Synthetic derivatives and analogues of γ-L-glutamyl-taurine,a bioactive compound from bovine parathyroids

γ-L-Glutamyl derivatives and a β-L-aspartyl derivative of different amines (taurine, nortaurine, N-methyltaurine, taurine amide, tauryl-methylamine, tauryl-piperidine, β-alanine amide, orthanilic acid, 2-aminoethanephosphonic acid, ethanolamine-O-sulfate and ethanolamine-O-phosphate) have been synthesized by mixed anhydride or active ester coupling method. One of the dipeptide analogues, γ-L-glutamyl-(ethanolamine-O-sulfate) was prepared by esterification, too. Syntheses of α,γ-L-glutamyl-bis-taurine and of DL-2-amino-8-sulfo-octanoic acid are also described.     

Synthesis and in vitro anti-HIV Activity of Certain 2-(1H-Benzimidazol-2-ylamino)pyrimidin-4(3H)-ones and Related Derivatives

In an ongoing effort to develop novel non-nucleoside human immunodeficiency virus inhibitors, a series of substituted 2-(1H-benzimidazol-2-ylamino)pyrimidin-4(3H)-ones and related derivatives were synthesized via cyclocondensation of 2-guanidino-1H-benzimidazole with diethyl ethoxymethylenemalonate, substituted diethyl malonates, some β-keto esters and 2-acetylbutyrolactone. From these series of compounds, 2-(1H-benzimidazol-2-ylamino)-6-hydroxy-5-phenylpyrimidin-4(3H)-ones ( 5f , NSC 666286) was confirmed to have a moderate in vitro anti-HIV activity.     

Synthesis of N-(4-aminobenzoyl)-γ-oligo (L-glutamic acid)s*

N-(4-aminobenzoyl)-γ-oligo (l -glutamic acid)s (6) containing from two to six glutamic residues have been prepared in solution using Nα-Boc-α-Bzl protections and isobutyl-chlorocarbonate activation. Key steps in the synthesis were the coupling of γ-oligo(α-benzyl l -glutamate) benzyl esters (1) with N-(4-benzyl-oxycarbonylaminobenzoyl)-l -glutamic acid α-benzyl ester (4) to blocked precursors of N-(4-aminobenzoyl)-γ-oligo (l -glutamic acid)s (5) and catalytic hydrogenolysis of 5 to 6. Elaboration of the required oligo γ-l -glutamate chains (1) was achieved step by step beginning with the coupling of glutamic acid dibenzylester with N-(t-butoxycarbonyl)-l -glutamic acid α-benzyl ester (2) to 3 followed by selective removal of the Boc from 3 with HCl-dioxane followed by coupling with 2.     

Synthesis of enantiopure non‐natural α‐amino acids using tert‐butyl (2S)‐2‐[bis‐(tert‐butoxycarbonyl)amino]‐5‐oxopentanoate as key‐intermediate:the first synthesis of(S)‐2‐amino‐oleic acid

Abstract: A general method for the synthesis of enantiopure non‐natural α‐amino acids is described. The key intermediate tert‐butyl (2S)‐2‐[bis(tert‐butoxycarbonyl)amino]‐5‐oxopentanoate was obtained from l ‐glutamic acid after suitable protection and selective reduction of the γ‐methyl ester group by DIBALH. Wittig reaction of this chiral aldehyde with various ylides led to a variety of δ,ε‐unsaturated α‐amino acids. This methodology was applied to the synthesis of (S)‐2‐amino‐oleic acid.     

Synthesis of New 2-{[(Phenoxy or Phenyl)acetyl]amino}benzoic Acid Derivatives as 3α-Hydroxysteroid Dehydrogenase Inhibitors and Potential Antiinflammatory Agents

A number of 2-{[(phenoxy or phenyl)acetyl]amino}benzoic acid derivatives were prepared in about 50% yield from (phenoxy or phenyl)acetyl chloride and anthranilic acid derivatives. All the compounds were tested as in vitro inhibitors of 3α-hydroxysteroid dehydrogenase, since enzyme inhibition predicts potential antiinflammatory activity in vivo The most active compounds 3 1, m, s are about 3.5 times more active than acetylsalicylic acid (ASA). Activity is influenced by electronic as well as steric effects.     

3-(ω-Aminoalkyl)-5,5-dialkyl(or spirocycloalkyl-1′,5-)hydantoins as New 5-HT1A and 5-HT2A Receptor Ligands

A series of new 3-(ω-aminoalkyl)-5,5-disubstituted hydantoins, containing 1-phenylpiperazine, 1-(o-methoxyphenyl)piperazine or 1,2,3,4-tetrahydroisoquinoline fragments, were synthesized by standard alkylation procedures and their 5-HT_1A and 5-HT_2A receptor affinities were determined. It has been shown that the investigated derivatives are recognized by 5-HT_1A and 5-HT_2A receptors due to the presence of a 1-arylpiperazine fragment; however, the terminal hydantoin moiety plays an important role in stabilization of the receptor-ligand complex. It has also been found that the two 1-phenylpiperazine derivatives 32 and 36 are new, selective 5-HT_2A receptor ligands (K_i = 34 and 37 nM, respectively), whereas the derivative of 1-(o-methoxyphenyl)piperazine ( 38 ) is a new, highly potent 5-HT_1A receptor ligand (K_i = 0.51 nM) with a moderate affinity for 5-HT_2A receptors (K_i = 213 nM).     

3-NITRO-2-PYRIDINESULFENYL (Npys) GROUP

The novel 3-nitro-2-pyridinesulfenyl (Npys) group, which is useful for the protection and the activation of amino and hydroxyl groups for peptide synthesis, is reported. The Npys group is readily introduced by treatment of amino acids with 3-nitro-2-pyridinesulfenyl chloride. The Npys group is easily removed by treatment with very dilute HCl, e.g. 0.1-0.2 N HCl in dioxane, but it is resistant to trifluoroacetic acid and 88% formic acid. Npys is also selectively removed under neutral conditions using triphenylphosphine or 2-pyridinethiol 1-oxide without affecting benzyloxycarbonyl (Z), tert-butyloxycarbonyl (Boc), 2-(4-biphenylyl) propyl(2) oxycarbonyl (Bpoc), 9-fluorenylmethyloxycarbonyl (Fmoc), benzyl (Bzl) or tert-butyl (tBu) protecting groups. The N-Npys and O-Npys groups when activated in the presence of RCOOH by the addition of tertiary phosphine form peptide or ester bonds via oxidation-reduction condensation. The important features of the Npys group are demonstrated through the synthesis of peptides in solution and by solid phase methodology without a formal deprotection procedure. In solid phase synthesis, 4-(Npys-oxymethyl) phenylacetic acid is used as the key intermediate for the introduction of the trifluoroacetic acid resistant 4-(oxymethyl) phenylacetamido linking group to the resin.     

Practical preparation and deblocking conditions for N-α-(2-(P-biphenylyl)-2-propyloxycarbonyl)-amino acid (N-α-Bpoc-Xxx-OH) derivatives

Reproducible preparations are given for salts of the following L-amino acid derivatives: Bpoc-Ala-OH, Bpoc-Arg(Mtr)-OH, Bpoc-Asn-OH, Bpoc-Asp(OtBu)-OH, Bpoc-Cys(Acm)-OH, Bpoc-Cys(S-tBu)-OH, Bpoc-Gln-OH, Bpoc-Glu(OtBu)-OH, Bpoc-Gly-OH, Bpoc-Ile-OH, Bpoc-Leu-OH, N-α-Bpoc-Lys(ε-Boc)-OH, Bpoc-Met-OH, Bpoc-Phe-OH, Bpoc-Pro-OH, Bpoc-Ser(OtBu)-OH, Bpoc-Thr(OtBu)-OH, Bpoc-Tyr-OH, Bpoc-Val-OH. A study of the deblocking of N-α-Bpoc peptides in dichloromethane containing 0.5% trifluoroacetic acid revealed that a rapid equilb-rium is established between the first-formed monomeric alkene 2-p-biphenylylpropene and the hindered dimer 2,4-bis(p-biphenylyl)-4-methyl-l-pentene. Thioethers were found to be inefficient carbocation scavengers for the deblocking reaction. The most efficient scavengers were found to be thiophenol and benzyl mercaptan, and the following approximate reactivity order was established: benzyl mercaptan ～ thiophenol 〉 indole 1,3-dimethoxybenzene ～ resorcinol 〉1,3,5-trimethoxybenzene ～ dimethyl sulfide ～ thioanisole.     

The preferred solid-state conformation of (αMe)Trp peptides

The two Z-l -Ala-d l -(xMe)Trp-NH₂ diastereomeric dipeptides were synthesized from (Z-l -Ala)₂O and H-dl -(xMe)Trp-NH₂. The latter racemate, prepared by phase-transfer catalyzed alkylation of the N^α-benzylidene derivative of alanine amide followed by acidic hydrolysis of the resulting Schiff base, was characterized by X-ray diffraction. The molecular and crystal structure of Z-l -Ala-l -(αMe)Trp-NH², separated from its diastereomer by silica-gel column chromatography, was determined by X-ray diffraction analysis. Both independent molecules in the asymmetric unit of the dipeptide adopt a type-II β-bend conformation. However, only the more regularly folded conformation of molecule B is stabilized by a 1←4 C=O…H—N intramolecular H bond. The present results indicate that: (i) the Cα-methylated (αMe)Trp residue is a strong β-bend and helix former, and (ii) the relationship between (αMe)Trp chirality and helix screw sense tends to be opposite to that of protein amino acids. The implications for the use of the (αMe)Trp residue in designing conformationally restricted analogs of bioactive peptides are briefly discussed. ©Munksgaard 1995.     

Solid phase synthesis of peptides containing the non-hydrolysable analog of (O)phosphotyrosine,P(CH2PO3H2)Phe

Studies about phosphorylation-dephosphorylation mechanisms require the development of probes capable of being used in in vitro and in vivo conditions. We show in this work that the chemically and enzymatically stable p(CH₂PO₃H₂) Phe analog of (O)phosphotyrosine can be easily introduced in peptides by the solid-phase method. It has been incorporated in the 344-357 sequence of the β₂ adrenergic receptor in place of the Tyr residue in position 350 and/or 354 in order to investigate the role of tyrosine phosphorylation in the receptor agonist-induced down-regulation. Since p(CH₂PO₃H₂)Phe is an ionized hydrophilic residue, peptides containing this amino acid do not easily permeate the cellular membranes. Therefore the modified amino acid was introduced in the synthetic pathway in its N-Boc- p (CH₂PO₃Et₂)Phe form, which could be partially or completely deprotected. Coupling steps, including that of the new amino acid, were performed with good yields (~60% total yield) and further deprotections provided both the p(CH₂PO₃H₂)Phe and p(CH₂PO₃HEt)Phe containing peptides with yields of around 20% each. The structure of the peptides was assessed by NMR, mass spectroscopy and amino acid analysis and the new amino acid was characterized under its phenyl-thiocarbamyl form (PTC).     

Synthesis and bioassay of LHRH-antagonists with N-Ac-d-O-phenyltyrosine and N-Ac-d-3-(2-dibenzofuranyl)alanine in position 1

N-Ac-d -O-phenyltyrosine was synthesized via the corresponding azlactone. Resolution of the dl methyl esters was achieved by Subtilisin Carlsberg. Treatment with palladium(II) acetate in trifluoroacetic acid converted N-Ac-d -O-phenyltyrosine into N-Ac-d -3-(2-dibenzofuranyl)alanine. These two amino acids were incorporated instead of N-Ac-d -2-Nal into position 1 of the LHRH-antagonist (N-Ac-d -2-Nal¹, d -pClPhe², d -3-Pal³, c-PzACAla⁵, d -PiCLyS⁶, ILys⁸,d -Ala¹⁰)-LHRH. The more rigid N-Ac-d -3-(2-dibenzofuranyl)alanine was structurally more effective than N-Ac-d -O-phenyltyrosine; the AOAs for the corresponding analogs were 82 and 38%, respectively, at 0.5 μg. Replacement of c-PzACAla in position 5 by O-phenyltyrosine significantly decreased potency.     

A convenient general method for synthesis of Nα- or Nω-dithiasuccinoyl (Dts) amino acids and dipeptides: application of polyethylene glycol as a carrier for functional purification*

N ^α-Dithiasuccinoyl (Dts) amino acids ( 1 ) needed for solid-phase peptide synthesis have been prepared in good yields and excellent purities by a new method that exploits the solubility properties of polyethylene glycol (PEG; bifunctional with average molecular weight 2000 was found to be optimal). Suitably side-chain protected amino acid derivatives are first reacted with a polymeric xanthate ( 11 ), following which the free α-carboxyl is blocked by silylation and the Dts heterocycle is elaborated in the same pot by reaction with chlorocarbonylsulfenyl chloride ( 4 ). Upon aqueous workup, the polymeric carrier removes any urethane blocked amino acids which arise during the process. Exaggerated conditions were explored to prove the power of this functional purification approach, and mechanisms of formation of polymer-bound urethanes are proposed and supported by solution model studies. The preparation and characterization of the companion N-(iso-propyldithio)carbonyl derivative of proline is also presented.     

Peptidic p-nitroanilide substrates of interleukin-1β-converting enzyme

Peptidic p-nitroanilides are useful colorimetric substrates for enzymes. With the aim of developing a convenient, quantitative assay for inhibitors of interleukin-1β-converting enzyme (ICE), we have explored three approaches to the synthesis of peptidic p-nitroanilides relevant to this enzyme. The first approach involved a late stage oxidation of a p-aminoanilide such as CbzValAlaAsp(β-tert-butyl)-p-(t-Boc-amino)anilide. The second and third approaches used the preformed amino acid p-nitroanilides HAsp-p-nitroanilide hydrochloride and HAsp(7beta;-tert-butyl)-p-nitroanilide which were coupled iteratively with preactivated amino acid derivatives or with an appropriate peptide, respectively. While each approach had it merits and limitations, all three produced p-nitroanilides that were substrates for ICE.     

AMINONITRILES AND AMINOTHIOAMIDES RELATED TO NATURAL AMINO ACIDS

N-p-Methoxybenzyloxycarbonyl and N-tert.-butyloxycarbonyl amino acid amides related to a series of natural amino acids were dehydrated to the corresponding Meoz- and Boc-α-aminonitriles. Deprotection of the latter derivatives afforded α-aminonitriles related to alanine, tyrosine, phenylalanine, dihydrophenylalanine, histidine, Dopa, ornithine, asparagine and glutamine. Thioamidation with H₂S/NH₃ or H₂S/NEt₃ in general converted the protected amino nitriles to Meoz- and Boc-α-aminothioamides. When deprotected these furnished the α-aminothioamides corresponding to alanine, tyrosine, phenylalanine, dihydrophenylalanine and histidine. For dehydration and thioamidation of histidine and Dopa, Nα-Boc-^im trityl-histidine and N-Boc-0, 0′-diacetyldihydroxyphenylalanine were useful. Dopa was obtained as the free and Boc-thiohydrazide. Also prepared were Nα,ω -diMeoz-ornithine DCHA, Meoz-2,5-dihydrophenylalanine DCHA and N,0-diMeoz-tyrosine as starting materials and N,0-dicarbobenzyloxycarbonyltyrosinamide, N,0-diZ-tyrosine nitrile and Z-β-cyano-β-alaninamide as model compounds. During deprotection of Meoz-alanine thioamide, transfer of an anisyl group from the N-Meoz protecting group to sulfur took place as a side reaction that yielded alanine p-methoxybenzyl β-imidothiolic ester. This study provides two new series of amino acid analogs with potential antimetabolite activity. Also suitable for incorporation into peptide analogs, these afford approaches to relating structure and conformation to activity in biologically active peptides.     

Convenient preparation of [Orn(Tfa)2]- and [Orn(Boc)2, Orn(Tfa)2′]gramicidin S,versatile unsymmetrically protected derivatives of gramicidin S

Abstract: Treatment of gramicidin S (GS) with trifluoroacetic anhydride afforded a derivative in which only one of the two Orn side chains was trifluoroacetylated in 72% yield, furnishing the first efficient method for the preparation of a monoprotected derivative of GS. The mono(Tfa) derivative [Orn(Tfa)²]GS was treated with di-tert-butyl dicarbonate to yield dually protected derivative [Orn(Boc)²,Orn(Tfa)^2′]GS from which another monoprotected derivative [Orn(Boc)²]GS was prepared in high yield. These unsymmetrically protected GS derivatives are versatile starting materials for the preparation of various other GS derivatives. As an example of application of the unsymmetrically protected derivatives, a dimeric GS derivative was prepared via a singly p-nitrobenzenesulfonyl(NBS)-activated derivative [Orn(Boc)²,Orn(NBS)^2′]GS.     

Solid-phase synthesis of human osteocalcin by using a γ-carboxyglutamic acid derivative

Human osteocalcin, also called bone Gla protein (BGP), consisting of 49 amino acids with two to three γ-carboxyglutamate residues, was chemically synthesized for the first time by a novel solid-phase peptide synthesis. An l -enantiomer of N-tert-butyloxycarbonyl-γ,γ′-dicyclohexyl-γ-carboxyglutaniic acid was designed, prepared and utilized as a monomeric compound and proven to be useful for the solid-phase peptide synthesis of human osteocalcin. The synthesis and optical resolution of the γ-carboxyglutamic acid (Gla) derivative are first described, followed by the synthesis and characterization of Gla¹⁷-human osteocalcin.     

1-(3-(9H-Carbazol-9-yl)-1-propyl)-4-(2-methoxyphenyl)-4-piperidinol,a novel subtype selective inhibitor of the mouse type II GABA-transporter

The selectivity of new derivatives of the γ-aminobutyric acid (GABA)-uptake inhibitor, tiagabine was characterized at the four cloned mouse GABA transporters (mGAT1 through mGAT4) by measuring [³H]-GABA uptake into stably transfected baby hamster kidney cells. While tiagabine is a highly selective inhibitor of mGAT1 (K_i=0.11±0.02 μM), these derivatives exhibited low potencies at mGAT1 but differential activities at mGAT2, mGAT3 and mGAT4. In particular, 1-(3-(9H-carbazol-9-yl)-1-propyl)-4-(2-methoxyphenyl)-4-piperidinol (NNC 05-2090) was a potent inhibitor of mGAT2 (K_i=1.4±0.3 μM) showing at least 10 fold selectivity over mGAT1, mGAT3 and mGAT4. NNC 05-2090 is the first subtype selective inhibitor of mGAT2 and may represent a novel useful tool for investigating the physiological roles of GAT2 in the brain and periphery.     

Conjugates of catecholamines. VII. Synthesis and β-adrenergic activity of peptide catecholamine conjugates†

A series of novel catecholamine derivatives has been prepared in which one of the N-methyl substituents of isoproterenol has been extended by a spacer consisting of a chain of four methylenes which terminates with an amide linkage to a peptide, the point of attachment being via the aromatic amino group of p-aminophenylalanine. In one of the derivatives, two catecholamines are attached to the same peptide in this manner. The peptides, which range in size from three to eight amino acid residues and contain phenylalanine, glycine, and L-α-amino-δ-hydroxyvaleric acid, were synthesized via stepwise and fragment condensation techniques. The β-adrenergic agonist activities of the derivatives were evaluated in vitro by measuring the intracellular accumulation of cyclic AMP in S49 mouse lymphoma cells.     

Convergent synthesis of two 14C‐labeled β3‐adrenergic receptor agonists

The synthesis of β₃‐adrenergic receptor agonists A and B with radiolabeled amide fragment, required for drug disposition studies, was accomplished based on initial formation of 2‐(4‐(2‐amino‐2‐methylpropyl)phenoxy)‐5‐[¹⁴C]‐cyanopyridine by the reaction of 2‐bromo‐5‐iodopyridine with para‐substituted phenol, and following cyanation of aromatic iodide with potassium cyanide‐[¹⁴C]. After the coupling of the resulted amine with glycidyl derivatives of 4‐hydroxyindole and 4‐hydroxycarbazole, the corresponding nitriles were hydrolyzed with basic hydrogen peroxide to obtain target amides A and B . Copyright © 2006 John Wiley & Sons, Ltd.     

From β‐N‐tert‐butyloxycarbonyl N‐carboxyanhydrides to β‐aminoacid derivatives

Abstract: β‐N‐tert‐butyloxycarbonyl‐N‐carboxyanhydrides are very reactive β‐amino acid derivatives. They react cleanly and smoothly with different nucleophiles like aminoesters, enolates, N‐methyl‐d ‐glucamine, amidoximes to afford in good to excellent yields peptides, β‐amino ketocompounds, β‐aminosugars and functionalized disubstituted 1,2,4‐oxadiazoles.