Synthesis of a new family of acyclic nucleoside phosphonates, analogues of TPases transition states

A 6-step procedure was developed for the synthesis of a new family of acyclic nucleoside phosphonates (ANPs), "PHEEPA" [(2-pyrimidinyl-2-(2-hydroxyethoxy)ethyl)phosphonic acids] in overall yields ranging from 4.5% to 32%. These compounds, which possess on one side a hydroxy function and on the other side a phosphonate group, can be considered either as potential antiviral agents or as transition state analogues of nucleoside phosphorylases such as thymidine phosphorylase.     

Enantiopurity analysis of new types of acyclic nucleoside phosphonates by capillary electrophoresis with cyclodextrins as chiral selectors

CE methods have been developed for the chiral analysis of new types of six acyclic nucleoside phosphonates, nucleotide analogs bearing [(3‐hydroxypropan‐2‐yl)‐1H‐1,2,3‐triazol‐4‐yl]phosphonic acid, 2‐[(diisopropoxyphosphonyl)methoxy]propanoic acid, or 2?(phosphonomethoxy)propanoic acid moieties attached to adenine, guanine, 2,6‐diaminopurine, uracil, and 5‐bromouracil nucleobases, using neutral and cationic cyclodextrins as chiral selectors. With the exception of the 5‐bromouracil‐derived acyclic nucleoside phosphonate with a 2‐(phosphonomethoxy)propanoic acid side chain, the R and S enantiomers of the other five acyclic nucleoside phosphonates were successfully separated with sufficient resolutions, 1.51–2.94, within a reasonable time, 13–28 min, by CE in alkaline BGEs (50 mM sodium tetraborate adjusted with NaOH to pH 9.60, 9.85, and 10.30, respectively) containing 20 mg/mL β‐cyclodextrin as the chiral selector. A baseline separation of the R and S enantiomers of the 5‐bromouracil‐derived acyclic nucleoside phosphonate with 2‐(phosphonomethoxy)propanoic acid side chain was achieved within a short time of 7 min by CE in an acidic BGE (20:40 mM Tris/phosphate, pH 2.20) using 60 mg/mL quaternary ammonium β‐cyclodextrin chiral selector. The developed methods were applied for the assessment of the enantiomeric purity of the above acyclic nucleoside phosphonates. The preparations of all these compounds were found to be synthesized in pure enantiomeric forms. Using UV absorption detection at 206 nm, their concentration detection limits were in the low micromolar range.     

Synthesis of acyclic nucleoside phosphonates as antiviral compounds

Reaction of 6‐chloropyrimidines with diethyl [(2‐aminoethoxy)methyl]phosphonate allows for a ready access to acyclic nucleoside phosphonates. A series of 5‐substituted pyrimidines bearing a phosphonate side chain at position 6 were synthesized and tested against herpes simplex viruses (HSV‐1 and HSV‐2) and human immunodeficiency virus (HIV‐1). Some compounds showed weak antiviral activity against HSV‐1.     

Copper‐Catalyzed α‐Amination of Phosphonates and Phosphine Oxides: A Direct Approach to α‐Amino Phosphonic Acids and Derivatives

A direct approach to important α‐amino phosphonic acids and its derivatives has been developed by using copper‐catalyzed electrophilic amination of α‐phosphonate zincates with O‐acyl hydroxylamines. This amination provides the first example of C? N bond formation which directly introduces acyclic and cyclic amines to the α‐position of phosphonates in one step. The reaction is readily promoted at room temperature with as little as 0.5 mol % of catalyst, and demonstrates high efficiency on a broad substrate scope.     

Determination of acid-base dissociation constants of azahelicenes by capillary zone electrophoresis

CZE was employed to determine acid-base dissociation constants (pK(a)) of ionogenic groups of azahelicenes in methanol (MeOH). Azahelicenes are unique 3-D aromatic systems, which consist of ortho-fused benzene/pyridine units and exhibit helical chirality. The pK(a) values of pyridinium groups of the studied azahelicenes were determined from the dependence of their effective electrophoretic mobility on pH by a nonlinear regression analysis. The effective mobilities of azahelicenes were determined by CZE at pH range between 2.1 and 10.5. Thermodynamic pK(a) values of monobasic 1-aza[6]helicene and 2-aza[6]helicene in MeOH were determined to be 4.94 +/- 0.05 and 5.68 +/- 0.05, respectively, and pK(a) values of dibasic 1,14-diaza[5]helicene were found to be equal to 7.56 +/- 0.38 and 8.85 +/- 0.26. From these values, the aqueous pK(a) of these compounds was estimated.     

Synthesis of 9-[(2-hydroxy-1-phosphonylethoxy)ethyl]guanine, 1-[(2-hydroxy-1-phosphonylethoxy)ethyl]cytosine and 9-[(2-hydroxy-1-phosphonylethoxy)ethyl] adenine

The acyclic nucleoside phosphonate analogues, 9-[(2-hydroxy-1-phosphonylethoxy)ethyl]guanine 6 , 1-[(2-hydroxy-1-phosphonylethoxy)ethyl]cytosine 7 and 9-[(2-hydroxy-1-phosphonylethoxy)ethyl]adenine 8 , have been prepared by the coupling of a tosylate of the phosphonate side chain 12 with a purine or pyrimidine base followed by deprotection of the blocking groups.     

Copper‐Catalyzed Asymmetric Synthesis of Tertiary α‐Hydroxy Phosphonic Acid Derivatives with In Situ Generated Nitrosocarbonyl Compounds as the Oxygen Source

α‐Hydroxy phosphonic acids and their derivatives are highly bioactive structural motifs. It is now reported that these compounds can be accessed through the copper‐catalyzed direct α‐oxidation of β‐ketophosphonates using in situ generated nitrosocarbonyl compounds as an electrophilic oxygen source. These reactions proceeded in high yields (up to 95 %) and enantioselectivities (up to >99 % ee) for both cyclic as well as acyclic substrates. This method was also applied for the synthesis of α,β‐dihydroxy phosphonates and β‐amino‐α‐hydroxy phosphonates.     

Migration mechanism of bases and nucleosides in oil-in-water microemulsion capillary electrophoresis.

The electrophoretic behaviors of five bases and corresponding nucleosides in the oil in water (o/w) microemulsion capillary electrophoresis, microemulsion electrokinetic chromatography (MEEKC), were examined in comparison with those in normal capillary zone electrophoresis (CZE). The microemulsion systems were composed of heptane, sodium dodecyl sulfate (SDS), 1-butanol and 10 mM phosphate buffer (pH 7.0) or toluene, SDS, 1-butanol and 5 mM carbonate buffer (pH 10.0). CZE was carried out in the range of pH 9.7-10.9, and the dissociation constants, pKa, of the bases and nucleosides and the electrophoretic mobilities of the anionic forms were determined. The electrophoretic behaviors of the solutes in the microemulsion systems were analyzed from their pKa, the electrophoretic mobilities of the anions determined by CZE, and the distribution constants, K(D), of the neutral forms between the microemulsion droplets and the outer aqueous phase. The importance of adsorption mechanism in MEEKC system was suggested from the correlation between log K(D) and log P.     

Synthesis and molecular structure of new acyclic analogues of nucleotides with a 1,2-alkadienic skeleton

Reaction of 1-chloro-4-(diethoxyphosphonyl)alka-2,3-dienes 14,15 with purine and pyrimidine heterocyclic bases in the presence of cesium carbonate afforded new acyclic analogues of nucleotides containing a 1,2-alkadienic skeleton 18-23. Dealkylation of 18-23 furnished phosphonic acids 2a-f. In contrast, alkylation reaction with 1-chloro-4-(diethoxyphosphonyl)octa-2,3-diene 16 led to Z- and E-1,3-alkadienic phosphonates 25a,b and 26a,b. A similar reaction with 1-chloro-4-(diethoxyphosphonyl)-2-methylbuta-2,3-diene 17 led to the elimination of hydrochloride and formation of 4-(diethylphosphonyl)-2-methylbut-1-en-3-yne 24. Molecular structures of new acyclic nucleotides 18 and 2f are determined by X-ray crystallographic analysis.     

Synthesis of phosphonomethoxyethyl or 1,3-bis(phosphonomethoxy)propan-2-yl lipophilic esters of acyclic nucleoside phosphonates

A new alternative synthetic pathway towards mono and diesters of acyclic nucleoside phosphonates (PMEA, PMEC and PMEG) or [1,3-bis(phosphonomethoxy)propan-2-yl]adenine bearing one or two hexadecyloxypropyl ester groups (CH₂)₃O-n-C₁₆H₃₃ is reported.     

New mixed phosphonate esters by transesterification of pinacol phosphonates and their use in aldehyde and ketone coupling reactions with nonstabilized phosphonates

Alkylpinacol phosphonates were prepared by rhodium-catalyzed olefin hydrophosphorylation, and attempted alpha-deprotonation of the pinacol derived alkyl phosphonates resulted in ring cleavage. The propensity of the alkylpinacol phosphonates to undergo ring opening was exploited to prepare phosphonic acid monomethyl esters in high yield by transesterification in acidulated methanol. Esterification and alkylation with aldehydes or ketones gave beta-hydroxy mixed phosphonate esters. tert-Butyl and benzylic phosphonate ester protective groups were introduced to improve the efficiency and functional group compatibility of beta-hydroxy phosphonate saponification. The beta-hydroxy phosphonic acid monomethyl esters were dehydrated with diisopropylcarbodiimide, which gave oxaphosphetane intermediates that collapse to an olefin. The overall reaction sequence complements the arsenal of Horner-Wadsworth-Emmons-type coupling reactions.     

毛细管区带电泳法测定3种香豆素的离解常数

采用毛细管区带电泳法(CZE)测定瑞香苷(DN)、瑞香素(DP)和7-羟基香豆素(7-HC)的离解常数(p Ka).通过测试不同酸度条件下各香豆素的迁移时间,以香豆素在电泳中有效淌度和运行液中OH-浓度的关系,推导了毛细管区带电泳-紫外分光光度(CZE-UV)法测定3种香豆素离解常数(p Ka)的线性模型,并建立了这3种香豆素的p Ka测定方法.测得3种香豆素的p Ka值分别是7.43(7-HC)、6.91(DN)和6.86(DP).同时也采用传统方法 -紫外分光光度法对这些物质的p Ka进行测定以验证CZE的可靠性,两种测定结果相一致,说明CZE-UV法用于3种香豆素的离解常数的测定,快速、简便、结果可靠.     

Determination of pKa values by capillary zone electrophoresis with a dynamic coating procedure

CZE allows to measure the acidic dissociation constant (pKa) of many drug substances. However, determining the EOF intensity may be time-consuming, especially at a low pH. In order to overcome this drawback, a dynamic coating procedure of the capillary was carried out to increase microEOF, and thus to reduce the analysis time. In addition, this coating procedure enhanced migration time stability. The effective mobilities of 15 compounds were measured at different pH, producing pK'a values dependent on BGE ionic strength. The latter values were corrected with the activity coefficient to obtain a "true" pKa value. The 15 investigated compounds were (i) five acids: namely, salicylic acid, benzoic acid, ketoprofen, phenobarbital, and phenol, (ii) four bases: lidocaine, propafenone, propranolol, and quinine, (iii), five ampholytes: sulfanilamide, sulfabenzamide, sulfadimethoxine, sulfadoxine, and sulfisoxazole, and (iv) one zwitterion: cetirizine. The range of determined pKa values was between 1.2 and 11.2, and close to the pKa values available from the literature.     

Determination of dissociation constants of amino acids by capillary zone electrophoresis.

A method is proposed for the determination of dissociation constants of amino acids by capillary zone electrophoresis. According to the dissociation equilibrium of amino acids and the basic theory of electrophoresis, the nonlinear relationship between the pH value of the buffer and the effective electrophoretic mobilities of the analyte was obtained. The dissociation constants can be calculated from the pH values and the corresponding effective electrophoretic mobilities using the program written in C++. The dissociation constants, pKa1 and pKa2, of 11 kinds of amino acids were determined successfully by the proposed method. The determined dissociation constants were compared with values in the literature; the differences between them are in the range of -0.03 to 0.06. No significant differences were observed between the determined dissociation constants and the corresponding literature values.     

Background electrolytes in 50% methanol/water for the determination of acidity constants of basic drugs by capillary zone electrophoresis

The acidic dissociation constants of several hydrophobic drugs, amiodarone and a series of antidepressants that show a secondary or tertiary amino group, were determined in a 50% methanol/water mixture by capillary zone electrophoresis. The electrophoretic behavior of buffers prepared from sodium acetate, tris(hydroxymethyl) aminomethane hydrochloride, sodium hydrogenphosphate, ammonium chloride, ethanolamine, butilammonium chloride, and sodium borate in the hydroalcoholic solution was tested. Thus, all of them follow the Ohm's law until about 25 kV and, therefore, they can be used without significant Joule heat dissipation at 20 kV. For the studied drugs, buffers prepared with phosphate or borate give effective mobility measurements lower than those from other buffers. The wide pKa range of the studied drugs provides a wide pH range where the protonated forms of the amino compounds coexist with hydrogenphosphate ions and where the neutral amines coexist with boric acid. The decrease of the experimental effective mobilities in these instances can be explained through the interactions between coexisting species. Therefore, phosphate and borate buffers should be avoided to determine the mobility of amines with aqueous pKa higher than 8, at least in solutions with high methanol content. Independent measurements of acidic dissociation constants of drugs validate this statement.     

Preparation,crystal and molecular structure,and evaluation of plant growth regulating activity of guanidinoalkanephosphinates and phosphonates

A series of previously unknown α-guanidinoalkanephosphonous, α- and β-guanidinoalkanephosphonic acids has been prepared in order to study their structures and biological activity. Aminoalkanephosphonous and phosphonic acids have been converted into their guanidino derivatives by means of S-methylisothiourea hydroiodide or cyanamide amidination. The crystal and molecular structures of three guanidino acids have been determined by single-crystal X-ray diffraction. The plant growth regulating activity of all synthesized guanidinoalkanephosphinates and phosphonates has been evaluated on Lepidium sativum. © 1995 John Wiley & Sons, Inc.     

Capillary zone electrophoresis of cationic and anionic drugs in methanol

The actual mobilities and dissociation constants of acidic and basic pharmaceuticals were determined in methanol. Actual mobilities were derived from the dependence of the effective mobilities of the analytes on the pH of the methanolic background electrolyte solution (pH(MeOH)). The pKa values of the pharmaceuticals in methanol (pK(a,MeOH)) were calculated by non-linear curve fitting to the measured mobility values. It was found that the shift in pKa value (when compounds were transferred from water to methanol) increased with the acidity of the analyte. The average pKa shift for compounds exhibiting acidic properties in water was ca. 5.5 units, and the shift for basic compounds about 2 units. As was shown for a mixture of beta-blockers, the calculated actual mobilities and pKa values can be utilised in the optimisation of pH conditions for separation. The practical value of the method was illustrated by the analysis of urine samples.     

Radical Addition of Bis(Trimethylsilyl)Phosphonate to Vinyltrimethylsilane: Crystal Structure of (2-Trimethylsilylethyl)Phosphonic Acid

Abstract

The formation of phosphorus-carbon bond by free radical addition of phosphorus compounds containing P-H bond to olefins has been known since more than three decades ago. Alkyl or aryl phosphins, phosphinates, phosphonates and phosphorus or hypophosphorus acid have been used in these reactions, but a little attention have been paid to silyl phosphonates. As a part of ongoing study on the structure and reactivity of organosilicon-phosphonate compounds, we synthesized bis(trimethylsi1yl) (2-trimethylsilylethyl)phosphonate (I) by the reaction of bis(trimethylsily1) phosphonate with vinyltrimethylsilane in the presence of a peroxide. The product was characterized by its ¹H and ³¹P NMR and IR spectra. Hydrolysis of (I) led to the formation of corresponding phosphonic acid (n). The crystal structure of (11) has been determined by X-ray diffraction analysis.     

Synthesis of 5'-amino-5'-phosphonate analogues of pyrimidine nucleoside monophosphates

The 5'-amino-5'-phosphono derivatives of cytidine, cytosine arabinoside (ara-C), and uridine have been prepared via the corresponding nucleoside aldehydes. Phosphite addition to imines derived from the nucleoside aldehydes and p-methoxybenzylamine was efficient, and use of this amine allowed cleavage of the products to the parent amino phosphonic acids. The phosphite additions proved to be diastereoselective, with the cytidine and uridine derivatives favoring the 5'S stereochemistry and the ara-C derivative favoring the 5'R isomer. The stereochemistry of one cytidine derivative was established by single-crystal diffraction analysis, and detailed comparisons of the (13)C NMR data allowed assignments of the other amino phosphonates.     

Acyclic immucillin phosphonates: second-generation inhibitors of Plasmodium falciparum hypoxanthine-guanine-xanthine phosphoribosyltransferase

Plasmodium falciparum, the primary cause of deaths from malaria, is a purine auxotroph and relies on hypoxanthine salvage from the host purine pool. Purine starvation as an antimalarial target has been validated by inhibition of purine nucleoside phosphorylase. Hypoxanthine depletion kills Plasmodium falciparum in cell culture and in Aotus monkey infections. Hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRT) from P. falciparum is required for hypoxanthine salvage by forming inosine 5'-monophosphate, a branchpoint for all purine nucleotide synthesis in the parasite. Here, we present a class of HGXPRT inhibitors, the acyclic immucillin phosphonates (AIPs), and cell permeable AIP prodrugs. The AIPs are simple, potent, selective, and biologically stable inhibitors. The AIP prodrugs block proliferation of cultured parasites by inhibiting the incorporation of hypoxanthine into the parasite nucleotide pool and validates HGXPRT as a target in malaria.