition of a diketopiperazine-forming handle for peptide attachment. Peptides varying in length from 10 to 25 residues were assembled at a number of loadings from 1.0 to 2.2 mumol. Purity of peptides at all loadings was equal to, and in some instances superior to, that achieved on conventional solid-phase supports.

Simultaneous multiple synthesis of peptide-carrier conjugates.

Recently, the multipin approach for simultaneous multiple peptide synthesis was applied to the analysis of T cell determinants by using a novel cleavage method (Maeji et al., 1990). A diketopiperazine forming linker allowed cleavage of peptides into aqueous buffer which, without further purification, could be used immediately in cell culture assays. Another potential application of the technique is the simultaneous cleavage and coupling of peptides to immunogenic carriers. Without further purification the resulting conjugates can be used for the production of antipeptide antisera. The choice of carrier and conjugation chemistry is not restricted as peptide/pin cleavage occurs in aqueous solution over a range of pH and ionic strength. The method was assessed using the 2,4-dinitrophenyl group as a model hapten, diphtheria toxoid as the carrier, and N-(epsilon-maleimidocaproyloxy)succinimide as the cross-linking reagent. The resulting DNP-DT conjugate was used to prepare high titered specific anti-DNP antisera in mice.

Synthesis of peptide analogues using the multipin peptide synthesis method.

Modification of the multipin peptide synthesis method which allows the simultaneous synthesis of large numbers of different peptide analogues is described. Peptides were assembled on polyethylene pins derivatized with a 4-(beta-alanyloxymethyl)benzoate (beta-Ala-HMB) handle. For comparative purposes, peptides were also assembled on the diketopiperazine-forming handle N epsilon-(beta-alanyl)lysylprolyloxylactate. In model studies it was demonstrated that beta-Ala-HMB-linked peptides were cleaved from polyethylene pins with dilute sodium hydroxide or 4% methylamine/water to yield analogues with beta-Ala-free acid (beta-Ala-CO2H) and beta-Ala-methylamide (beta-Ala-CONHCH3), respectively. To assess the suitability of this approach for T-cell determinant analysis, analogues of a known T-cell determinant were synthesized with the various C-terminal endings. Peptides were characterized by amino acid analysis and fast atom bombardment-mass spectrometry. HPLC of the crude cleaved peptides indicated that 22 of the 24 peptides were greater than 95% pure. These crude peptide solutions were nontoxic in sensitive cell culture assays without further purification. All three cleavage procedures gave comparable activities in T-cell proliferation assays. These results demonstrate the potential of the multipin peptide synthesis method for the production of large numbers of different peptide analogues.

Systematic screening for bioactive peptides.

Using simultaneous multiple peptide synthesis by the multipin approach, the feasibility of systematic large-scale pharmacological screening of peptide ligands was investigated. The method involves the assembly of small quantities of peptides (ca. 50 nmol) on plastic pins derivatized with an ester linker based on glycolate and 4-(hydroxymethyl)benzoate. These esters are stable under peptide synthesis and side-chain deprotection conditions but cleave under relatively mild basic conditions to generate peptides having C-terminal acid, amide and methylamide. A two-step approach to side-chain deprotection and cleavage from the solid support allows potentially toxic reagents to be removed (washed) from the peptide prior to cleavage. Consequently, the resulting peptide solutions can be used in bioassays with minimal processing. A series of angiotensin II and substance P analogs were synthesized and evaluated in an in vivo rat model and in vitro radioreceptor assay, respectively. Structure-activity studies on analogs of these bioactive peptides are well documented. The data obtained were consistent with that reported in the literature.

Multi-pin peptide synthesis strategy for T cell determinant analysis.

Techniques to synthesize many peptides simultaneously exist, however their individual cleavage and subsequent purification constitutes a bottleneck to total throughput. Biological screening of peptides is generally carried out at physiological pH in aqueous solutions. However, peptides, unless individually purified are usually contaminated by residual compounds used in their preparation such as trifluoroacetic acid, organic solvents, scavengers etc. In testing with cellular systems, such as T cell determinant analysis, such contaminations must be rigorously excluded. We have extended the pin synthesis technique of synthesizing and screening large number of peptides (Geysen et al., 1984) to the analysis of T cell determinants. Peptides can be synthesized on polyethylene pins, the side chain protective groups removed and the peptides washed free of contaminants. A linker system stable under these conditions can then be triggered to cleave the peptides from the pins in an aqueous solution at neutral pH. This strategy enables the rapid mapping of T cell determinants. It is also applicable to other systems where large numbers of solution phase peptides are required, for example, in the study of hormone analogues.