Synthesis of guanidinium-derived receptor libraries and screening for selective peptide receptors in water

A library of "tweezer" receptors, incorporating a guanidinium "head group" and two peptide derived side arms has been prepared on the solid-phase using an orthogonally protected guanidinium scaffold 12. The library was screened with various tripeptide derivatives in an aqueous solvent system. A tweezer receptor 25 for the side chain protected tripeptide 19 was identified from the screening experiments. Receptor 25 was resynthesised and solution binding studies were carried out, which revealed that 25 binds to tripeptide 19 with K(a)=8.2 x 10(4) +/- 2.5 x 10(4) (15 % DMSO/H(2)O, pH 8.75) and with appreciable selectivity over the tripeptide enantiomer 22 and the side chain deprotected tripeptide 20.     

Peptide bond formation catalyzed by α-chymotrypsin in ionic liquids

α-Chymotrypsin catalyzed peptide bond formation was studied in ionic liquids using the synthesis of a protected fragment of Leu-enkephalin, ZTyrGlyGlyOEt, as model reaction. MOEMIM·PF₆ was found to be the most favorable solvent among the six different 1-alkyl-3-methylimidazolium hexafluorophosphates and tetrafluoroborates ionic liquids screened. With MOEMIM·PF₆ as reaction media, several di- or tripeptide derivatives were successfully prepared in 68-75% isolated yields.     

Synthesis of Taiwan Cobra Venom Cardiotoxin II Synthesis of Protected Hexapeptide,Sequence 44-49 and Protected Tripeptide,Sequence 50-52

The protected hexapeptide (sequence 44-49) and the protected tripeptide (sequence 50-52) of Taiwan Cobra (Naja naja atra) venom cardiotoxin were synthesized by stepwise coupling and fragment coupling methods. The protected hexapeptide is Nps-Lys(Z)-Ser-Ser-Leu-VaI-Leu-OMe and the protected tripeptides are Nps-Lys(Z)-Tyr(Bzl)-Val-OMe and Boc-Lys(Z)-Tyr(Bzl)-VaI-OMe.     

Chemical ligation of S-scylated cysteine peptides to form native peptides via 5-, 11-, and 14-membered cyclic transition states

Cysteine-containing dipeptides 3a-l, (3b+3b') (compound numbers in parentheses are used to indicate racemic mixtures; thus (3b+3b') is the racemate of 3b and 3b'), and tripeptide 13 were synthesized in 68-96% yields by acylation of cysteine with N-(Pg-α-aminoacyl)- and N-(Pg-α-dipeptidoyl)benzotriazoles (where Pg stands for protecting group in the nomenclature for peptides throughout the paper) in the presence of Et(3)N. Cysteine-containing peptides 3a-l and 13 were S-acylated to give S-(Pg-α-aminoacyl)dipeptides 5a-l and S-(Pg-α-aminoacyl)tripeptide 14 without racemization in 47-90% yields using N-(Pg-α-aminoacyl)benzotriazoles 2 in CH(3)CN-H(2)O (7:3) in the presence of KHCO(3). (In our peptide nomenclature, the prefixes di-, tri-, etc. refer to the number of amino acid residues in the main peptide chain; amino acid residues attached to sulfur are designated as S-acyl peptides. Thus we avoid use of the prefix "iso".) Selective S-acylations of serine peptide 3k and threonine peptide 3l containing free OH groups were thus achieved in 58% and 72% yield, respectively. S-(Pg-α-aminoacyl)cysteines 4a,b underwent native chemical ligations to form native dipeptides 3f,i via 5-membered cyclic transition states. Microwave irradiation of S-(Pg-α-aminoacyl)tripeptide 15 and S-(Pg-α-aminoacyl)tetrapeptide 17 in the presence of NaH(2)PO(4)/Na(2)HPO(4) buffer solution at pH 7.8 achieved chemical ligations, involving intramolecular migrations of acyl groups, via 11- and 14-membered cyclic transition states from the S-atom of a cysteine residue to a peptide terminal amino group to form native peptides 19 and 20 in isolated yields of 26% and 23%, respectively.     

Conformational heterogeneity of tripeptides containing Boc-Leu-Aib as corner residues in the solid state

A critical analysis of single crystal X-ray diffraction studies on a series of terminally protected tripeptides containing a centrally positioned Aib (α-aminoisobutyric acid) residue has been reported. For the tripeptide series containing Boc-Ala-Aib as corner residues, all the reported peptides formed distorted type II β-turn structures. Moreover, a series of Phe substituted analogues (tripeptides with Boc-Phe-Aib) have also shown different β-turn conformations. However, the Leu-modified analogues (tripeptides with Boc-Leu-Aib) disrupt the concept of β-turn formation and adopt various conformations in the solid state. X-ray crystallography sheds some light on the conformational heterogeneity at atomic resolution.     

Syntheses of thyrotropin-releasing hormones (TRH) (Schaf) and related peptides

The syntheses of seven tripeptide isomers containing L -histidine, L -proline and L -glutamic acid residues, the same as found in the natural thyrotropin-releasing hormone (TRH), are reported. In addition L -pyroglutamyl-L -histidyl-L -proline and its amide as well as N^α-acetyl-L -glutamyl-L -histidyl-L -proline are described. Whereas eight peptides are inactive and L -pyroglutamyl-L -histidyl-L -proline shows a slight TRH activity, L -pyroglutamyl-L -histidyl-L -proline-amide has the full biological activity of the isolated thyrotropin-releasing hormone and, at the present state of knowledge, seems to be identical with it.     

Total Enzymatic Synthesis of the Cholecystokinin Octapeptide (CCK‐8)

The enzymatic synthesis of the cholecystokinin octapeptide (CCK‐8) is reported. The target octapeptide CCK‐8 is the minimum active sequence with the same biological activity as naturally occurring cholecystokinin and is a potential therapeutic agent in the control of gastrointestinal function as well as a drug candidate for the treatment of epilepsy and obesity. The protected CCK‐8 was obtained by incubation of Bz‐Arg‐Asp(OEt)‐Tyr‐Met‐OAl and Gly‐Trp‐Met‐Asp(OMe)‐Phe‐NH₂ with immobilized α‐chymotrypsin. The Bz‐Arg group was used as an N‐terminal protecting group in the synthesis of the tripeptide fragment. The protected CCK‐8 was treated with trypsin to remove the Bz‐Arg group successfully. Free or immobilized enzymes were used as catalysts. The effect of the acyl donor ester structure, the C(α) protecting group of the nucleophile, reaction media, enzyme, and the carrier of the enzymes on the outcome of the coupling reaction was studied.     

Angiotensin II Analogues. Part II. Synthesis and incorporation of the sulfur-containing aromatic amino acids: L-(4′-SH)Phe,L-(4′-SO2NH2)Phe,L-(4′-SO)Phe and L-(4′-S-CH3)Phe

L -Phenylalanine has been treated with chlorosulfonic acid and the product was either hydrolyzed, ammonolyzed or reduced. The resulting sulfonic-acid and aminosulfonyl derivatives have been employed for peptide synthesis with Boc-protection of the N^α-position only. The reduction product L -(4′-SH)Phe has been protected by formation of asymmetric disulfides or with various thiol protecting groups (benzyl-, methyl- and acetamidomethyl groups, the latter being the most suitable for peptide synthesis). With these protected amino acids several analogues of angiotensin II have been synthesized by the solid-phase method. These analogues have been used for structure-activity relationship studies on three different bioassays.     

Penicillin biosynthesis the immediate origin of the sulphur atom

A mixture of tripeptide isotopomers δ-(L-α-aminoadipyl)-L-cystelnyl-D [2-²H]-valine and δ-(L-α-aminoadipyl)-L-(³⁴S-cysteinyl)-D-valine were converted by the enzyme isopenicillin-N-synthetase into isopenicillin N. The distribution of the ²H and ³⁴S in this product, determined by mass spectrometry, showed there was no transfer of the sulphur between the precursor molecules during conversion to penicillin.     

α-Cétoaldéhydes à groupement aldéhydique ou cétonique protégé

α-Ketoaldehydes with protected ketogroup 2 or protected aldehydrogroup 3 are obtained by reaction of thiophenol or methanol with α-chloro-α-(phenylthio)aldehydes 7.     

全保护RGD三肽的合成方法研究

以两条路线、多种偶联试剂(DCC，EDCI，CDI，EEDQ)合成了全保护三肽Arg- Gly-Asp(RGD)．Boc-Arg(Tos)-OH经上述偶联剂短时活化，于合适条件下与Ts0H- G1y-OBzl缩合，均获得良好收率(43％-97％)．经Pd(OH)2／H2还原得到的Boc-Arg (Tos)-G1y-0H于22-27℃与HCl·Asp(OcHex)-OBzl偶联得到全保护三肽Boc-Arg (Tos)-Gly-Asp(OcHex)-OBzl(TM)，反应收率分别为76．4％(DCC／HOSu)，64．7％ -78．3％(DCC／HOBt)，66．7％-77．9％(EDCI／HOBt)．Boc-Gly-OH和HCl·Asp- (OcHex)-OBzl经DCC／HOBt或CDI活化，可得到碳端二肽Boc-Gly-Asp(OcHex)-OBzl (收率分别为81．2％，89．5％)，该二肽脱Boc后与Boc-Asp(Tos)-OH反应，经DCC ／HOBt，EDCI／HOBt，CDI，DCC／HOSu活化，均可生成目标分子TM，其反应收率分 别为40．4％，73．8％，67．8％，84．4％．     

Synthesis of a tripeptide derivative containing the gln-arg hydroxyethylene dipeptide isostere

[structure: see text] The protected hydroxyethylene dipeptide isostere of Gln-Arg and the tripeptide derivative 1 were synthesized as components of potential peptidase inhibitors.     

Giant macrolactams based on β-sheet peptides

This paper reports the use of natural amino acids, the tripeptide β-strand mimic Hao, and the β-turn mimic δ-linked ornithine to generate water-soluble 54-, 78-, and 102-membered-ring macrolactams. These giant macrocycles were efficiently prepared by synthesis of the corresponding protected linear peptides, followed by solution-phase cyclization and deprotection. The protected linear peptide precursors were synthesized on 2-chlorotrityl chloride resin by conventional Fmoc-based solid-phase peptide synthesis. Macrocyclization was typically performed using HCTU and N,N-diisopropylethylamine in DMF at ca. 0.5 mM concentration. The macrocycles were isolated in 13-45% overall yield after HPLC purification and lyophilization. 1D, 2D TOCSY, and 2D ROESY (1)H NMR studies of the 54- and 78-membered-ring macrolactams establish that these compounds fold to form β-sheet structures in aqueous solutions.     

From cyclic dehydrodipeptides to uncommon acyclic peptide mimetics

1-Acetyl-3-arylmethylene-2,5-piperazinediones gave N-3-arylpyruvylamino esters by acid-promoted alcoholysis under thermal conditions or microwave irradiation. Compounds obtained from 1-acetyl-3-(o-nitro)arylmethylene-2,5-piperazinediones gave, after reduction of the nitro group and spontaneous cyclization, N-2-indolylcarbonylamino acid derivatives. A similar alcoholysis/reduction sequence applied to dehydrodipeptides bearing a 3(4)-nitroaryl substituent gave N-3(4)-aminophenyl-α-ketopropionylamino acid derivatives. Coupling of the free amino group with Boc-protected amino acids gave tripeptide mimetics with a 6-aminoindole-2-carboxylic or a 3(4)-aminophenyl-α-ketopropionic acid as the second residue.     

Synthesis of terminally protected (S)-β3-H-DOPA by Arndt–Eistert homologation: an approach to crowned β-peptides

Terminally protected Boc-(S)-β³-H-DOPA-OMe has been synthesized from l-DOPA by the Arndt–Eistert homologation procedure. During the synthesis, the side-chain catechol group was temporarily protected by benzylation. The absence of racemization was demonstrated by ¹⁹F NMR analysis of the (+)-(R)- and (−)-(S)-α-methoxy-α-trifluoromethyl-α-phenyl-acetamide derivatives. The catechol function of Boc-(S)-β³-H-DOPA-OMe may be used for crown-ether formation, a step towards the construction of crowned β-peptides.     

Kinetics and mechanism of the decomposition of N,N-dihalopeptides

The tripeptide alanylalanylalanine reacts with either HOCl or HOBr to form a N,N-dihalopeptide. These compounds decompose to the N-halo-N′-(α-iminoketo)peptides plus halide ion. The rate constants for these reactions in 0.4-M NaCl were determined to be where the activation energies are in cal/mol. The N-halo-N′-(α-iminoketo)-peptides slowly decompose either by a two-step hydrolysis reaction to form ammonia, halide ion, and an N-(α-acylketo)peptide, or by direct decomposition to a nitrile, an isocyanopeptide, and a halide ion.     

The synthesis of a geminally perfluoro-tert-butylated beta-amino acid and its protected forms as a potential pharmacokinetic modulator and reporter for peptide-based pharmaceuticals

To modulate and report the pharmacokinetics of peptide-based pharmaceuticals, a novel geminally perfluoro-tert-butylated beta-amino acid (betaFa) and its Fmoc- and Boc-protected forms were designed and synthesized. betaFa was incorporated into a model tripeptide via standard solid-phase chemistry. Both the amino acid (free and protected) and the tripeptide show a sharp singlet 19F NMR signal. Reversed-phase chromatography and 1-octanol/water partition measurements demonstrate that betaFa is extremely hydrophobic.     

Solid-phase synthesis and spectroscopic studies of TRH analogues incorporating cis- and trans-4-hydroxy-L-proline.

An efficient solid-phase synthesis of the TRH analogue Glp-His(Nim-Trt)-Hyp-OH is described. Na-Fmoc protected amino acids and DCC/HOBt activation were employed. The bulky and mild-acid-sensitive 2-chlorotrityl resin, utilised as the solid support, completely suppressed dioxopiperazine formation. The tripeptide is a key intermediate in the synthesis of TRH analogues incorporating cis- and trans-4-hydroxy-L-proline. The tripeptide was converted, with inversion of configuration at C-4 of the Hyp residue, to Glp-His(Nim-Trt)-cHyp lactone in the presence of triphenylphosphine-diethyl azodicarboxylate (TPP-DEAD). One-pot MeOH-TPP-DEAD transesterification of the lactone, followed by Nim-detritylation, provided Glp-His-cHyp-OMe. This ester gave the corresponding amide and acid on ammonolysis and saponification, respectively. A high-field 1H NMR investigation of Glp-His-cHyp-OH and its diastereomer Glp-His-Hyp-OH, obtained by Nim-detritylation of the key tripeptide, showed that the configuration at C-4 of the prolyl residues is critical for the determination of the preferred three-dimensional structure of the molecules.     

Protease-catalyzed Synthesis of Bz-Arg-Gly-Asp-OMe in Full Aqueous Medium

Synthesis of N-benzoyl-argininylglycylasparagine methyl ester(Bz-Arg-Gly-Asp-OMe),a precursor tripeptide of Arg-Gly-Asp)was catalyzed by papain under kinetic control,at alkaline pH,in a full aqueous medium.The substrates were N-benzoyl-argininylglycine ethyl ester and asparagine dimethyl ester.An aqueous solution of 0.1 mol/L KCl/NaOH containing 8 mmol/L EDTA and 2 mmol/L DTT was selected as the reaction medium.The synthesized hydrophilic tripeptide was soluble in the reaction medium during the reaction process,however,the secondary hydro-lysis of the tripeptide product was not considerable.The effects of different factors,including water content,temperature,reaction time,and molar ratio of the substrates,on the yield of Bz-Arg-Gly-Asp-OMe were examined.The optimal reaction conditions were 0.05 mol/L Bz-Arg-Gly-OEt and 0.15 mol/L Asp(-OMe)2·HCl in 0.1 mol/L KCl/NaOH solution(pH 8.5),at 40 ℃,and a reaction time of 60 min,with a maximum conversion yield of 62.4%.     

Penicillin biosynthesis: Retention of configuration at c-3 of valine during its incorporation into the arnstein tripeptide

[3-³H]-valine was efficiently synthesised from sodium α-ketoisovalerate. With a β-lactam negative mutant of C. acremonium, l-[1-¹⁴C-3-³H]-valine and dl-[1-¹⁴C-3-³H]-valine were independently incorporated into the Arnstein tripeptide dimer, i.e. Bis-δ-(l-α-aminodipyl)-l-cystinyl-bis-d-valine, with full retention of trieium at C-3 of the d-valine residue. This result strongly suggested retention of configuration at C-3 of valine when the tripeptide was biosynthesised, and further limited the number of possible mechanisms for the biosynthesis of penicillins.