Phosphinic acid pseudopeptides analogous to glutamyl-gamma-glutamate: synthesis and coupling to pteroyl azides leads to potent inhibitors of folylpoly-gamma-glutamate synthetase

Phosphinic acid-based inhibitors of tubulin polyglycylation

Tubulin polyglycylation is a posttranslational modification that occurs primarily on the axonemes of flagella and cilia and has been shown to be essential for proper sperm motility. Inhibitors of both the initiase and elongase ligases (TTLL8 and TTLL10) are shown to inhibit tubulin glycylation in the low micromolar range.

A new type of heterogeneous catalysis strategy for organic reactions: Ugi-3CR catalyzed by highly stable MOFs with exposed carboxyl groups

A mild and highly efficient Ugi-3CR using a novel Cu-COOH@MOF-6 as the catalyst has been developed, which provides facile access to α-amino amides. The recycling test and XRD images showed that the catalytic system has good stability and recyclability.

Progress and perspectives on directing group-assisted palladium-catalysed C-H functionalisation of amino acids and peptides

Peptide modifications can unlock a variety of compounds with structural diversity and abundant biological activity. In nature, peptide modifications, such as functionalisation at the side-chain position of amino acids, are performed using post-translational modification enzymes or incorporation of unnatural amino acids. However, accessing these modifications remains a challenge for organic chemists. During the past decades, selective C-H activation/functionalisation has attracted considerable attention in synthetic organic chemistry as a pathway to peptide modification. Various directing group strategies have been discovered that assist selective C-H activation. In particular, bidentate directing groups that enable tuneable and reversible coordination are now recognised as one of the most efficient methods for the site-selective C-H activation and functionalisation of numerous families of organic compounds. Synthetic peptide chemists have harnessed bidentate directing group strategies for selective functionalisation of the β- and γ-positions of amino acids. This method has been expanded and recognised as an effective device for the late stage macrocyclisation and total synthesis of complex peptide natural products. In this review, we discuss various β-, γ-, and δ-C(sp³)-H bond functionalisation reactions of amino acids for the formation of C-X bonds with the aid of directing groups and their application in late-stage macrocyclisation and the total synthesis of complex peptide natural products.

Nonradioactive Cell Assay for the Evaluation of Modular Prostate-Specific Membrane Antigen Targeting Ligands via Inductively Coupled Plasma Mass Spectrometry

The development of novel prostate-specific membrane antigen (PSMA)-targeted radioactive theranostic agents is currently limited to facilities capable of working with high-energy radioisotopes. Even preselection of lead structures in vitro relies mostly on radioactive assays with PSMA(+) LNCaP and PSMA(-) PC-3 cells. Assays utilizing radioisotopes are time consuming, costly, and limit discovery to a small group of scientists with special facilities. Nonradioactive alternatives are therefore needed in the field. In this paper, we describe an inductively coupled plasma mass spectrometry (ICP-MS)-based method for the evaluation of PSMA-targeting ligands conjugated to DOTA-chelates of Europium. This method is based on LNCaP and PC-3 cells and has been validated with the well-established targeting ligand PSMA-617.

Phosphinic acid-based inhibitors of tubulin polyglutamylases

Tubulin is subject to a reversible post-translational modification involving polyglutamylation and deglutamylation of glutamate residues in its C-terminal tail. This process plays key roles in regulating the function of microtubule associated proteins, neuronal development, and metastatic progression. This study describes the synthesis and testing of three phosphinic acid-based inhibitors that have been designed to inhibit both the glutamylating and deglutamylating enzymes. The compounds were tested against the polyglutamylase TTLL7 using tail peptides as substrates (100 μM) and the most potent inhibitor displayed an IC₅₀ value of 150 μM. The incorporation of these compounds into tubulin C-terminal tail peptides may lead to more potent TTLL inhibitors.

Direct and facile synthesis of acyl azides from carboxylic acids using the trichloroisocyanuric acid–triphenylphosphine system

A mild, efficient, and practical method for the one-step synthesis of acyl azides from carboxylic acids using a safe and inexpensive mixed reagent, trichloroisocyanuric acid–triphenylphosphine, is described.

Characterisation of the bifunctional dihydrofolate synthase-folylpolyglutamate synthase from Plasmodium falciparum; a potential novel target for antimalarial antifolate inhibition

Unusually for a eukaryote, the malaria parasite Plasmodium falciparum expresses dihydrofolate synthase (DHFS) and folylpolyglutamate synthase (FPGS) as a single bifunctional protein. The two activities contribute to the essential pathway of folate biosynthesis and modification. The DHFS activity of recombinant PfDHFS–FPGS exhibited non-standard kinetics at high co-substrate (glutamate and ATP) concentrations, being partially inhibited by increasing concentrations of its principal substrate, dihydropteroate (DHP). Binding of DHP to the catalytic and inhibitory sites exhibited dissociation constants of 0.50 μM and 1.25 μM, respectively. DHFS activity measured under lower co-substrate concentrations, where data fitted the Michaelis–Menten equation, yielded apparent K_m values of 0.88 μM for DHP, 22.8 μM for ATP and 5.97 μM for glutamate. Of the substrates tested in FPGS assays, only tetrahydrofolate (THF) was efficiently converted to polyglutamylated forms, exhibiting standard kinetics with an apparent K_m of 0.96 μM; dihydrofolate, folate and the folate analogue methotrexate (MTX) were negligibly processed, emphasising the importance of the oxidation state of the pterin moiety. Moreover, MTX inhibited neither DHFS nor FPGS, even at high concentrations. Conversely, two phosphinate analogues of 7,8-dihydrofolate that mimic tetrahedral intermediates formed during DHFS- and FPGS-catalysed glutamylation were powerfully inhibitory. The K_i value of an aryl phosphinate analogue against DHFS was 0.14 μM and for an alkyl phosphinate against FPGS 0.091 μM, with each inhibitor showing a high degree of specificity. This, combined with the absence of DHFS activity in humans, suggests PfDHFS–FPGS might represent a potential new drug target in the previously validated folate pathway of P. falciparum.

Inhibition of human folylpolyglutamate synthetase by diastereomeric phosphinic acid mimics of the tetrahedral intermediate

Phosphorus-containing pseudopeptides, racemic at the C-terminal alpha-carbon, are potent mechanism-based inhibitors of folylpolyglutamate synthetase (FPGS). They are mimics of the tetrahedral intermediate postulated to form during FPGS-catalyzed biosynthesis of poly(gamma-l-glutamates). In the present paper, the FPGS inhibitory activity of each diastereomer coupled to three heterocycles is reported. The high R(f) pseudopeptide containing the 5,10-dideazatetrahydropteroyl (DDAH(4)Pte) heterocycle is most potent (K(is) = 1.7 nM). While the heterocyclic portion affects absolute FPGS inhibitory potency, the high R(f) species is more potent in each pair containing the same heterocycle. This species presumably has the same stereochemistry as the natural folate polyglutamate, i.e., (l-Glu-gamma-l-Glu). Unexpectedly, the low R(f) (presumed l-Glu-gamma-d-Glu) species are only slightly less potent (<30-fold) than their diastereomers. Further study of this phenomenon comparing l-Glu-gamma-l-Glu and l-Glu-gamma-d-Glu dipeptide-containing FPGS substrates shows that <1% contamination of commercial d-Glu precursors by l-Glu may give misleading information if l-Glu-gamma-l-Glu substrates have low K(m) values.

Multivalent scaffolds for affinity maturation of small molecule cell surface binders and their application to prostate tumor targeting

Adamantane scaffolds for affinity maturation of prostate cancer specific ligands of low molecular mass are described. These scaffolds are modular and can be used for conjugation of up to three ligands and an additional effector molecule by standard peptide coupling techniques. The potential of the scaffolds is demonstrated with the multimerization of GPI 1, a prostate cancer specific small molecule. A detailed study of multimerized GPI conjugates with near-infrared fluorophores and their binding properties to different prostate cancer cell lines shows the specific binding of these conjugates to cell types positive for prostate specific membrane antigen (PSMA). We demonstrate that these conjugates allow the sensitive imaging of prostate cancer cells with NIR methodology and suggest that our adamantane scaffolds might be generally useful for affinity maturation of small molecules targeting cell surface epitopes.

ATP-dependent ligases in trypanothione biosynthesis--kinetics of catalysis and inhibition by phosphinic acid pseudopeptides

Glutathionylspermidine is an intermediate formed in the biosynthesis of trypanothione, an essential metabolite in defence against chemical and oxidative stress in the Kinetoplastida. The kinetic mechanism for glutathionylspermidine synthetase (EC 6.3.1.8) from Crithidia fasciculata (CfGspS) obeys a rapid equilibrium random ter-ter model with kinetic constants K_GSH = 609 μm, K_Spd = 157 μm and K_ATP = 215 μm. Phosphonate and phosphinate analogues of glutathionylspermidine, previously shown to be potent inhibitors of GspS from Escherichia coli, are equally potent against CfGspS. The tetrahedral phosphonate acts as a simple ground state analogue of glutathione (GSH) (K_i ∼ 156 μm), whereas the phosphinate behaves as a stable mimic of the postulated unstable tetrahedral intermediate. Kinetic studies showed that the phosphinate behaves as a slow-binding bisubstrate inhibitor [competitive with respect to GSH and spermidine (Spd)] with rate constants k₃ (on rate) = 6.98 × 10⁴m⁻¹·s⁻¹ and k₄ (off rate) = 1.3 × 10⁻³ s⁻¹, providing a dissociation constant K_i = 18.6 nm. The phosphinate analogue also inhibited recombinant trypanothione synthetase (EC 6.3.1.9) from C. fasciculata, Leishmania major, Trypanosoma cruzi and Trypanosoma brucei with K_i^app values 20–40-fold greater than that of CfGspS. This phosphinate analogue remains the most potent enzyme inhibitor identified to date, and represents a good starting point for drug discovery for trypanosomiasis and leishmaniasis.

Structural basis of interactions between human glutamate carboxypeptidase II and its substrate analogs

Human glutamate carboxypeptidase II (GCPII) is involved in neuronal signal transduction and intestinal folate absorption by means of the hydrolysis of its two natural substrates, N-acetyl-aspartyl-glutamate and folyl-poly-gamma-glutamates, respectively. During the past years, tremendous efforts have been made toward the structural analysis of GCPII. Crystal structures of GCPII in complex with various ligands have provided insight into the binding of these ligands, particularly to the S1' site of the enzyme. In this article, we have extended structural characterization of GCPII to its S1 site by using dipeptide-based inhibitors that interact with both S1 and S1' sites of the enzyme. To this end, we have determined crystal structures of human GCPII in complex with phosphapeptide analogs of folyl-gamma-glutamate, aspartyl-glutamate, and gamma-glutamyl-glutamate, refined at 1.50, 1.60, and 1.67 A resolution, respectively. The S1 pocket of GCPII could be accurately defined and analyzed for the first time, and the data indicate the importance of Asn519, Arg463, Arg534, and Arg536 for recognition of the penultimate (i.e., P1) substrate residues. Direct interactions between the positively charged guanidinium groups of Arg534 and Arg536 and a P1 moiety of a substrate/inhibitor provide mechanistic explanation of GCPII preference for acidic dipeptides. Additionally, observed conformational flexibility of the Arg463 and Arg536 side chains likely regulates GCPII affinity toward different inhibitors and modulates GCPII substrate specificity. The biochemical experiments assessing the hydrolysis of several GCPII substrate derivatives modified at the P1 position, also included in this report, further complement and extend conclusions derived from the structural analysis. The data described here form an a solid foundation for the structurally aided design of novel low-molecular-weight GCPII inhibitors and imaging agents.

Design, synthesis, and metal binding of novelPseudo- oligopeptides containing two phosphinic acid groups

Phosphinic compounds have potential as amide-bond mimetics in the development of novel peptidomimetics, enzyme inhibitors, and metal-binding ligands. Novel pseudo-oligopeptides with two phosphinic acid groups embedded in the peptide backbone serving as amide-bond surrogates, Psi[P(O,OH)--CH(2)], were targeted. A series of linear and cyclic pseudo-oligopeptides with two phosphinic acid groups arrayed at different positions in the peptide sequence were designed, including Ac--Phe--{(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly}(2)--NH(2) (P2), Ac--NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--NH(2) (P3), Ac--NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe--Phe--(R,S) --AlaPsi[P(O,OH)--CH(2)]Gly--NH(2) (P4), cyclo{NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe}(2) (P5), and cyclo[NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe--Phe](2) (P6). They were synthesized via conventional Fmoc chemistry on solid support utilizing Fmoc-protected phosphinic acid-containing pseudo-dipeptide fragment, i.e. Fmoc--(R,S)--AlaPsi[P(O,OCH(3))--CH(2)]Gly--OH. The pseudo-peptides containing two phosphinic acid groups exhibited the highest binding affinity and selectivity for Fe(III) among the 10-metal ions screened by ESI-MS analysis--Cu(II), Zn(II), Co(II), Ni(II), Mn(II), Fe(II), Fe(III), Al(III), Ga(III), and Gd(III). P4 and P6 with 11-atom linkages between the two phosphinic acids preferred intramolecular metal binding to form 1:1 ligand/metal complexes. As revealed by competition experiments, P4 showed the highest relative binding affinity among the six compounds tested. Noteworthy, P4 also showed higher relative binding affinity than similar dihydroxamate-containing pseudo-peptides reported previously. The novel structural prototype and facile synthesis along with selective and potent Fe(III) binding strongly suggest that pseudo-peptides containing the two or more phosphinic groups as amide-bond surrogates deserve further exploration in medicinal chemistry.

Progress in the discovery and development of glutamate carboxypeptidase II inhibitors

During the past 10 years, substantial progress has been made in the discovery and development of small molecule glutamate carboxypeptidase II (GCP II) inhibitors. These inhibitors have provided the necessary tools to investigate the physiological role of GCP II as well as the potential therapeutic benefits of its inhibition in neurological disorders of glutamatergic dysregulation. This review article details key GCP II inhibitors discovered in the last decade and important findings from preclinical and clinical studies.

Asymmetric Synthesis of 2-Alkyl-3-phosphonopropanoic Acids via P−C Bond Formation and Hydrogenation

Allylic acetates, formed by the acetylation of Baylis Hillman adducts, undergo addition of phosphorus nucleophiles to give stereoselectively the Z-unsaturated esters. TFA cleavage of the tert-butyl ester and asymmetric hydrogenation of the unsaturated acid yields the phosphono alkyl propanoic acid moiety, commonly found in phosphonate- and phosphinate-based enzyme inhibitors.

Synthesis of p-Aminophenyl Aryl H-Phosphinic Acids and Esters via Cross-Coupling Reactions: Elaboration to Phosphinic Acid Pseudopeptide Analogues of Pteroyl Glutamic Acid and Related Antifolates

The synthesis of suitably protected p-aminophenyl H-phosphinic acids and esters from the corresponding para-substituted aryl halides has been accomplished via the Pd-catalyzed cross-coupling reaction of anilinium hypophosphite, either in the absence or presence of a tetraalkyl orthosilicate, to provide the free H-phosphinic acid or the corresponding ester, respectively. Subsequent conjugate addition of either a PIII species or phosphorus anion, generated in situ from either the free H-phosphinic acid or ester, to a 2-methylene glutaric acid ester provided the aryl phosphinic acid analogue of p-aminobenzoyl glutamic acid. Alkylation of these suitably protected p-aminophenyl phosphinic acid esters with a 6-(bromomethyl)pteridine or the corresponding (bromomethyl)pyridopyrmidine, followed by hydrolytic removal of protecting groups, provided the target aryl phosphinic acid analogues of folic acid and related antifolates. Alternatively, for the synthesis of the folate or 5-deazafolate analogues on a slightly larger scale, reductive amination with either N2-acetyl or N2-pivaloyl-6-formylpterin or the corresponding formylpyridopyrmidine and the same suitably protected p-aminophenyl phosphinic acid esters, followed by removal of protecting groups, is preferred. In the course of this research, it was observed that the nucleophilicity of both the aniline nitrogen and various PIII species derived from p-aminophenyl phosphinic acid derivatives is significantly reduced compared to that of the unsubstituted counterpart.

Double dearomatization of bis(diphenylphosphinamides) through anionic cyclization. A facile route of accessing multifunctional systems with antitumor properties

The sequential one-pot double dearomatization of bis(N-benzyl-P,P-diphenylphosphinamides) via anionic cyclization is described for the first time. Protonation and alkylation of the dearomatized dianions provide bis(tetrahydro-2,1-benzazaphospholes) in good yield and with very high regio- and stereocontrol. Acid-catalyzed methanolysis of the bisheterocycles affords bis(methyl gamma-aminophosphinates) stereospecifically. The doubly phosphorylated systems proved to be active against a series of cancer cell lines.

Alkylation of H-phosphinate esters under basic conditions

An efficient and general procedure was developed for the direct alkylation of H-phosphinate esters with LHMDS at low temperature. The simplicity of the reaction allows the use of various H-phosphinate esters and takes place with a wide range of electrophiles. The approach can be employed to access some GABA analogues or precursors to GABA analogues. The isolated yields are moderate to good. This is the first report of an alkylation with a secondary iodide or a primary chloride.

An HPLC/mass spectrometry platform for the development of multimodality contrast agents and targeted therapeutics: prostate-specific membrane antigen small molecule derivatives

The production of disease-targeted agents requires the covalent conjugation of a targeting molecule with a contrast agent or therapeutic, followed by purification of the product to homogeneity. Typical targeting molecules, such as small molecules and peptides, often have high charge-to-mass ratios and/or hydrophobicity. Contrast agents and therapeutics themselves are also diverse, and include lanthanide chelates for MRI, (99m)Tc chelates for SPECT, (90)Y chelates for radiotherapy, (18)F derivatives for PET, and heptamethine indocyanines for near-infrared fluorescent optical imaging. We have constructed a general-purpose HPLC/mass spectrometry platform capable of purifying virtually any targeted agent for any modality. The analytical sub-system is composed of a single dual-head pump that directs mobile phase to either a hot cell for the purification of radioactive agents or to an ES-TOF MS for the purification of nonradioactive agents. Nonradioactive agents are also monitored during purification by ELSD, absorbance and fluorescence. The preparative sub-system is composed of columns and procedures that permit rapid scaling from the analytical system. To demonstrate the platform's utility, we describe the preparation of five small molecule derivatives specific for prostate-specific membrane antigen (PSMA): a gadolinium derivative for MRI, indium, rhenium and technetium derivatives for SPECT, and an yttrium derivative for radiotherapy. All five compounds are derived from a highly anionic targeting ligand engineered to have a single nucleophile for N-hydroxysuccinimide-based conjugation. We also describe optimized column/mobile phase combinations and mass spectrometry settings for each class of agent, and discuss strategies for purifying molecules with extreme charge and/or hydrophobicity. Taken together, our study should expedite the development of disease-targeted, multimodality diagnostic and therapeutic agents.

A stereoselective synthesis of phosphinic acid phosphapeptides corresponding to glutamyl-gamma-glutamate and incorporation into potent inhibitors of folylpoly-gamma-glutamyl synthetase

Radical addition of H3PO2 to N-/C-protected vinyl glycine led to the corresponding H-phosphinic acid in excellent yield. The non-nucleophilic H-phosphinic acid was converted to a nucleophilic P(III) species, RP(OTMS)2, which was used in two approaches to the target phosphinic acid containing pseudopeptide. New methodology was developed that led to excellent yields in the reaction of RP(OTMS)2 with unactivated electrophiles, including an acyclic homoallylic bromide. However, en route to the target pseudopeptide, Arbuzov reaction of RP(OTMS)2 with a cyclic homoallylic bromide, (R)-3-(bromomethyl)-cyclopent-1-ene, led to a rearranged allylic phosphinic acid rather than the desired homoallylic derivative, a putative glutarate surrogate. Conjugate addition of RP(OTMS)2 to alpha-methylene glutarate containing a chiral auxiliary resulted in only modest diastereoselectivity. Purification by flash chromatography provided protected derivatives of both diastereomers of the pseudopeptide. Following global deprotection, coupling of (S)-H-Glu-gamma-[Psi(P(O)(OH)(CH2))]-(S)-Glu-OH and (S)-H-Glu-gamma-[Psi(P(O)(OH)(CH2))]-(R)-Glu-OH to (4-amino-4-deoxy-10-methyl)pteroyl azide led to the target compounds for biochemical study as inhibitors of the ATP-dependent ligase, folylpoly-gamma-glutamate synthetase.

Prodrug forms of N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate, a potent inhibitor of folylpoly-gamma-glutamate synthetase: synthesis and hydrolytic stability

Ester prodrugs of the phosphinate pseudopeptide N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate (1a) were synthesized. H-phosphinic acids derived from N-Cbz vinyl glycine esters were converted to the desired pseudopeptides by Michael addition to alpha-methyleneglutarate esters. Pivaloyloxymethyl (POM) ester moieties were incorporated in both the N-terminal and C-terminal fragments prior to formation of either C-P bond. N-Alkylation of the corresponding amides derived from p-(N-methyl)aminobenzoic acid with 2,4-diamino-6-(bromomethyl)pteridine gave the target compounds. POM esters of methotrexate and the corresponding gamma-glutamyl conjugate were also synthesized using the same strategy. All prodrugs were evaluated in Chinese hamster ovary cells. Although the pseudopeptide prodrugs were ineffective, prodrugs of methotrexate and the corresponding gamma-glutamyl conjugate were equipotent with the parent compounds. Stability of the prodrugs was investigated in both phosphate buffer and cell line medium to provide a rationale for the observed biological data.

Regioselective synthesis of alpha-methyl 2-methyleneglutarate via a novel lactonization-elimination rearrangement

[reaction: see text] A facile route to the alpha-methyl ester of 2-methyleneglutarate via a three-step sequence from 3-hydroxymethylcyclopentene is described. Regioselective formation of the monoacid from a diester precursor proceeds via a novel fluoride-mediated, tandem deprotection/rearrangement of O-silyl 2-(hydroxymethyl)dimethylglutarate.

Enzyme inhibitors as chemical tools to study enzyme catalysis: rational design, synthesis, and applications

Carefully designed molecules that are intimately related to the reaction mechanism of enzymes are often highly selective and potent inhibitors that serve as extremely useful chemical probes for understanding the reaction mechanism and structure of enzymes. This article describes the design, synthesis, and applications of specific inhibitors of two mechanistically distinct groups of enzymes, ATP-dependent amide ligases and Ser- and Thr-hydrolases. Our strategy is based on the premise that stable analogues of the transition state (transition-state analogues) are highly potent inhibitors that serve as good mechanistic probes, and that a key structure of a good inhibitor of one enzyme is also utilized for the inhibitors of other enzymes that share the same chemistry in their catalyzed reactions, irrespective of the degree of structural similarity and evolutionary link between the enzymes. According to these principles, we designed and synthesized a series of phosphinate- and sulfoximine-based transition-state analogue inhibitors of glutathione synthetase, gamma-glutamylcysteine synthetase and asparagine synthetase. For the second group of enzymes, we synthesized a gamma-monofluorophosphono glutamate analogue for mechanism-based affinity labeling of gamma-glutamyltranspeptidase and fluorescent phosphonic acid esters for the active-site titration of lipase. These inhibitors were used successfully as ligands for detailed kinetic analyses, X-ray crystallography, and mass analysis of the enzymes to identify the key amino acid residues responsible for catalysis and substrate recognition in the transition state.

High-affinity Near-infrared Fluorescent Small-molecule Contrast Agents for In Vivo Imaging of Prostate-specific Membrane Antigen

Surgical resection remains a definitive treatment for prostate cancer. Yet, prostate cancer surgery is performed without image guidance for tumor margin, extension beyond the capsule and lymph node positivity, and without verification of other occult metastases in the surgical field. Recently, several imaging systems have been described that exploit near-infrared (NIR) fluorescent light for sensitive, real-time detection of disease pathology intraoperatively. In this study, we describe a high-affinity (9 nM), single nucleophile-containing, small molecule specific for the active site of the enzyme PSMA. We demonstrate production of a tetra-sulfonated heptamethine indocyanine NIR fluorescent derivative of this molecule using a high-yield LC/MS purification strategy. Interestingly, NIR fluorophore conjugation improves affinity over 20-fold, and we provide mechanistic insight into this observation. We describe the preparative production of enzymatically active PSMA using a baculovirus expression system and an adenovirus that co-expresses PSMA and GFP. We demonstrate sensitive and specific in vitro imaging of endogenous and ectopically expressed PSMA in human cells and in vivo imaging of xenograft tumors. We also discuss chemical strategies for improving performance even further. Taken together, this study describes nearly complete preclinical development of an optically based small-molecule contrast agent for image-guided surgery.

Design, Synthesis, and Activity of Analogues of Phosphinothricin as Inhibitors of Glutamine Synthetase

A new group of potent inhibitors of glutamine synthetase was designed and synthesized. The X-ray structure of bacterial glutamine synthetase complexed with phosphinothricin was used for computer-aided structure-based design of the inhibitors, in which the methyl group of phosphinothricin was chosen as the modification site. Amino and hydroxyl moieties were introduced into the phosphinic acid portion of the lead molecule to interact with ammonium binding site in the active cleft of the enzyme. Designed compounds were synthesized in enantiomerically pure form analogous to l-glutamic acid. In vitro kinetic studies with Escherichia coli glutamine synthetase confirmed the biological activity of the designed inhibitors, which with K(i) values in the micromolar range (K(i) = 0.59 microM for the most potent compound 2) appear to be slightly weaker inhibitors or equipotent to phosphinothricin.

Synthesis of (6R)- and (6S)-5,10-dideazatetrahydrofolate oligo-gamma-glutamates: kinetics of multiple glutamate ligations catalyzed by folylpoly-gamma-glutamate synthetase

Folylpoly-gamma-glutamate synthetase (FPGS, EC 6.3.2.17) catalyzes the ATP-dependent ligation of glutamic acid to reduced folates including (6S)-5,6,7,8-tetrahydrofolate (H4PteGlu), as well as to anticancer drugs such as 5,10-dideaza-5,6,7,8-tetrahydrofolate ((6R)-DDAH4PteGlu1, (6R)-DDATHF, Lometrexol). Synthesis of unlabeled mono- and polyglutamates, DDAH4PteGlu(n) (6R, n = 1-6; 6S, n = 1-2), as well as (6R)-DDAH4Pte[14C]Glu1, was effected from (6R)- or (6S)-5,10-dideazatetrahydropteroyl azide and glutamic acid, H-Glu-gamma-Glu(n)-gamma-Glu-OH (n = 0-4), or [14C]glutamic acid, respectively. These compounds were evaluated as FPGS substrates to determine steady-state kinetic constants. Michaelis-Menten kinetics were observed for (6R)-DDAH4PteGlu1, the isomer corresponding to H(4)PteGlu, whereas marked substrate inhibition was observed for (6S)-DDAH4PteGlu(n) (n = 1-2) and (6R)-DDAH4PteGlu(n) (n = 2-5), but not (6R)-DDAH4PteGlu6. Multiple ligation of glutamate renders a quantitative analysis of these data difficult. However, approximate values of K(M) = 0.65-1.6 microM and K(I) = 144-417 microM for DDAH4PteGlu(n) were obtained using a simple kinetic model.

Synthesis and biological evaluation of alpha- and gamma-carboxamide derivatives of 10-CF3CO-DDACTHF

Structurally-related, but non-polyglutamylatable, derivatives of 10-CF3CO-DDACTHF (1), which incorporate L-glutamine (2) and L-isoglutamine (3) in place of L-glutamate, were prepared and evaluated as inhibitors of recombinant human (rh) GAR Tfase. While the L-glutamate alpha-carboxamide derivative 3 was much less effective as a rhGAR Tfase inhibitor (K(i) = 4.8 microM) and inactive in cellular functional assays, the gamma-carboxamide derivative 2 was found to be a potent and selective rhGAR Tfase inhibitor (K(i) = 0.056 microM) being only 4-fold less potent than 1 (K(i) = 0.015 microM). Moreover, 2 was effective in cellular functional assays exhibiting purine sensitive cytotoxic activity (IC50 = 300 nM, CCRF-CEM) only 20-fold less potent than 1 (IC50 = 16 nM), consistent with inhibition of de novo purine biosynthesis via selective inhibition of GAR Tfase. Like 1, 2 is transported into the cell by the reduced folate carrier. Unlike 1, the functional activity of 2 is not dependent upon FPGS polyglutamylation.

Copper(II) complexes of some N-substituted bis(aminomethyl)phosphinate ligands. An integrated EPR study of microspeciation and coordination modes by the two-dimensional simulation method

Copper(II) complexes of bis(aminomethyl)phosphinic acid (L1), bis(N-glycino-N-methyl)phosphinic acid (L2), bis(N-benzylglycino-N-methyl)phosphinic acid (L3), bis(l-prolino-N-methyl)phosphinic acid (L4) and bis(iminodicarboxymethyl-N-methyl)phosphinic acid (L5) were studied in aqueous solution by pH-potentiometric and electron paramagnetic resonance (EPR) spectroscopic methods. The EPR spectrum packages recorded at various ligand-to-metal concentration ratios and pH's were analyzed (after matrix rank analysis by the method of residual intensities as a complementary method) by the two-dimensional computer simulation method, which simultaneously determines the formation constants and the EPR parameters of the various (micro)species. L1 forms mono and bis complexes in different protonation states; for the other ligands, the mono complexes are always prevalent. For steric reasons, the formation of CuL is shifted to increasingly higher pH regions in the sequence L2, L3 and L4. CuLH was identified for L3, L4 and L5, and also CuLH(2) for L4 and L5. Cu(2)L(2) was found in small amounts for L3 and L4, while it predominates at pH>4 for L5. For L5, Cu(2)L(2)H(2) was also detected. For the ligands that form dimeric metal complexes in equimolar solution or at a ligand excess, Cu(2)L is formed at a metal ion excess. Ligation of the phosphinate O was suggested by indirect proofs in the protonated complexes of L1. For the ligands L2, L3 and L4, the copper(II) coordination in various species in different protonation states is reminiscent of that in the mono and bis complexes of simple amino acids. For the bis(aminomethyl)phosphinates, however, the cis positions of the amino groups in CuL are ensured by the structure of the ligand, and the isomers differ from each other in the (equatorial or axial) position of the second carboxylate group.

Synthesis of functionalized 1,4-cyclohexadienes through intramolecular anionic dearomatization of N-alkyl-N-benzyldiphenylphosphinamides. Insight into the reaction mechanism

A generalization of the intramolecular nucleophilic dearomatization-electrophilic alkylation reactions of N-alkyl-N-benzyldiphenylphosphinamide anions is presented. The process has been optimized by analyzing the effects of metalation and quench times, additives, the nature of the electrophiles used (MeI, CF(3)SO(3)Me, Me(3)O(+)BF(4)(-), AllylBr, PhCH(2)Br, BrCH(2)CO(2)Me, and RCH=O, where R = Ph, 4-Cl-C(6)H(4), 4-MeO-C(6)H(4), and (i)()Pr), and the alkyl substituent linked to the nitrogen of the phosphinamide. Both HMPA and DMPU act as catalysts. The latter proved to be much more efficient for obtaining high yields of substituted tetrahydrobenzo[c][1,2]-1lambda(5)-phospholes containing a 1,4-cyclohexadiene system with very high regio- and diastereoselectivity. Steric effects in the neighborhood of the benzylic anion tend to decrease the stereoselectivity of the anionic cyclization. The optimization study also served to shed light on the reaction mechanism of the dearomatization process by identifying several intermediate species and showing the reversibility of the anionic cyclization step as well as of the reaction with aldehydes.

Potent inhibition of human folylpolyglutamate synthetase by a phosphinic acid mimic of the tetrahedral reaction intermediate

A phosphorous-containing pseudopeptide folate analog (Valiaeva et al., J Org Chem 2001;66:5146-54) was designed to mimic the tetrahedral intermediate formed in the ATP-dependent reaction catalyzed by folylpolyglutamate synthetase (FPGS). This analog, methotrexate-phosphinate (MTX-phosphinate; 4-amino-4-deoxy-10-methylpteroyl-L-Glu-gamma-[psi(P(O)(OH)-CH(2))]glutarate), is a highly potent (K(is), 3.1+/-0.5 nM), competitive inhibitor of recombinant human cytosolic FPGS. Within experimental limits, FPGS inhibition was not time-dependent, and preincubation of FPGS, inhibitor, and ATP did not potentiate the inhibition. These results suggest that slow phosphorylation to produce a more potent inhibitor form is not involved. MTX-phosphinate was not growth inhibitory to human CCRF-CEM leukemia cells at 1 microM (70-fold above the concentration of MTX giving 50% growth inhibition), probably because of poor transport. Because of its exceedingly high potency as an FPGS inhibitor, MTX-phosphinate represents a lead structure from which cell-permeable analogs may be developed to test the hypothesis that FPGS inhibition is therapeutically efficacious.

Facile synthesis of alpha-substituted acrylate esters

Treatment of 5-monosubstituted Meldrum's acids with dimethylmethyleneimmonium iodide (Eschenmoser's iodide salt) in methanol gives alpha-substituted acrylate methyl esters in good yields. Easy access to 5-monosubstituted Meldrum's acids allowed us to synthesize a wide variety of alpha-substituted acrylate methyl esters. The reaction conditions are mild and tolerate many functional groups commonly used in organic synthesis; thus, this new method has potential as an alternative to conventional preparative methods for alpha-substituted acrylate esters.

Phosphonate and phosphinate analogues of N-acylated gamma-glutamylglutamate. potent inhibitors of glutamate carboxypeptidase II

Phosphonate and phosphinate analogues of N-acylated gamma-glutamylglutamate were tested for the ability to inhibit glutamate carboxypeptidase II (GCP II). All of the compounds inhibit GCP II with IC(50) values in the low nanomolar range. The comparison of the results to previously reported inhibitory studies of the same compounds toward folylpoly-gamma-glutamyl synthetase (FPGS) and gamma-glutamyl hydrolase (gamma-GH) provides insight into structural and mechanistic features of each enzyme. Potential utility of these compounds as diagnostic agents and probes to understand folate or antifolate poly-gamma-glutamates metabolism is also described.

Regio- and diastereoselective preparation of tetrahydrobenzo[c]-1-aza-2lambda(5)-phospholes through dearomatization cyclization of lithiated N-benzyl-N-alkyl(diphenyl)phosphinamides. Synthesis of gamma-(N-alkylamino)phosphinic acids

A study of the protonation of the cycloadducts derived from the dearomatization reaction of lithiated N-alkyl-N-benzyldiphenylphosphinamides has been carried out. The regio- and stereoselectivity of the process has been analyzed in terms of the size of the N-alkyl substituent, the acidity and size of the protonating reagent, and the cosolvent used. The optimization of these variables allowed the preparation of tetrahydrobenzo[c]-1-aza-2lambda(5)-phospholes containing a 1,3-cyclohexadiene or 1,4-cyclohexadiene system with moderate to excellent regio- and stereocontrol. The heterocycles were readily hydrolyzed, affording gamma-(N-alkylamino)diphenylphosphinic acids with the functionalities linked to a cyclohexadiene substructure.