Total Solid-phase Synthesis Research Articles

Structural Revision of Natural Cyclic Depsipeptide MA026 Established by Total Synthesis and Biosynthetic Gene Cluster Analysis.

A revised structure of natural 14-mer cyclic depsipeptide MA026, isolated from Pseudomonas sp. RtlB026 in 2002 was established by physicochemical analysis with HPLC, MS/MS, and NMR and confirmed by total solid-phase synthesis. The revised structure differs from that previously reported in that two amino acid residues, assigned in error, have been replaced. Synthesized MA026 with the revised structure showed a tight junction (TJ) opening activity like that of the natural one in a cell-based TJ opening assay. Bioinformatic analysis of the putative MA026 biosynthetic gene cluster (BGC) of RtIB026 demonstrated that the stereochemistry of each amino acid residue in the revised structure can be reasonably explained. Phylogenetic analysis with xantholysin BGC indicates an exceptionally high homology (ca. 90 %) between xantholysin and MA026. The TJ opening activity of MA026 when binding to claudin-1 is a key to new avenues for transdermal administration of large hydrophilic biologics.

Total Synthesis of Analogs of A54145D and A54145A1 for Structure-Activity Relationship Studies.

The total solid-phase synthesis and in vitro biological activity of a series of analogs of A54145 factor D (A5D) and A54145 factor A1 (A5A1), two cyclic lipodepsipeptide antibiotics, are reported. An on-resin cyclization strategy was employed to prepare A5A1 analogs in which Thr4, the residue involved in the depsi (ester) bond, was replaced with either diaminopropionic acid (DAPA), (2S,3R)-diaminobutyric acid (DABA), or serine, effectively replacing the ring-closing ester bond with an amide linkage or with a primary ester. Antibacterial studies with these four analogs revealed that, contrary to a previous report, replacing the ester bond with an amide bond significantly reduces biological activity, and that both the ester bond and the methyl group at the γ-position of Thr4 are crucial for activity. Consistent with literature reports, we found that the single substitution of either 3-hydroxyasparagine (HOAsn) or 3-methoxyaspartate (MeOAsp) with Asn or Asp, respectively, in A5D is more detrimental to activity than the double substitution where both HOAsn and MeOAsp are replaced with Asn or Asp, respectively.

A convenient and efficient total solid-phase synthesis of DOTA-functionalized tumor-targeting peptides for PET imaging of cancer

IntroductionAn efficient and cost-effective synthesis of the metal chelating agents that couple to tumor-targeting peptides is required to enhance the process of preclinical research toward the clinical translation of molecular imaging agents. DOTA is one of the most widely used macrocyclic ligands for the development of new metal-based imaging and therapeutic agents owing to its ability to form stable and inert complexes under physiological conditions. Although solid-phase synthesis compatible DOTA-tris-(t-Bu ester) is a commercial product, it is expensive and contain chemical impurities. There is a need to explore new and cost-effective methods for the preparation of metal chelating agents, i.e., DOTA, directly on solid support to facilitate rapid, cost-effective, and high purity preparation of DOTA-linked peptides for imaging and therapy. In the present study, we describe a facile synthetic strategy of DOTA preparation and its linkage to peptides directly on solid-phase support.MethodsBombesin (BN) peptides were functionalized with DOTA chelator prepared from cyclen precursor on solid-phase and from commercial DOTA-tris and radiolabeled with 68Ga. In vitro BN/GRP receptor binding affinities of the corresponding radiolabeled peptides were determined by saturation binding assays on human breast MDA-MB-231, MCF7, T47D, and PC3 prostate cancer cells. Pharmacokinetics were studied in Balb/c mice and in vivo tumor targeting in MDA-MB-231 tumor-bearing nude mice.ResultsDOTA was prepared successfully from cyclen on solid-phase support, linked specifically to BN peptides and resultant DOTA-coupled peptides were radiolabeled efficiently with 68Ga. The binding affinities of all the six BN peptides were comparable and in the low nanomolar range. All 68Ga-labeled peptides showed high metabolic stability in plasma. These radiopeptides exhibited rapid pharmacokinetics in Balb/c mice with excretion mainly through the urinary system. In nude mice, MDA-MB-231 tumor uptake profiles were slightly different; the BN peptide with Ahx spacer and linked to DOTA through cyclen exhibited higher tumor uptake (2.32% ID/g at 1 h post-injection) than other radiolabeled BN peptides investigated in this study. The same leading BN peptide also displayed favorable pharmacokinetic profile in Balb/c mice. The PET images clearly visualized the MDA-MB-231 tumor.ConclusionsDOTA prepared from cyclen on solid-phase support showed comparable potency and efficiency to DOTA-tris in both in vitro and in vivo evaluation. The synthetic methodology described here allows versatile, site-specific introduction of DOTA into peptides to facilitate the development of DOTA-linked molecular imaging and therapy agents for clinical translation.

Total Solid-Phase Synthesis of Dehydroxy Fengycin Derivatives

A rapid and efficient solid-phase strategy for the synthesis of dehydroxy fengycins derivatives is described. This synthetic approach involved the linkage of a Tyr to a Wang resin via a Mitsunobu reaction and the elongation of the peptide sequence followed by subsequent acylation of the N-terminus of the resulting linear peptidyl resin, esterification of the phenol group of a Tyr with an Ile, and final macrolactamization. The amino acid composition as well as the presence of the N-terminal acyl group significantly influenced the stability of the macrolactone. Cyclic lipodepsipeptides with a l-Tyr3/d-Tyr9 configuration were more stable than those containing the Tyr residues with an opposite configuration. This work constitutes the first approach on the total solid-phase synthesis of dehydroxy fengycin derivatives.

Universal Molecular Scaffold for Facile Construction of Multivalent and Multimodal Imaging Probes

Multivalent and multimodal imaging probes are rapidly emerging as powerful chemical tools for visualizing various biochemical processes. Herein, we described a bifunctional chelator (BFC)-based scaffold that can be used to construct such promising probes concisely. Compared to other reported similar scaffolds, this new BFC scaffold demonstrated two major advantages: (1) significantly simplified synthesis due to the use of this new BFC that can serve as chelator and linker simultaneously; (2) highly efficient synthesis rendered by using either click chemistry and/or total solid-phase synthesis. In addition, the versatile utility of this molecular scaffold has been demonstrated by constructing several multivalent/multimodal imaging probes labeled with various radioisotopes, and the resulting radiotracers demonstrated substantially improved in vivo performance compared to the two individual monomeric counterparts.

Syntheses and Activity of Carbohydrate-Containing Chitinase Inhibitors

The pseudo-trisaccharide allosamidin 1 is a potent inhibitor of all family 18 chitinases, and it is confirmed to have insecticidal and antifungal activities. However, the synthesis of allosamidins is very difficult, and it is a challengeable subject. Allosamidins were synthesized in solid/liquid phase and total solid phase, respectively. Solid/liquid-phase method realizes the partial solid-phase synthesis of allosamidins. Total solid-phase method greatly simplifies the purification process. Moreover, it indicated that the inhibitory activity of N,N'-diacetyl-β-chitobiosylallosamizoline 9 against chitinase from Bombyx mori was a little weaker than that of allosamidin 1. Keywords: Allosamidins, solid/liquid-phase synthesis, total solid-phase synthesis, chitinase inhibitory activity, comparison.

A new strategy for total solid-phase synthesis of polymyxins

Polymyxin B and E are used as a ‘last line’ therapy for infections caused by serious Gram-negative bacteria due to their highly efficient antibacterial activity and nephrotoxicity. Many research groups have been performed on designing polymyxin analogues by chemical synthesis in order to decrease the nephrotoxicity and increase the antibacterial activity simultaneously. In this study, we developed a new strategy for total solid phase synthesis of polymyxins and their analogues. This method is achieved by anchoring the amine side chain of Dab9 on resin first and on-resin cyclization at last. Comparing to the mostly used chemical synthetic method for polymyxins which involves solid phase peptide synthesis followed by liquid phase cyclization, the method reported here is more convenient and efficient. Therefore, this new strategy may be a good replacement for current chemical synthetic method in designing polymyxin analogues.

Synthesis of Orthogonally Protected Muramic Acid Building Blocks for Solid Phase Peptide Synthesis

Muramic acid is found in many peptide natural products containing oligo(poly)saccharide moieties. Taking into consideration that the Fmoc methodology is routinely used for solid-phase peptide synthesis, preparation of orthogonally protected muramic acid building blocks for total solid-phase synthesis of these natural products is of particular practical importance. Herein a simple and efficient synthesis of benzyl 2-amino-4, 6-O-benzylidene-3-O-[(R)-1-carboxyethyl]-2-deoxy-N-9-fluorenylmethyloxycarbonyl-α- D -glucopyranoside (6) from N-acetylglucosamine (1) is described. Important improvements over previous synthetic approaches to glucopyranosides 2 (benzyl 2-acetamido-2-deoxy-α- D -glucopyranoside) and 3 (benzyl 2-acetamido-4, 6-O-benzylidene-2-deoxy-α- D -glucopyranoside), key building blocks in preparation of 6, include synthesis simplification and efficient isolation and purification. Optically pure (S)-2-chloropropionic acid 7 was prepared and introduced to the positon 3-O of sugar moiety to give compound 4 (benzyl 2-acetamido-4, 6-O-benzylidene-3-O-[(R)-1-carboxyethyl]-2-deoxy-α- D -glucopyranoside) with the (R)-configuration of the lactyl side-chain in excellent overall yield and optical purity. Deacetylation of amino group gave compound 5 (benzyl 2-amino-4, 6-O-benzylidene-3-O-[(R)-1-carboxyethyl]-2-deoxy-α-D-glucopyranoside) suitable for incorporation of the Fmoc protecting group to give protected muramic acid derivative 6, a useful building block in peptide synthesis.

A total solid-phase synthesis of DILP8.

We have developed a cysteine anchoring method for the synthesis of DILP8 and its analogues. The first is to synthesis of DILP8A SS13-18, C14-MeOBzl, C24-Acm and activate it as DILP8A S13-18, C14-SSPyr C24-Acm. A next step is to synthesize the DILP8BC16-Acm. The desired peptide, DILP8 with Cys(Acm) at A-24 and B-16, was then dissolved in 75% HOAc by addition of Iodine in MeOH and 4M HCl in dioxane. The reaction mixture was monitored by HPLC and the excess iodine was reduced with ascorbic acid. Purification of the peptide was achieved by HPLC. Pure synthetic DILP8 showed a single peak on analytical HPLC with corrected molecular ion. By using the above methods, enough peptide and highly homogenous pure DLP8 were generated.

Total Solid-Phase Synthesis of NOTA-Functionalized Peptides for PET Imaging

A convenient approach to functionalize peptides either at the N-terminal or on a lysine side chain with 1,4,7-triazacyclononane-N,N',N''-triacetic acid (NOTA) chelating unit has been developed on solid support. The chelate was assembled in a two-step process starting with bromo-acetylated peptides. Deprotection and cleavage of the resin-bound NOTA peptides were performed with use of trifluoroacetic acid (TFA) in the presence of thioanisole and water to give free NOTA peptides.

Chemical methods for peptide-oligonucleotide conjugate synthesis.

Methods of peptide-oligonucleotide conjugate synthesis are presented that may be useful in the study of cell targeting and delivery of oligonucleotides and their analogs. The first method involves total stepwise solid-phase synthesis on a single support. The second involves preparation of oligonucleotides containing 2'-aldehydes and subsequent chemoselective ligation with functionalized peptides to form hydrazine, oxime, or thiazolidine linkages.

A Combination of Different Spectroscopic Techniques to Monitor the “in situ” Solid‐phase Synthesis of Organic Molecules

AbstractThe efficacy, limitations and scope of different spectroscopic techniques to monitor solid‐phase syntheses are discussed. The total solid‐phase synthesis of a natural product derivative, 3,17‐di‐O‐acetyllamellarin U, has been monitored by gel‐phase NMR and HR‐MAS NMR as appropriate. FT‐IR and colorimetric tests also proved to be valuable tools for monitoring the progress of reactions. While the data obtained by FT‐IR provided valuable information on some functional groups, the NMR data provided more specific structural information that allowed the progress of reactions to be monitored. After several reaction steps the “aging” of the resin only allowed the product covalently anchored to the resin to be investigated using an HR‐MAS probe, a situation that severely limited the depth of analysis available.

Cystine mimetics––solid phase lanthionine synthesis

The total solid phase synthesis of an analogue of the B ring of nisin was achieved, in a biomimetic fashion, via the solid phase diastereoselective cyclisation of a dehydrothiol-containing peptide.

Total Stepwise Solid-Phase Peptide-Oligonucleotide Conjugate Synthesis on Macroporous Polystyrene

An efficient total stepwise solid-phase synthesis of oligonucleotide-peptide conjugates on a macroporous polystyrene is described. Extending our homoserine linker approach, we prepared a range of fluorescein-labelled conjugates containing one of two different peptides together with oligonucleotides containing 2′-deoxynucleoside or 2′-O-methylribonucleoside phosphodiesters, or gapmers containing 2′-deoxyphosphorothioate sequences flanked by 2′-O-methyl wings.

Solid-phase total synthesis of the pentacyclic system lamellarins U and L.

[reaction: see text] A total solid-phase synthesis of lamellarins U and L has been achieved. The conversion of an aldehyde group into a formate by a Baeyer-Villiger reaction and a intramolecular [3 + 2] cycloaddition of a 3,4-dihydroisoquinolinium salt over a triple bond comprise the key steps of the process. Each transformation has been controlled with the proper spectroscopic and analytical methods.

Synthesis of Lanthionine‐Containing Peptides on Solid‐Phase via an Orthogonal Protecting Group Strategy

AbstractFor Abstract see ChemInform Abstract in Full Text.

Tentoxin as a scaffold for drug discovery. Total solid-phase synthesis of tentoxin and a library of analogues.

[reaction: see text] A solid-phase method for the synthesis of tentoxin has been developed. Two key steps-dehydration and N-alkylation-are carried out while the peptide is anchored to the resin. The method, which has been validated by the preparation of a library of tentoxin analogues, should be applicable to the generation of further libraries that have the tentoxin scaffold structure, as well as other structures containing N-alkylated didehydroamino acids.

Synthesis of peptide-oligonucleotide conjugates: application to basic peptides.

Efficient methods of synthesis of peptide-oligonucleotide conjugates are badly needed for studies of uptake into cells in culture. We describe improvements to the procedures involved in "native ligation" conjugation in solution to extend the method to basic peptides. Further, we describe progress in development of a total solid-phase synthesis approach that makes use of a L-homoserine linker as the key reagent for growing of oligonucleotide and peptide chains on a single solid support.

Total Solid Phase Synthesis of the Biologically Active Peptaibol Antibiotic Zervamicin IIB

Total Solid Phase Synthesis of the Biologically Active Peptaibol Antibiotic Zervamicin IIB

Solid-phase synthesis, isolation and analysis of a mouse protein, the macrophage migration inhibitory factor

Murine macrophage migration inhibitory factor (mMIF) is an Mr 12 500 protein composed of all natural amino acid residues. Using the fluorenylmethoxycarbonyl chemistry for solid-phase peptide synthesis (SPPS) under special conditions, a stepwise approach was very successful leading to a crude product in unexpected high purity. After RP-HPLC isolation, a little mass difference of −12 u was determined for the received protein by matrix-assisted laser desorption ionization MS and ion spray MS and the failure sequence [Ser15]-mMIF identified by Edman degradation. The total solid-phase synthesis was repeated in the stepwise manner under the same conditions leading to the expected mMIF protein in high purity, which was confirmed by different analytical methods. Our results shows the reproducibility of our SPPS approaches to proteins and point out the importance of high-resolution mass spectrometry for a rapid and accurate analysis of such biopolymers.