Total synthesis of exigurin: the Ugi reaction in a hypothetical biosynthesis of natural products.

The first total synthesis of a marine natural product, exigurin, has been accomplished in 13 steps starting from (+)-menthone. The key intermediate (-)-10-epi-axisonitrile-3 was prepared by stereoselective intramolecular cyclopropanation followed by a cyclopropane ring opening reaction by the azide anion. The bioinspired Ugi reaction of (-)-10-epi-axisonitrile-3, formaldehyde, sarcosine and methanol successfully constructed the target exigurin in which its terpene and amino acid units were linked through an amide bond.

Synthesis and Biocompatibility Studies of New Iminodiacetic Acid Derivatives.

BACKGROUND: Iminodiacetic acid (IDA) derivatives can be used as ligands to form complexes with technetium, with potential application as hepatobiliary diagnostic agents. The aim of this study was to synthesize five novel IDA derivatives and to compare their effects on plasma haemostasis with clinically approved ligands for technetium complexation. METHODS: The influence of synthesized IDA derivatives on plasma haemostasis was evaluated spectrophotometrically by clot formation and lysis test (CL-test), coagulation assay, Prothrombin Time and Activated Partial Tromboplastin Time. The effects of the tested compounds on erythrocytes were assessed using haemolysis assays, microscopy and flow cytometry studies. RESULTS: Despite their significant influence on the kinetic parameters of the process of clot formation and fibrinolysis, the tested ligands, at potential diagnostic concentrations, did not alter the overall potential of clot formation and lysis (CLAUC). At potential diagnostic concentrations (0.4 µmol/mL) all the tested compounds showed no adverse effects on the membranes of RBCs (Red Blood Cells). CONCLUSION: IDA derivatives with methoxy substituents in aromatic ring, exert multidirectional effects on plasma haemostasis and should be considered safe as their significant impacts were mostly observed at 4 µmol/mL, which is about 10-fold higher than the theoretical plasma concentrations of these compounds.

Mechanistic studies into amine-mediated electrophilic arene borylation and its application in MIDA boronate synthesis.

Direct electrophilic borylation using Y(2)BCl (Y(2) = Cl(2) or o-catecholato) with equimolar AlCl(3) and a tertiary amine has been applied to a wide range of arenes and heteroarenes. In situ functionalization of the ArBCl(2) products is possible with TMS(2)MIDA, to afford bench-stable and easily isolable MIDA-boronates in moderate to good yields. According to a combined experimental and computational study, the borylation of activated arenes at 20 °C proceeds through an S(E)Ar mechanism with borenium cations, [Y(2)B(amine)](+), the key electrophiles. For catecholato-borocations, two amine dependent reaction pathways were identified: (i) With [CatB(NEt(3))](+), an additional base is necessary to accomplish rapid borylation by deprotonation of the borylated arenium cation (σ complex), which otherwise would rather decompose to the starting materials than liberate the free amine to effect deprotonation. Apart from amines, the additional base may also be the arene itself when it is sufficiently basic (e.g., N-Me-indole). (ii) When the amine component of the borocation is less nucleophilic (e.g., 2,6-lutidine), no additional base is required due to more facile amine dissociation from the boron center in the borylated arenium cation intermediate. Borenium cations do not borylate poorly activated arenes (e.g., toluene) even at high temperatures; instead, the key electrophile in this case involves the product from interaction of AlCl(3) with Y(2)BCl. When an extremely bulky amine is used, borylation again does not proceed via a borenium cation; instead, a number of mechanisms are feasible including via a boron electrophile generated by coordination of AlCl(3) to Y(2)BCl, or by initial (heteroarene)AlCl(3) adduct formation followed by deprotonation and transmetalation.

Bone selective protective effect of a novel bone-seeking estrogen on trabecular bone in ovariectomized rats.

The drawbacks of estrogen restrict the clinical use of hormone replacement therapy, and it would be most helpful to explore new estrogenic substances that could prevent bone loss and be free from any adverse effects. We synthesized a new compound named bone-seeking estrogen (SE2) by combining 17ß-estradiol (E2) with iminodiacetic acid through the Mannich reaction. E2 and SE2 were labeled with isotope (3)H, and the tissue distribution tests of E2-(3)H and SE2-(3)H were analyzed by the radioactivity. The specific nuclear binding of E2 and SE2 in osteoblasts was measured. SE2 exhibited significantly greater affinity for bone but lower affinity for ovary and uterus than did E2, and SE2 maintained a high affinity for the estrogen receptor alpha similar to that of E2. SE2 administration did not induce uterine hypertrophy. Body weight increase was significantly suppressed by treatment with E2 but not by SE2 after ovariectomy (OVX). SE2 decreased bone turnover as E2 after OVX detected by serum biochemical markers. Bone histology and micro-CT analysis revealed that SE2 administration, similar to E2, could improve bone mass and trabecular architecture after OVX. Biomechanical analyses showed that SE2 treatment effectively increased mechanical properties after OVX. The results suggested that SE2 was effective in preventing OVX-induced bone loss and exhibited few side effects on body weight and uterine hypertrophy, which was beneficial in reducing the adverse effects caused by E2. SE2 may be a better choice than E2 for the prevention of postmenopausal osteoporosis.

Pinene-derived iminodiacetic acid (PIDA): a powerful ligand for stereoselective synthesis and iterative cross-coupling of C(sp3) boronate building blocks.

Efficient access to chiral C(sp(3)) boronates in stereochemically pure form is critical for realizing the substantial potential of such building blocks in complex-molecule synthesis. We herein report that a pinene-derived iminodiacetic acid (PIDA) ligand enables the highly diastereoselective synthesis of a wide range of oxiranyl C(sp(3)) boronates from the corresponding olefins. These oxiranyl PIDA boronates, in turn, can be readily transformed into unprecedented stable α-boryl aldehydes via a novel 1,2-migration of the boronate group that proceeds with complete maintenance of stereochemical purity. B-Protected haloboronic acids containing dual sp(3)-hybridized C centers are readily accessible via this platform, and the herein demonstrated capacity for stereocontrolled iterative C(sp(3)) cross-coupling with this novel type of bifunctional reagent to access a medicinally important chiral small-molecule target in highly enantioenriched form represents a substantial advance for the building-block-based approach to synthesis.

Design of potential reverse transcriptase inhibitor containing Isatin nucleus using molecular modeling studies.

Two Dimensional (2D) and Three Dimensional (3D) Quantitative Structure-Activity Relationship (QSAR) studies were performed for correlating the chemical composition of Isatin analogues and their anti-HIV activity using Multiple Linear Regression (MLR) Analysis and k Nearest Neighbor Molecular Field Analysis (kNN MFA), respectively. New Chemical Entities (NCEs) were designed using results of QSAR studies. Binding affinities of designed NCEs were studied on Reverse Transcriptase enzyme using docking studies and their ADME properties were also predicted. Finally most promising compounds were selected from molecular modeling studies. Five compounds containing Isatin nucleus were synthesized and tested for their anti-HIV activity by performing Reverse Transcriptase Assay. Three compounds showed significant Reverse Transcriptase inhibiting activity compared to standard Navirapine. Structure-Activity Relationships were also discussed bases on obtained molecular modeling and experimental data.

Iminodiacetic Acid as a Novel Metal-Binding Pharmacophore for New Delhi Metallo-ß-lactamase Inhibitor Development.

The fungal natural product aspergillomarasmine A (AMA) has been identified as a noncompetitive inhibitor of New Delhi metallo-ß-lactamase-1 (NDM-1) that inhibits by removing ZnII from the active-site. The nonselective metal-chelating properties and difficult synthesis and derivatization of AMA have hindered the development of this scaffold into a potent and selective inhibitor of NDM-1. Iminodiacetic acid (IDA) has been identified as the metal-binding pharmacophore (MBP) core of AMA that can be leveraged for inhibitor development. Herein, we report the use of IDA for fragment-based drug discovery (FBDD) of NDM-1 inhibitors. IDA (IC50 =120 µM) was developed into inhibitor 23 f (IC50 =8.6 µM, Ki =2.6 µM), which formed a ternary complex with NDM-1, as evidenced by protein thermal-shift and native-state electrospray ionization mass spectrometry (ESI-MS) experiments. Combining mechanistic analysis with inhibitor derivatization, the use of IDA as an alternative AMA scaffold for NDM-1 inhibitor development is detailed.

Synthesis and bioevaluation of technetium-99 m / rhenium labeled phenylquinoxaline derivatives as Tau imaging probes.

Based on our previous research on the fluorinated phenylquinoxaline scaffold, in this study, different positions of N,N-dimethyl amino group, and alkyl linkers with various lengths were introduced into this scaffold to regulate their lipophilicity and binding affinity to Tau. Four novel 99mTc/Re complexes with diethyl iminodiacetate chelator were synthesized and evaluated as Tau imaging tracers in the brain of Alzheimer's disease. Their specific binding to neurofibrillary tangles was verified by in vitro fluorescence staining and further confirmed by the results of immunofluorescence staining on the same brain sections from AD patient and Tg-tau mice. From in vitro binding assay using recombinant Tau aggregates, complex 4.2 with 6-N(CH3)2 and longer carbon chain (n = 4) displayed the highest affinity (Kd = 59.95 nM). [99mTc]4.2 was achieved by the ligand exchange reaction between dicarboxylic precursor and [99mTc(CO)3(H2O)3]+ intermediate with radiochemical yield over 45%. Ex vivo biodistribution studies on normal ICR mice revealed that [99mTc]4.2 exhibited moderate initial brain uptake (0.61% ID/g) and more structure optimizations are still required to improve the blood-brain barrier permeability.

Asymmetric transfer hydrogenation of beta,gamma-alkynyl alpha-imino esters by a Brønsted acid.

Asymmetric synthesis of trans-alkenyl alpha-amino esters was realized by chiral phosphoric acid catalyzed transfer hydrogenation of beta,gamma-alkynyl alpha-imino esters. Utilizing Hantzsch esters as the hydrogen donor, both the alkyne and imine moieties of beta,gamma-alkynyl alpha-imino esters were reduced to afford trans-alkenyl alpha-amino esters with up to 96% ee.

Bifunctional monolithic affinity hydrogels for dual-protein delivery.

Multiple-protein delivery has been proven to be a critical consideration for promoting tissue regeneration. Many polymeric composite biomaterials have been designed and used for modulating dual-protein delivery to enhance tissue regeneration in vitro or in vivo. However, the fabrication conditions and low water contents within the portions of these composite matrices that determine protein release rates are not optimal for maintaining the stability of encapsulated macromolecular therapeutics. In this proof-of-concept work, we aim to resolve this deficiency by single-step fabrication of affinity hydrogels capable of independently delivering two or more proteins. Selective protein-binding sites were incorporated into poly(ethylene glycol) hydrogels via copolymerization with glycidyl methacrylate-iminodiacetic acid (GMIDA) ligands to modulate release of two model proteins, lysozyme and hexahistidine tagged green fluorescent protein (hisGFP), via two distinct matrix-binding mechanisms, namely electrostatic interaction and metal-ion chelation. Differing from composite matrices for dual-protein delivery, the results reported herein indicate that injectable monolithic affinity hydrogels are capable of rapidly encapsulating multiple therapeutic agents under mild physiological conditions and independently controlling their localized delivery. Most importantly, these affinity hydrogels retain high water permeabilities throughout the entire device, characteristics that are necessary for maintaining the stability and viability of encapsulated proteins and cells.

Stability of erythrocyte membrane and overall hemostasis potential - A biocompatibility study of mebrofenin and other iminodiacetic acid derivatives.

BACKGROUND: Intravenous injection seems to be the most convenient way of administering drugs and contrast agents, which makes components of the blood the first and usually unwanted target of their action. Binding of intravenously administered compounds to erythrocytes, blood platelets and vascular wall may have serious clinical implications. The aim of this study was to examine the influence of four iminodiacetic acid derivatives, potential ligands for gadolinium complexation, on the process of coagulation and fibrinolysis, activity of thrombin and hemolysis. METHODS: Kinetic parameters of coagulation and fibrinolysis process were determined during an optical CL-test based on measurement of transmittance alterations. Thrombin (0.5 IU/mL) and t-PA (240 ng/mL) were used to obtain a clotting and lysis curve. The activity of thrombin was determined with a chromogenic substrate S-2238. Hemolysis was examined spectrophotometrically and expressed as a percentage of released hemoglobin. RESULTS: Exposure to iminodiacetic acid derivatives resulted in a significant increase in the overall potential of clotting and lysis (CLAUC), as well as with the significant changes in the key parameters of these processes (thrombin time, initial plasma clotting velocity, clot stabilization time). Furthermore, iminodiacetic acid derivatives caused a significant decrease in the amidolytic activity of thrombin and enhanced hemolysis in a concentration-dependent manner. CONCLUSION: Despite their influence on the process of coagulation and fibrinolysis, amidolytic activity of thrombin and hemolysis, iminodiacetic acid derivatives should be generally considered safe as the significant effects were observed mostly at 4 µmol/mL, which is about 10-fold higher than the theoretical plasma concentration of these compounds.

History. Development of new radiopharmaceuticals based on N-substitution of iminodiacetic acid. By Michael D. Loberg, Malcolm Cooper, Elizabeth Harvey, Patrick Callery, and William Faith. 1976.

A new approach to radiopharmaceutical design is demonstrated, in which small chelating groups capable of binding gamma-emitting radiometals are attached to biologically active molecules, thus producing radiopharmaceuticals based on bifunctional drug and biochemical analogs. The chelating group iminodiacetic acid has been evaluated for this role by examining two N-substituted iminodiacetic acids: methyliminodiacetic acid (MIDA) and N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid (HIDA). Radiochemical and biologic studies showed that both agents were obtained in high radiochemical purity, were stable in vitro and in vivo, and possessed biologic distributions governed almost exclusively by the N-substituted group. These characteristics of 99mTc-labled N-substituted iminodiacetic acids, prepared using an "instant kit" method, provide the basis for a valuable new class of radiopharmaceuticals based on bifunctional drug and biochemical analogs.

The investigation of radiopharmaceutical components by fast atom bombardment mass spectrometry: the identification of Tc-HIDA and the epimers of Tc-CO2DADS.

The nature of two technetium-labeled radiopharmaceutical components has been established by means of fast-atom-bombardment mass spectrometry (FABMS) in combination with carrier-added (CA) and no-carrier-added (NCA) reversed-phase high-pressure liquid chromatography (HPLC). Negative-ion FABMS was used to determine that the epimers of Tc-CO2DADS are the oxo[N,N'-(1-carboxyethylene)-bis-(2-mercaptoacetimido)]technetate(V) ions; positive-ion FABMS showed that Tc-HIDA is bis[N-(2,6-dimethylphenyl-carbamoylmethyliminodiaceto]technetate(III).

Development of new radiopharmaceuticals based on N-substitution of iminodiacetic acid.

A new approach to radiopharmaceutical design is demonstrated, in which small chelating groups capable of binding gamma-emitting radiometals are attached to biologically active molecules, thus producing radiopharmaceuticals based on bifunctional drug and biochemical analogs. The chelating group iminodiacetic acid has been evaluated for this role by examining two N-substituted iminodiacetic acids: methyliminodiacetic acid (MIDA) and N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid (HIDA). Radiochemical and biologic studies showed that both agents were obtained in high radiochemical purity, were stable in vitro and in vivo, and possessed biologic distributions governed almost exclusively by the N-substituted group. These characteristics of 99mTc-labeled N-substituted iminodiacetic acids, prepared using an "instant kit" method, provide the basis for a valuable new class of radiopharmaceuticals based on bifunctional drug and biochemical analogs.

Evaluation of 99mTc-labeled iminodiacetic acid derivatives of substituted 2-aminopyrroles as hepatobiliary imaging agents in rats II.

The synthesis and biodistribution properties of 99mTc-labeled 5-substituted N-(3-cyano-4-methyl-2-pyrrylcarbamoylmethyl)iminodiacetic acids and a similar series of N1-methyl analogs are described. These compounds were compared with 99mTc-labeled N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid for hepatobiliary activity in the rat. The effects of structural modifications on biological activity are also reported.

Semisynthetic cephalosporins with alpha-oximino acid side chains. The preparation and coupling of 4-acylamino-alpha-oximinobenzeneacetic acids and 1,2-dihydro-6-methyl-alpha-oximino-2-oxo-3-pyridineacetic acid to 7-aminocephalosporanic acid.

A series of 4-acylamino-alpha-oximinobenzeneacetic acids, and 1,2-dihydro-6-methyl-alpha-oximino-2-oxo-3-pyridineacetic acid were prepared and coupled to 7-aminocephalosporanic acid and its 3'-(1-methyltetrazol-5-yl)thiolo analogue. Several coupling methods and oxime protecting groups were thoroughly examined. The best coupling procedure employed dimethylchloroformiminium chloride, and the tetrahydropyranyl (THP) group was selected for oxime protection. The cephalosporins prepared were tested and compared to cefuroxime and cefotaxime. The corresponding alpha-keto acids, and O-methyl oximes were also examined.

Preparation and biokinetic studies of 99mTc-p-butyl-IDA for hepatobiliary scintigraphy.

A freeze-dried powder of tin-p-butyl-IDA to be labelled with 99mTc for hepatobiliary scintigraphy has been developed. Gel chromatography column scanning has been applied for evaluating the labeling efficiency of the complex under different conditions. The results of organ distribution studies in mice and of clinical investigations in human beings showed the stability of the radiopharmaceutical. The preparative 99mTc-p-butyl-IDA concentrates moderately well in the bile with a rapid blood clearance into hepatocytes, very low excretion in the urine and slow clearance into the bile.

Technetium-99m complex of N-(2-pyridylmethyl)iminodiacetic acid as a new renal radiopharmaceutical.

A tetradentate chelating agent constituting of an iminodiacetic acid group and a nitrogen atom of pyridine, N-(2-pyridylmethyl)iminodiacetic acid (PMIDA), was coordinated with 99mTc and evaluated as a renal functional agent. The complex of PMIDA with 99mTc was prepared by using a stannous chloride solution as a reducing agent. The chelating efficiency was analyzed by thin layer chromatography and electrophoresis. Chelation with 99mTc resulted in a single radiochemical product. Biological studies were performed in mice and rats. 99mTc-PMIDA was removed from the circulation solely by the kidneys. Clearance of 99mTc-PMIDA from the blood and the kidneys was as rapid as that of 99mTc-diethylenetriaminepentaacetic acid. The rate of blood clearance was unaffected by the administration of probenecid (a test for tubular secretion by the weak-acid mechanism), so that the glomerular filtration rate could be estimated by measuring its clearance from the blood. The results in animals with myohemoglobinuric acute renal failure suggested that 99mTc-PMIDA might be a useful renal function radiopharmaceutical.

Preparation and in-vivo evaluation of 99mTc-IOTIDA for cholescintigraphy.

The synthesis, radiolabeling and in vivo evaluation of 99mTc-IOIDA(3-iodo 2,4,6-trimethylpheyl carbamoylmethyl iminodiacetic acid) for the assessment of hepatocytic function and the functional status of the cystic duct and the gallbladder are described. For a scintigraphic imaging comparison, three different 99mTc-IDA derivatives, 99mTc-DISIDA, 99mTc-mebrofenin and 99mTc-IOTIDA, were prepared and evaluated for their in vivo pharmacokinetic behavior through animal studies. Serial static image scans of rabbits injected with 99mTc-IOTIDA revealed that none of the tissues except the hepatobiliary system showed radioactivity concentrations. A scintigraphic study in a healthy volunteer showed that most of the administrated radioactivity accumulated in the liver and was rapidly excreted through the hepatobiliary system, visualizing the gallbladder within 15 min. In conclusion, 99mTc-IOTIDA is a potential hepatobiliary imaging agent for the evaluation of the functional status of hepatocytes and the patency of the biliary duct.

Synthesis, spectroscopy, and binding constants of ketocatechol-containing iminodiacetic acid and its Fe(III), Cu(II), and Zn(II) complexes and reaction of Cu(II) complex with H2O2 in aqueous solution.

A new neuromelanin-like ketocatechol-containing iminodiacetic acid ligand, (N-(3,4-dihydroxyl)phenacylimino)diacetic acid (H4L), which is also quite similar to compounds found in insect cuticle, has been synthesized and characterized. The X-ray crystal structure of H4L has been successfully determined. Proton binding and coordination with Fe(III), Cu(II), and Zn(II) have been studied by potentiometric titrations and UV-vis spectrophotometry in aqueous solution. UV spectra of H4L in the absence and presence of different metal ions indicate complexes formed with the catechol moiety of H4L in aqueous solution. Visible spectra and NMR reveal that H4L with Fe(III), Cu(II), and Zn(II) can all give stable mono-(ML) and dinuclear complexes [M(ML)]. Fe(III) can also form {Fe(FeL)2} and {Fe(FeL)3} species with sufficient base. The process is accompanied by a drastic color change from light blue to deep-blue to wine-red. The Fe(III)-Cu(II) heteronuclear complex also exists in aqueous solution whose spectra are similar to the homonuclear Fe(III) complex. However, the spectra of {Fe(CuL)} shifted to a longer wavelength and {Fe(CuL)2} and {Fe(CuL)3} shifted to a shorter wavelength. Keto-enol tautomerism was observed in weak basic aqueous solution as indicated by (1)H NMR spectra. The reaction products of Cu(II) complex with H2O2 depend on the H2O2 concentration and pH value. Low concentrations of H2O2 oxidize H4L to a series of semiquinone and quinone compounds with absorption maxima at 314-400 nm, while a high concentration of H2O2 oxidizes H4L to colorless muconic acid derivatives. NaIO4 gives different oxidase products, but no 2,4,5-trihydroxyphenylalanine quinone (TPQ)-like hydroxyquinone can be found.