Divergent strategy for the synthesis of alpha-aryl-substituted fosmidomycin analogues

Fosmidomycin is the first representative of a new class of antimalarial drugs acting through inhibition of 1-deoxy-D-xylulose 5-phosphate (DOXP) reductoisomerase (DXR), an essential enzyme in the non-mevalonate pathway for the synthesis of isoprenoids. This work describes a divergent strategy for the synthesis of a series of alpha-aryl-substituted fosmidomycin analogues, featuring a palladium-catalyzed Stille coupling as the key step. An alpha-(4-cyanophenyl)fosmidomycin analogue emerged as the most potent analogue in the present series. Its antimalarial activity clearly surpasses that of the reference compound fosmidomycin.     

Assay of 1-hydroxy-3-aminopropylidene-1,1-bisphosphonate and related bisphosphonates in human urine and plasma by high-performance ion chromatography

A method is described for the analysis of 1-hydroxy-3-aminopropylidene-1, 1-bisphosphonate and related bisphosphonates in human urine and plasma. Samples are spiked with 1-hydroxy-5-aminopentylidene-1,1-bisphosphonate as an internal standard and calcium chloride is added to precipitate the bisphosphonates. Following centrifugation the precipitate is redissolved in acetic acid, and the bisphosphonates are separated by high-performance ion chromatography on a Dionex AS7 column using nitric acid as mobile phase. The bisphosphonates are oxidised to orthophosphate using post-column addition of ammonium persulphate and this is followed by post-column reaction with molybdenum-ascorbate to yield the phosphomolybdate chromophore which is detected at 820 nm. A detection limit of 10 ng/ml is possible.     

Isoprenoid biosynthesis via the MEP pathway. Synthesis of (3,4)-3,4-dihydroxy-5-oxohexylphosphonic acid, an isosteric analogue of 1-deoxy-D-xylulose 5-phosphate, the substrate of the 1-deoxy-D-xylulose 5-phosphate reducto-isomerase

(3,4)-3,4-Dihydroxy-5-oxohexylphosphonic acid, an isosteric analogue of 1-deoxy-D-xylulose 5-phosphate (DXP), was obtained in enantiomerically pure form from (+)-2,3--benzylidene--threitol by a seven-step sequence. This phosphonate did not affect the growth of. It did not inhibit the 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), but was converted by this enzyme into (3,4)-3,4,5-trihydroxy-3-methylpentylphosphonic acid, an isosteric analogue of 2-C-methyl-D-erythritol 4-phosphate. The enzyme was, however, less efficient with the methylene phosphonate analogue than with the natural substrate.     

Enthalpy versus entropy-driven binding of bisphosphonates to farnesyl diphosphate synthase

We report the results of an ITC (isothermal titration calorimetry) investigation of the binding of six bisphosphonates to the enzyme farnesyl diphosphate synthase (FPPS; EC 2.5.1.10) from Trypanosoma brucei. The bisphosphonates investigated were zoledronate, risedronate, ibandronate, pamidronate, 2-phenyl-1-hydroxyethane-1,1-bisphosphonate, and 1-(2,2-bisphosphonoethyl)-3-iodo pyridinium. At pH = 7.4, both risedronate and the phenylethane bisphosphonate bind in an enthalpy-driven manner (DeltaH approximately -9 to 10 kcal mol-1), but the other four bisphosphonates bind in an entropy-driven manner (DeltaS varying from 31.2 to 55.1 cal K-1 mol-1). However, at pH = 8.5, zoledronate binding switches from entropy to enthalpy-driven. The DeltaG results are highly correlated with FPPS inhibition results obtained using a radiochemical assay (R2 = 0.85, N = 11, P < 0.001). The DeltaH and DeltaS results are interpreted in terms of a model in which bisphosphonates with charged side chains have positive DeltaH values, due to the enthalpic cost of desolvation (due to strong ion-dipole interactions) and, likewise, a positive DeltaS, due to an increase in water entropy (both ligand and protein associated) on ligand binding to FPPS: the hydrophobic effect. For the neutral side chains (risedronate at pH 7.4, 8.5 and zoledronate at pH 8.5, as well as the phenylethane bisphosphonate), binding is overwhelmingly enthalpy-driven, with the enhanced activity of the basic side chain containing species being attributable to their becoming protonated in the active site. Given the large size of the bisphosphonate market and the potential importance of the development of these compounds for cancer immunotherapy and anti-parasitic chemotherapy, these results are of broad general interest in the context of the development of new, potent, and selective FPPS inhibitors.     

α,α-Difluorophosphonohydroxamic Acid Derivatives among the Best Antibacterial Fosmidomycin Analogues

Three α,α-difluorophosphonate derivatives of fosmidomycin were synthesized from diethyl 1,1-difluorobut-3-enylphosphonate and were evaluated on Escherichia coli. Two of them are among the best 1-deoxy-d-xylulose 5-phosphate reductoisomerase inhibitors, with IC₅₀ in the nM range, much better than fosmidomycin, the reference compound. They also showed an enhanced antimicrobial activity against E. coli on Petri dishes in comparison with the corresponding phosphates and the non-fluorinated phosphonate.     

Symmetrical and Asymmetrical Bisphosphonate Esters. Synthesis, Selective Hydrolysis, and Isomerization

Summary. Two simple and efficient one-pot procedures for the synthesis of a series of α-branched N-heterocycle-substituted methane-1,1-bisphosphonates are outlined. In the first method, the parent halosubstrates were reacted with cyanomethylphosphonate followed by reaction with dialkyl phosphonates to give asymmetrical or symmetrical bisphosphonates (BPs). In the second approach, the same halocompounds were reacted with tetraethyl methyl-1,1-bisphosphonate to give the requisite BPs. Partial and complete hydrolysis of the prepared BPs were also investigated. The products contain functional groups advantageous for further synthetic modification as structural units for coupling with the drug.     

Symmetrical and Asymmetrical Bisphosphonate Esters. Synthesis, Selective Hydrolysis, and Isomerization

Two simple and efficient one-pot procedures for the synthesis of a series of α-branched N-heterocycle-substituted methane-1,1-bisphosphonates are outlined. In the first method, the parent halosubstrates were reacted with cyanomethylphosphonate followed by reaction with dialkyl phosphonates to give asymmetrical or symmetrical bisphosphonates (BPs). In the second approach, the same halocompounds were reacted with tetraethyl methyl-1,1-bisphosphonate to give the requisite BPs. Partial and complete hydrolysis of the prepared BPs were also investigated. The products contain functional groups advantageous for further synthetic modification as structural units for coupling with the drug.     

Improved determination of the bisphosphonate pamidronate disodium in plasma and urine by pre-column derivatization with fluorescamine, high-performance liquid chromatography and fluorescence detection.

An improved method for the determination of 1-hydroxy-3-aminopropylidene-1,1-bisphosphonate (pamidronate) in human urine and plasma is described. The procedure is based on a co-precipitation of the bisphosphonates (pamidronate and 6-amino-1-hydroxypentilidene-bisphosphonate, used as internal standard) with calcium phosphate. After centrifugation the precipitate is redissolved in hydrochloric acid, followed by a second precipitation. Then the bisphosphonates are dissolved in ethylenediaminetetraacetic acid, derivatized with fluorescamine, and separated by high-performance liquid chromatography. Using fluorescence detection, the limit of quantitation for pamidronate was 0.8 mumol/l in plasma and 0.7 mumol/l in urine.     

Comparative protein modeling of 1-deoxy-D-xylulose-5-phosphate reductoisomerase enzyme from Plasmodium falciparum: a potential target for antimalarial drug discovery

Plasmodium falciparum 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Pf-DXR) is a potential target for antimalarial chemotherapy. The three-dimensional model (3D) of this enzyme was determined by means of comparative modeling through multiple alignment followed by intensive optimization, minimization, and validation. The resulting model demonstrates a reasonable topology as gauged from the Ramachandran plot and acceptable three-dimensional structure compatibility as assessed by the Profiles-3D score. The modeled monomeric subunit consists of three domains: (1) N-terminal NADPH binding domain, (2) connective or linker domain (with most of the active site residues located in this domain), and (3) a C-terminal domain. This structure proved to be consistent with known DXR crystal structures from other species. The predicted active site compared favorably with those of the templates and appears to have an active site with a highly conserved architecture. Additionally, the model explains several site-directed mutagenesis data. Besides using several protein structure-checking programs to validate the model, a set of known inhibitors of DXR were also docked into the active site of the modeled Pf-DXR. The docked scores correlated reasonably well with experimental pIC50 values with a regression coefficient (R2) equal to 0.84. Results of the current study should prove useful in the early design and development of inhibitors by either de novo drug design or virtual screening of large small-molecule databases leading to development of new antimalarial agents.     

Synthesis of two Novel 2-Aminocyclopropylidene-1,1-bisphosphonates

The synthesis of tetraethyl aminocyclopropylidene-1,1-bisphosphonate 1 and tetraethyl 2-(aminométhyl)cyclopropylidene-1,1-bisphosphonate 2 are described. The key steps include Michael addition, cyclisation and Curtius reaction for compound 1 and cyclisation, azide nucleophilic substitution and Staudinger reaction for 2.     

Transformation from a low-dimensional framework to a high-dimensional architecture based on different metal ions: syntheses, structures, and photoluminescences

Five novel metal pamidronates (3-ammonium-1-hydroxypropylidene-1,1-bisphosphonate, APD) formulated as Ni2(C3NH10P2O7)4.4H2O (1), M(C3NH9P2O7).H2O (M = Co (2), Mn (3), Zn (4)) and Cu3(C3NH8P2O7)2.2H2O (5) have been hydrothermally synthesized under similar conditions. Compound 1 is a molecular binuclear nickel cluster. Compounds 2 and 3 exhibit similar one-dimensional ladderlike structures. Compound 4 possesses a novel two-dimensional gridlike framework. Compound 5 shows an unusual three-dimensional architecture, in which two-dimensional layers with a parquet motif are pillared by {CuO4} planar squares. Different dinuclear secondary building units (SBUs) are observed in compounds 1-5, depending on the different coordination modes of APD. They also exhibit different photoluminescence properties.     

Synthesis and Structure of Dinitrosulfodienes of the Thiolene 1,1-Dioxide Series

A synthesis of previously unknown rigidly fixed heterocyclic structures, dinitrosulfodienes of the thiolene 1,1-dioxide series, was developed, and their structure was studied. The geometry and structural parameters of 3-methyl-4-nitro-2-[nitro(phenyl)methylene]-3-thiolene 1,1-dioxide were determined by X-ray diffraction.     

A novel mercapto-bisphosphonate as an efficient anticalcification agent for bioprosthetic tissues

The synthesis of 2-(2-mercaptoethylamino)ethylidene-1,1-bisphosphonic acid (2) is reported (overall yield >90%), via nucleophilic addition of cystamine to vinylidene-bisphosphonic acid (1) followed by reduction of disulfide bonds with Me₃P. Reaction of 1 with cysteamine forms the isomeric 2-(2-aminoethylthio)ethylidene-1,1-bisphosphonate (3) in an almost quantitative yield. Thiol groups of 2 in water at pH 7 react with epoxy rings more than 30 times faster compared to the known 2-mercaptoethylidene-1,1-bisphosphonate. Elimination of the thiol group is observed as a side-reaction in the reduction of disulfides with phosphines. Stabilization of bioprosthetic tissues with triglycidylamine in the presence of 2 results in covalent immobilization of 2 via an epoxy-SH reaction; this inhibits the long-term calcification of bioprosthetic heart valve tissues to almost undetectable levels.     

An efficient synthesis of 2-Aminoethylidene-1,1-Bisphosphonates derivatives via Michael addition reaction

A facile, rapid and cheap synthetic strategy towards a wide range of novel 2-aminoethylidene-1,1-bisphosphonate derivatives was developed through the Michael addition reaction of various aromatic amines, aromatic amides as well as nucleoside analogues with tetraethyl ethenylidene-1,1-bisphosphonate. All the newly obtained compounds were characterized by ¹H, ³¹P, ¹³C NMR spectroscopy, IR and HR MS.     

A new route to coordination complexes of nitroxyl (HN=O) via insertion reactions of nitrosonium triflate with transition-metal hydrides

Nitrosonium triflate reacts with cold methylene chloride solutions of mer,trans-ReH(CO)3(PPh3)2 (1) with 1,1-insertion of NO+ into the Re-H bond to give the orange nitroxyl complex [mer,trans-Re(NH=O)(CO)3(PPh3)2][SO3CF3] (3) in 86% isolated yield. Use of [NO][PF6] or [NO][BF4] gives analogous insertion products at low temperature, which decompose on warning to ambient temperature to the fluoride complex mer,trans-ReF(CO)3(PPh3)2 (4). A related 1,1-insertion is observed in the reaction of 1 with [PhN2][PF6] in acetone that affords the yellow-orange phenyldiazene salt [mer,trans-Re(NH=NPh)(CO)3(PPh3)2][PF6] (2), which has been characterized by X-ray crystallographic methods. The methyl derivative mer,trans-Re(CH3)(CO)3(PPh3)2 (5) also undergoes a 1,1-insertion reaction with [NO][SO3CF3] to give the nitrosomethane adduct [mer,trans-Re{N(CH3)=O}(CO)3(PPh3)2][SO3CF3] (6) as red crystals in 75% yield. The nitroxyl complex [cis,trans-OsBr(NH=O)(CO)2(PPh3)2][SO3CF3] (8) can be similarly prepared as orange crystals in 52% yield by reaction of cis,trans-OsHBr(CO)2(PPh3)2 (7) with [NO][SO3CF3] in cold methylene chloride solution.     

Crystal and molecular structures of four model compounds for liquid crystal dimers with a methylene spacer of various lengths

The crystal and molecular structures of four model compounds for liquid crystal dimers namely, 4,4-[octyl]bis-acetophenone (B(AcP)8), 4,4-[heptyl]bis-acetophenone (B(AcP)7), 4,4-[hexyl]bis-acetophenone (B(AcP)6), and 1,1-(1,6-hexyldion)bis-benzene (DP6D), have been determined in order to gain an insight into observed differences in the textures of liquid crystalline phases of compounds with odd and even methylene spacers. All four compounds exhibit extended conformations with an all-trans conformation of the methylene chain but a twist between phenyl rings of about 125°, except DP6D for which the benzene groups lie in plane with the methylene chain. Half a molecule is necessary to represent the asymmetric unit of compounds with even numbers n of methylene groups in the spacer and belong to centrosymmetric space groups. The model compound with an odd value of n is non-centrosymmetric and shows another type of packing arrangement which may cause different textures and behaviour for dimesogenic compounds in the liquid crystalline state.     

Differentiation of Constitutional Isomer of 2,2a,3,4-Tetrahydro- 4-methyl-2a-phenyl-2- （thiophen-2-yl）- 1H-azeto [-2,1-d] [- 1,51benzothiazepin-1-one-5-oxide and Fragmentations of 2,3-Dihydro-2,4-diphenyl-1,5-benzothiazepine-l-oxide／- 1,1-d

Mass spectrometric behaviour of 2,2a, 3,4-tetrahydro-4-methyl-2a-phenyl-2- (thiophen-2-yl)- 1H-azeto [-2,1-d-J1-1,5-]benzothiazepin-l-one-5-oxide and 2,3-dihydro-2,4-diphenyl-1,5-benzothiazepine-l-oxide/-1,1-dioxide have been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. The monooxide derivatives showed a tendency to eliminate an alkene or an oxygen atom. 1H-Azeto[-2,1-d][1,5]benzothiazepin-1-one-5-oxide could also eliminate the thiophen- 2-ylketene molecule via a reverse [-2 q- 2 ~ cycloaddition. 2,3-Dihydro-2,4-diphenyl- 1,5-benzothiazepine-1-oxide/-1, 1-dioxide could eliminate SO2 or SO, respectively. The structure of 2,2a, 3, 4-tetrahydro-4-methyl-2a-phenyl-2- (thiophen-2-yl)-1H-azeto 1-2,1-d-] [1,5 -] benzothiazepin-1-one-5-oxide was identified on the basis of its fragmentation. The identification was supported by the fragmentations of model compound, 2,3-dihydro-2,4-diphenyl-1,5-benzothiazepine-1-oxide/-1,1-dioxide.     

Synthesis of N-Substituted phosphoramidic acid esters as “reverse” fosmidomycin analogues

An efficient synthetic pathway to a series of novel “reverse” fosmidomycin analogues has been developed, commencing from substituted benzylamines. In these analogues, the fosmidomycin hydroxamate moiety is reversed and the tetrahedral methylene carbon adjacent to the phosphonate moiety is replaced by a nitrogen atom bearing different benzyl groups. The resulting phosphonate esters were designed as potential antimalarial “pro-drugs”.     

Scope and limitations of the double [4+3]-cycloadditions of 2-oxyallyl cations to 2,2'-methylenedifuran and derivatives

The reactivity of various 2-oxyallyl cations toward 2,2'-methylenedifuran (1b), 2,2'-(hydroxymethyl)difuran (1c), 2,2'-(trimethylsilylmethylene)difuran (1d), and di(2-furyl)methanone (1e) has been explored. Difuryl derivatives 1c, 1d, and 1e refused to undergo formal double [4+3]-cycloadditions. Conditions have been found to convert 1b into meso-1,1'-methylenedi[(1R,1'S,5S,5'R)- (3) and (+/-)-1,1'-methylenedi[(1RS,1'SR,5SR,5'RS)-8-oxabicyclo[3.2.1]oct-6-en-3-one] (4) that do not require CF(3)CH(OH)CF(3) as solvent. High yields of meso-1,1'-methylenedi[(1R,1'S,2S,2'R,4R,4'S,5S,5'R)- (5) and (+/-)-1,1'-methylenedi[(1RS,1'RS,2SR,2'SR,4RS,4'RS,5SR,5'SR)-2,4-dimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one] (6) have been obtained when 1b was reacted with 2,4-dibromopentan-3-one (7h) and NaI/Cu.     

Asymmetric platinum group metal-catalyzed carbonyl-ene reactions: carbon-carbon bond formation versus isomerization

A comparative study of the carbonyl-ene reaction between a range of 1,1'-disubstituted or trisubstituted alkenes and ethyl trifluoropyruvate catalyzed by Lewis acid-platinum group metal complexes of the type [M{(R)-BINAP}]2+ (M = Pt, Pd, Ni; BINAP is 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) revealed subtle but significant differences in their reactivity. For instance, the palladium-based Lewis acid [Pd{(R)-BINAP}]2+ catalyzes the ene reaction between methylene cycloalkane to afford the expected alpha-hydroxy ester in good yield and excellent diastereo- and enantioselectivity. In contrast, under the same conditions, the corresponding [M{(R)-BINAP}]2+ (M = Pt, Ni) catalyzes isomerization of methylene cycloalkane and the ene reaction of the resulting mixture of methylene cycloalkane and 1-methylcycloalkene at similar rates to afford a range of -hydroxy esters in high regioselectivity, good diastereoselectivity, and good to excellent enantioselectivity. In addition, [Pt{(R)-BINAP}]2+ also catalyzes postreaction isomerization of the ene product as well as consecutive ene reactions to afford a double carbonyl-ene product. The sense of asymmetric induction has been established by single-crystal X-ray crystallography, and a stereochemical model consistent with the formation of (S)-configured -hydroxy ester has been proposed; the same model also accounts for the observed exo-diastereoselectivity as well as the level of diastereoselectivity.