An effective organic solvent system for the dissolution of amino acids

Dimethylformamide containing strong acids (CF₃ COOH, HBF₄. TosOH, etc.) and an excess of tertiary base with p^K≤6 is an effective solvent system for the dissolution of amino acids and their derivatives. The preferable base is pyridine, which forms a system with an apparent pH of 5.3. Amino acids dissolved in this solvent system readily interact with acylating reagents (BOC₂O, ZOSu, Fmoc-OSu and activated derivatives of N-protected amino acids). A number of BOC-, Z-, Fmoc-amino acids, as well as several dipeptides, were synthesized using this solvent system with 80-99%) yields. © Munksgaard 1996.     

Comparisons of pKa and log P values of some carboxylic and phosphonic acids: Synthesis and measurement

The changes in the physiochemical properties accompanying the substitution of a phosphonic acid group for a carboxylic acid group on various heterocyclic platforms was determined. A series of low molecular weight heterocyclic carboxylic and phosphonic acids was prepared, and the acid dissociation content (pKa) and log P values were measured potentiometrically. These values were compared to those of substituted benzene phosphonic acids, carboxylic acids, sulfonamides, and tetrazoles. The carboxylic acids included 3 pyrazoles, an imidazole, a triazole, 2 pyrimidine, and 6 aryl compounds. The phosphonic acids included a triazole, 2 pyrazoles, 4 pyrimidines, a thiophene, and 6 aryl compounds. Most of the compounds synthesized had adequate water solubility, although a simple methyl substituent in 2 series had a great effect, completely changing the properties. Log P values for the synthesized carboxylic and phosphonic acid compounds were below 2, and pK₁ values for the heterocyclic phosphonic acids were generally 2 to 3 log units lower than for the heterocyclic carboxylic acids.     

Synthesis of substituted pyridinecarboxylic acids and study of their properties

A series of substituted pyridinecarboxylic acids and their N-oxides has been synthesized, their dissociation constants and electrophoretic mobility have been measured, and their pharmacological action has been studied. The presence of a satisfactory correlation between the pKa of of 4-substituted pyridinecarboxylic acids or their oxides and the _p electronegativity constants of the substituents has been shown. A linear dependence between dissociation constants and electrophoretic mobility of pyridinecarboxylic acids or their N-oxides has been found in various buffer solutions. The pharmacological action of a number of the synthesized compounds has been studied.Translated from Khimiko-Farmatsevticheskii Zhurnal, No.5, pp. 3–10, May, 1967.     

N-ω-Carbethoxypentyl-4-quinolones: A New Class of Leukotriene Biosynthesis Inhibitors

6-[(4-Quinolinyl)oxy]hexanoic acids and the corresponding esters were designed and synthesized as inhibitors of the production of arachidonic acid metabolites. The inhibitory activities were assayed in vitro by evaluation of serum leukotriene B₄ and thromboxane B₂ production. While all 6-[(4-quinolinyl)oxy]hexanoic acids and their esters proved to be inactive, the N-alkyl-4-quinolones, obtained as by-products in their synthesis, were found to be a new class of leukotriene biosynthesis inhibitors.     

Potentielle Reaktivatoren der Acetylcholinesterase 2. Mitt.: Bisquartäre N-Alkoxypyridinium-carbaldoxime

Potential Reactivators of Acetylcholine Esterase. Part 2 Salts of bis(hydroximinomethylpyridiniooxy)-alkanes (BA) are synthesized by alkylation of pyridine-N-oxide-carbaldoximes with bisesters of electronegatively substituted arylsulfonic acids in the presence of DMSO. pK_a's, UV-, IR-, and NMR-spectra are discussed, especially with respect to configuration assignments of the oxime functions.     

Solid-phase synthesis of H- and methylphosphonopeptides

We introduce solid-phase syntheses of H- and methylphosphonopeptides, giving access for the first time to a new class of mimics for o-phosphoamino acids. The model peptides H-GlyGlyXaaAla-OH (Xaa = Ser, Thr) were synthesized on a solid-phase using Fmoc/^tBu strategy and HBTU/HOBt activation by incorporation of hydroxyl-protected serine and threonine. As selectively cleavable hydroxyl-protecting groups we used triphenylmethyl and tert-butyldimethylsilyl for both amino acids, as described in the literature. All peptides were phosphitilated with O,O-di-tert-butyl-N,N-diethylphosphoramidite and yielded H-phosphonopeptides after trifluoroacetic acid cleavage. Alternatively we phosphonylated the peptides with O-tert-butyl-N,N-diethyl-P-methylphosphonamidite, which was synthesized by a two-step one-pot procedure starting from commercially available chemicals. All H- and methylphosphonopeptides were obtained in high purities and yields, as shown by reversed-phase high-performance liquid chromatography and anion-exchange chromatography. The phosphonopeptides were characterized by ¹H and ³¹P NMR. We confirmed their molecular masses by electrospray mass spectrometry and analyzed their fragmentation schemes, which seemed to be characteristic for each class of analogues. The H-phosphonopeptides lost phosphonic acid (H₃PO₃, 82 mass units) and the methylphosphonopeptides lost methylphosphonic acid (MeH₂PO₃, 96 mass units). Both H- and methylphosphonopeptides represent a new and simply accessible class of mimics for phosphopeptides. Compared with the corresponding phosphopeptides all phosphonopeptides were synthesized in higher yields and purities (>80%). © Munksgaard 1996.     

Synthesis and biological activity of cyclohexylamine derivatives

2-(p-hydroxyphenyl)cyclohexylamides were synthesized from ω-chlorocarboxylic acids using the Ritter reaction. Subsequent reduction under the action of LiAlH₄ led to the corresponding substituted cyclic amines. The acute toxicity, analgesic properties, and antidepressant activity of the synthesized compounds were studied and their action on locomotion and exploration activity in the open-field test was evaluated. __________ Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 40, No. 6, pp. 8–12, June, 2006.     

阿魏酸衍生物的合成

本文报道3种类型18个阿魏酸衍生物的化学合成:Ⅰ.氨基醇酯类化合物,Ⅱ.5-(烷胺基)一次甲基阿魏酸,Ⅲ.双分子阿魏酸的醚类化合物。药理筛选的初步结果表明:Ⅰ类化合物的体外抗凝作用比阿魏酸本身为强,Ⅱ类化合物作用很弱。     

Synthesis and properties of equine β-melanotropin analogs with substitution in residue position 1

Five analogs of equine β-melanotropin have been synthesized by the solid phase method. The NH₂-terminal aspartic acid was substituted with amino acids (Gly, Trp, Ile, Lys and Nα-acetyl-Asp) differing widely in physicochemical properties. On the basis of their lipolytic potencies it was concluded that this position plays a negligible role in this activity.     

Amino monothio acids in solid-phase synthesis of peptide thioamides

Peptides containing backbone thioamides (endothiopeptides) have been synthesized utilizing thioacylation under solid-phase conditions. The thioacylations were performed by activating N-protected amino monothio acids with the phosphorus-containing coupling reagent 6-nitrobenzotriazol-1-yloxytris(pyrrolidino)phosphonium hexafluorophosphate (PyNOP). This method avoids the use of P₄S₁₀-based O/S-exchange reagents, and it is thus amendable to amino acids with side-chain amides. Synthesis of endothio analogs of biologically active peptide such as pGlu-ψ[CSNH]-His-Pro-NH₂ (TRH) and Leu-Gln-ψ[CSNH]-Leu-Lys demonstrated this feature. Proton and carbon NMR spectra of the TRH analog verified the sequential position of its thioamide function. Compatibility of endothiopeptides with allyl-protecting groups was studied, and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) was evaluated as a substitute for piperidine. © Munksgaard 1996.     

Synthesis and antimicrobial activity of cyclopentyl-substituted halogenophenoxyacetic acids and their amides

A series of cyclopentylhalogenoanisoles have been synthesized by alkylation of o- and p-chloro- and fluoroanisoles with cyclopentene in the presence of BF₃·H₃PO₄. The compositions and structures of the products were studied by GC, IR, and NMR spectroscopy. Demethylation of the cyclopentylhalogenoanisoles yielded cyclopentylhalogenophenols, which were reacted with chloroacetic acid and chloroacetamide to obtain cyclopentyl-substituted chloro- and fluorophenoxyacetic acids and their amides. Results of studying the antimicrobial activity of the synthesized acids and their amides against S. viridans, S. flexneri, P.aeruginosa, B. antracoides, K. rhinoscleromatis, and C. albicans are presented. All substances show moderate activity against the test microbes (minimum bacteriostatic concentrations from 31.25 to 125 μg/mL). Introduction of a cyclopentyl substituent into the structure of 2-chlorophenoxyacetic acid improves the activity against S. viridans, P. aeruginosa, and K. rhinoscleromatis. These data can be used to study the relationship between the structures and antimicrobial activity.     

Synthesis and biological activity of some new 3,6-dinitro-1:8-naphthaloyl-and 3,6-diamino-1:8-naphthaloylamino acids and dipeptide derivatives

Synthesis of a series of 3,6-dinitro-1:8-naphthaloylamino acids (II-IX) and some of their corresponding methyl esters (X-XVI) and 3,6-diamino-1:8-naphthaloylamino acid derivatives (XXIX-XXXVI) is described. Coupling of 3,6-dinitro-1:8-naphthaloylamino acids with amino acid methyl ester hydrochlorides in dioxane-DMF-Et₃N medium using DCC method furnishes the desired 3,6-dinitro-1:8-naphthaloyldipeptide methyl esters (XVII-XXVIII). Most of the synthesized 3,6-dinitro-1:8-naphthaloylamino acids, esters and dipeptide derivatives (compounds III-VI, XI-XV, XVII, XIX-XXI, XXIII and XXV) and 3,6-diamino-1:8-naphthaloylamino acid derivatives (XXIX-XXXV) were found to be active against a number of microorganisms.     

Design, synthesis and cytotoxicity of a new series of isoxazolidine based nucleoside analogues

5‐Arylisoxazolidin‐3‐yl‐3‐diethoxyphosphonates have been synthesized from N‐methyl‐C‐diethoxyphosphorylnitrone and vinyl aryls in good yields and their transformation into the respective phosphonic acids has been accomplished via dealkylation procedure using trimethylsilyl bromide. Phosphonates having 1‐ and 2‐naphthyl substituents at C5 in the isoxazolidine ring as well as the respective phosphonic acids have been found cytotoxic to HeLa and K562 cells with IC₅₀ in the 0.1–0.3 mM range. Preliminary studies on mechanism of action imply that intercalation to DNA is not responsible for their cytotoxic properties.     

甾体不对称合成的研究Ⅶ.新法合成2-烷基-2-(3′-羰基-6′-甲氧基羰基)-己基-1,3-环戊二酮

本文报道以丙烯醛为原料经γ-羰基亚砜合成了2-烷基-2-(3′-羰基-6′-甲氧基羰基)-己基-1,3-环戊二酮(2 a,b),7步总产率分别为13%和17%。2 a,b经微生物或S-氨基酸的不对称合成即得光学活性甾体药物全合成的合成原。     

Conformational preferences of oligopeptides rich in α-aminoisobutyric acid. III. Design,synthesis and hydrogen bonding in 310-helices

Two sterically constrained peptides {ⁱBoc-Aib-Aib-Aib-DkNap-Leu-Qx-Ala-Aib-Aib-F1, (Dk⁴Qx⁶[7/9]) and ⁱBoc-Aib-Aib-Aib-DkNap-Leu-Aib-Ala-Aib-Aib-Fl, (Dk⁴7/9)} containing α-aminoisobutyric acid (Aib) and Aib-class amino acids in conjunction with selected mono-α-alkyl amino acids were synthesized by an optimized TBTU/HOBt procedure. The use of Aib-class amino acids (e.g. DkNap and Qx), defined and discussed here, gives rise to the same overwhelmingly 3₁₀-helical backbone conformation as that provided by simpler Aib-rich peptides and homopeptides. The synthetic α,α-dialkylamino acids (DkNap, Qx) are aromatic homologues of the known alicyclic variants of Aib, the Ac₅c and Ac₆c amino acids. Two new organic solubilizing groups for peptides, ⁱBoc and 2-methoxyethylamine, are introduced. The ¹H nuclear magnetic resonance analyses of the Dk⁴s/p[7/9] and Dk⁴Qx⁶[7/9] peptides demonstrate the unambiguous 310s/b-helical hydrogen bonding pattern of these peptides, confirming the design objective of these sequence patterns containing greater than 50% Aib and Aib-class composition. © Munksgaard 1994.     

Synthesis of side-chain to side-chain cyclized peptide analogs on solid supports

Cyclic peptide structures of the type -Lys-R₁—R_n-Glu- can be synthesized on the Merrifield resin by assembling the peptide chain using Nα-Fmoc-amino acids and Boc and tert.-butyl protection for the side-chains of Lys and Glu, respectively. If residues R₁ to R_n contain side-chain functional groups, TFA-resistant protection is required. After TFA treatment cyclization on the resin can be performed with appropriate coupling reagents. The formation of such cyclic structures may be preceded or followed by peptide chain assembly using Nα-Boc-amino acids and the entire peptide chain containing the cyclic portion is finally cleaved by HF treatment. Using this principle we synthesized the following opioid peptide related cyclic analogs: H-Tyr-d -Lys-Gly-Phe-Glu-NH₂ (I), H-Tyr-Lys-Gly-Phe-Glu-NH₂ (II), H-Tyr-d -Lys-Phe-Glu-NH₂ (III), H-Tyr-d -Glu-Gly-Phe-Lys-NH₂ (IV), H-Tyr-d -Glu-Phe-Lys-NH₂ (V), H-Tyr-d -Orn-Gly-Glu-NH₂ (VI) and H-Tyr-d -Ala-Lys-Phe-Glu-NH₂ (VII). Cyclic monomers were obtained in all cases, as demonstrated by mass spectrometry. Analysis of side-products revealed a slow-down of the HF deprotection of O-benzylated tyrosine as a consequence of hydrophobic interactions as well as the formation of a side-chain-linked antiparallel cyclic dimer in the case of compound VI. In conclusion, the described method permits the convenient preparation of peptide analogs cyclized via amide bond formation between side-chain amino and carboxyl groups in reasonable yield.     

A propeller‐like small molecule as a novel G‐quadruplex DNA binder: The study of fluorescent sensing property and preferential interactions with human telo21 structure

A new propeller‐like small molecule was synthesized with three terminal amino side groups. The molecule was found to be a selective nucleic acid binder towards telo21 G‐quadruplex DNA compared with other representative nucleic acids including single‐stranded DNA (dA21), duplex DNA (ds26) and RNA. The fluorescent signal of the molecule upon interaction with telo21 G‐quadruplex structure shows remarkable enhancement (F_max/F₀ = 17.9) while interaction with other nucleic acids shows the signal enhancement which is less than 2.1. In addition, a good linear relationship of binding signal correlated with the concentration of telo21 DNA was obtained. Molecular docking study was also performed to acquire the binding behaviour and its interaction modes of the molecule with the structure of human telomeric DNA G‐quadruplex. The modelling results show that the three conjugated terminal units (dimethylaminobenzyl groups) associated through the ethylene bridges with the central methylated pyridine ring formed a co‐planar conformation upon stacking onto the G‐quartets via pi‐pi stacking interactions. This could be the key reason that the molecule shows excellent fluorescent signal of binding towards telo21 G‐quadruplex DNA rather than other types of nucleic acids.     

p-Chlorotetrafluorophenyl esters of N-protected amino acids

p-Chlorotetrafluorophenyl (Tfc) esters of protected amino acids and peptides are more reactive than are the well known pentafluorophenyl (Pfp) esters. Two reagents, p-chlorotetrafluorophenyltrifluoroacetate (Tfc-OTfa) and di-(p-chlorotetrafluorophenyl)carbonate (di-Tfc-carbonate), can be used for their syntheses, thereby avoiding use of the allergic dicyclohexylcarbodiimide. This is especially important for bulk preparations. Many Fmoc- and Boc-amino acid-OTfc esters have been synthesized and characterized. The hexadecameric tanden1 repeat H-(AlaAlaLysPro)₄-OH was synthesized using di-Tfc-carbonate for the preparation of Tfc-esters.     

Synthesis of N-carboxyalkyl and N-aminoalkyl functionalized dipeptide building units for the assembly of backbone cyclic peptides

Abstract: To improve the assembly of backbone cyclic peptides, N-functionalized dipeptide building units were synthesized. The corresponding N-aminoalkyl or N-carboxyalkyl amino acids were formed by alkylation or reductive alkylation of amino acid benzyl or tert-butyl esters. In the case of N-aminoalkyl amino acid derivatives the aldehydes for reductive alkylation were obtained from N,O-dimethyl hydroxamates of N-protected amino acids by reduction with LiAlH₄. N-carboxymethyl amino acids were synthesized by alkylation using bromoacetic acid ester and the N-carboxyethyl amino acids via reductive alkylation using aldehydes derived from formyl Meldrums acid. Removal of the carboxy protecting group leads to free N-alkyl amino acids of very low solubility in organic solvents, allowing efficient purification by extraction of the crude product. These N-alkyl amino acids were converted to their tetramethylsilane-esters by silylation with N,O-bis-(trimethylsilyl)acetamide and could thus be used for the coupling with Fmoc-protected amino acid chlorides or fluorides. To avoid racemization the tert-butyl esters of N-alkyl amino acids were coupled with the Fmoc-amino acid halides in the presence of the weak base collidine. Both theN-aminoalkyl and N-carboxyalkyl functionalized dipeptide building units could be obtained in good yield and purity. For peptide assembly on the solid support, the allyl type protection of the branching moiety turned out to be most suitable. The Fmoc-protected N-functionalized dipeptide units can be used like any amino acid derivative under the standard conditions for Fmoc-solid phase synthesis.     

Fmoc/Trt-amino acids: comparison to Fmoc/tBu-amino acids in peptide synthesis

Model peptides containing the nucleophilic amino acids Trp and Met have been synthesized with the application of Fmoc/Trt- and Fmoc/tBu-amino acids, for comparison. The deprotection of the peptides synthesized using Fmoc/Trt-amino acids in all cases leads to crude peptides of higher purity than that of the same peptides synthesized using Fmoc/tBu-amino acids. © Munksgaard 1998.