[Synthesis and bioactivity of N- [4- ( benzimidazole-2-thio) phenyl] -N'-alkyl guanidine derivatives]

In order to get some novel compounds with potent iNOS inhibitory activity, 12 target compounds of N-[ 4-( benzimidazole-2-thio) phenyl ] -N'-alkyl guanidine derivatives ( I1- I12 ) were synthesized from 1-benzoyl-3-[ 4-( benzimidazole-2-thio) phenyl] thioureas (4) by hydrolysis with 2. 0 mol x L(-1) sodium hydroxide solution containing tetrahydrofuran to form the corresponding N-[ 4-(benzimidazole-2-thio) phenyl] thioureas (5) which was S-ethylated with ethyl iodide, followed by amination with primary amines or secondary amines. The intermediate 4 was synthesized from 2-mercaptobenzimidazole (1) by reaction with 1-chloro-4-nitrobenzene to form 2-( 4-nitrophenylthio) benzimidazole (2) which was reduced by iron powder and hydrochloric acid, followed by reaction with benzoyl isothiocyanate. The structures of compounds I1 - I12 were confirmed by IR, MS,1H NMR and elemental analysis. The results of preliminary pharmacological test showed that the activities of three compounds (I 1, I8 and I10) were stronger than aminoguanidine, especially for compound I1.

Marine natural products: synthetic aspects

An overview of marine natural products synthesis during 2005 is provided. In a similar vein to earlier installments in this series, the emphasis is on total syntheses of molecules of contemporary interest, new total syntheses, and syntheses that have resulted in structure confirmation or stereochemical assignments.

Synthesis and characterization of guanidinylated poly(propylene imine) dendrimers as gene transfection agents

Fourth generation poly(propylene imine) dendrimer has been completely or partially functionalized with guanidinium groups. In the second case, the remaining toxic primary amino groups of the dendrimers were reacted with propylene oxide affording the corresponding hydroxylated derivatives. Five derivatives have been prepared bearing 0, 6, 12, 24 or 32 guanidinium groups. These guanidinylated dendrimers were interacted with plasmid DNA affording the corresponding dendriplexes. The complexes were physicochemically characterized by dynamic light scattering, zeta-potential measurements and AFM, while the extent of complexation was evaluated by agarose gel electrophoresis. Furthermore, their transfection efficiency was assessed employing HEK 293 and COS-7 cell lines, while the serum effect was studied in HEK 293 cells. It was found that complete replacement of primary amino groups with the hydroxylated moieties resulted in complete loss of transfection efficiency. On the contrary, guanidinylation of the parent dendrimer resulted to significant enhancement of its transfection efficiency, this enhancement being dependent on the number of guanidinium groups per dendrimer, the cell line used and the presence or absence of FBS. The fully guanidinylated dendrimer exhibited the best transfection efficiency under all the conditions studied. This efficiency has been attributed to the enhanced penetrating ability of the guanidinylated dendrimers due to the accumulation of the guanidinium group at the dendrimeric surface. It was also found that the derivative with 12 guanidinium groups exhibited the lowest toxicity. The reduction of toxicity was apparently attributed to the decrease of the external primary amino groups coupled with the presence of hydroxylated moieties located at the dendrimeric surface. The functionalization strategy employed leads to dendrimeric derivatives that combine satisfactory transfection efficiency and cytotoxicity.

Total synthesis of (+)-batzelladine A and (-)-batzelladine D, and identification of their target protein

Asymmetric total synthesis of batzelladine A (1) and batzelladine D (2) has been achieved. Our synthesis of batzelladines features 1) stereoselective construction of the cyclic guanidine system by means of successive 1,3-dipolar cycloaddition reaction and subsequent cyclization, 2) direct esterification of the bicyclic carboxylic acid 35 with the guanidine alcohol 8 or 59 to construct the whole carbon skeleton of batzelladines, and 3) one-step formation of the alpha,beta-unsaturated aldehyde 53 from the primary alcohol 47 with tetra-n-propylammoniumperruthenate (TPAP), providing an efficient route to the left-hand bicyclic guanidine alcohol of batzelladine A (1). With the synthetic compounds 1 and 2 in hand, their target protein was examined by using immobilized CD4 and gp120 affinity gels. The results indicated that batzelladines A (1) and D (2) bind specifically to CD4.

Exploration of potential prodrugs of RWJ-445167, an oxyguanidine-based dual inhibitor of thrombin and factor Xa

Compound 2 (RWJ-445167; 3DP-10017), a dual inhibitor of thrombin and factor Xa, was advanced into human clinical studies. However, its oral bioavailability in humans proved to be below acceptable limits. To address this issue, we explored a prodrug approach involving numerous guanidine derivatives. Prodrug candidates of classes A (carbamate derivatives), B (imidate derivatives), and C (alkyl and acyl derivatives), compounds 3-6, were synthesized and evaluated for anticoagulant activity at 2 h after oral administration to rats. In comparison to the parent drug (2), little worthwhile improvement was observed for the prodrug candidates.

Discovery ofS-(2-Guanidylethyl)-isothiourea (VUF 8430) as a Potent Nonimidazole Histamine H4Receptor Agonist

During an in-house database screen, we identified S-(2-guanidylethyl)-isothiourea as a high affinity agonist for the histamine H4 receptor, with a 33-fold selectivity over the histamine H3 receptor and negligible affinity for the other histamine receptor subtypes. This nonimidazole ligand is introduced as a useful and complementary pharmacological tool that enables further unraveling of the physiological roles of the H4 receptor.

Asymmetric Total Synthesis of (+)-K01-0509 B: Determination of Absolute Configuration

K01-0509 B is a novel natural product which contains a carbamoylated cyclic guanidine. Our asymmetric total synthesis features a Sharpless asymmetric epoxidation and a stereocontrolled construction of the cyclic guanidine via an asymmetric nitroaldol reaction, followed by intramolecular SN2 cyclization. These reactions allowed the cyclic guanidine and the adjacent hydroxy group to be assembled, facilitating the asymmetric total synthesis and determination of the absolute stereochemistry of K01-0509 B. [reaction: see text].

Total synthesis of (+)-batzelladine A and (-)-batzelladine D via [4 + 2]-annulation of vinyl carbodiimides with N-alkyl imines

A diastereoselective [4 + 2]-annulation of vinyl carbodiimides with chiral N-alkyl imines has been developed to access the stereochemically rich polycyclic guanidine cores of the batzelladine alkaloids. Application of this strategy, together with additional key steps such as long-range directed hydrogenation and diastereoselective intramolecular iodo-amination, led to highly convergent total syntheses of (-)-batzelladine D and (+)-batzelladine A with excellent stereocontrol.

Syntheses of triazole-modified zanamivir analogues via click chemistry and anti-AIV activities

Sixteen novel 4-triazole-modified zanamivir (1) analogues were synthesized using the click reactions, and their inhibitory activities against avian influenza virus (AIV, H5N1) were determined. Compound 3b exerts promising inhibitory activity with EC(50) of 6.4 microM, which is very close to that of zanamivir (EC(50) = 2.8 microM). Molecular modeling provided the information about the binding model between inhibitors and neuraminidase, which are in good agreement with inhibitory activities.

Acylguanidines as Small-Molecule β-Secretase Inhibitors

BACE1 is an aspartyl protease responsible for cleaving amyloid precursor protein to liberate Abeta, which aggregates leading to plaque deposits implicated in Alzheimer's disease. We have identified small-molecule acylguanidine inhibitors of BACE1. Crystallographic studies show that these compounds form unique hydrogen-bonding interactions with the catalytic site aspartic acids and stabilize the protein in a flap-open conformation. Structure-based optimization led to the identification of potent analogs, such as 10d (BACE1 IC(50) = 110 nM).

Design, synthesis, and structure-activity relationships of novel 2-substituted pyrazinoylguanidine epithelial sodium channel blockers: drugs for cystic fibrosis and chronic bronchitis

Amiloride (1), the prototypical epithelial sodium channel (ENaC) blocker, has been administered with limited success as aerosol therapy for improving pulmonary function in patients with the genetic disorder cystic fibrosis. This study was conducted to synthesize and identify more potent, less reversible ENaC blockers, targeted for aerosol therapy and possessing minimal systemic renal activity. A series of novel 2-substituted acylguanidine analogues of amiloride were synthesized and evaluated for potency and reversibility on bronchial ENaC. All compounds tested were more potent and less reversible at blocking sodium-dependent short-circuit current than amiloride. Compounds 30-34 showed the greatest potency on ENaC with IC(50) values below 10 nM. A regioselective difference in potency was found (compounds 30, 39, and 40), whereas no stereospecific (compounds 33, 34) difference in potency on ENaC was displayed. Lead compound 32 was 102-fold more potent and 5-fold less reversible than amiloride and displayed the lowest IC(50) value ever reported for an ENaC blocker.

Design and synthesis of potent and selective 1,3,4-trisubstituted-2-oxopiperazine based melanocortin-4 receptor agonists

The design and synthesis of a series of potent 1,3,4-trisubstituted-2-oxopiperazine based MC4 agonists are described. The tripeptidomimetic analogs (12a,b and 23) and the dipeptidomimetic 27 displayed single-nanomolar binding affinity and agonist potency for MC4R and excellent selectivity for MC4R relative to MC1R.

Solid-phase synthesis of positively charged deoxynucleic guanidine (DNG) oligonucleotide incorporating 7-deazaguanine bases

DNG nucleotides represent a positively charged DNA analog in which the negatively charged phosphodiester linkages of DNA are replaced by positively charged guanidinium linkages. We report herein the synthesis of 3'-end, middle, and 5'-end monomers required for the synthesis of a DNG sequence in which the natural guanine base is replaced by 7-deazaguanine (c(7)G). 7-Deazaguanine nucleobase was chosen because of their unique glycoside bond stability and their ability to prevent G-quartet formation. A facile and high yield two-step synthesis of xylo-7-deazaguanine 7, a key intermediate for introducing 3'-amino functionality, is carried out under Mitsunobu conditions. Subsequently, the 3'-Fmoc-protected thiourea monomers 13 and 19 were prepared from 7 via their corresponding 3'-amino-7-deazaguanines 11 and 18, respectively. The smooth coupling of these thiourea monomers with monomethoxytrityl (MMTr)-protected 3'-end monomer 25, prepared from 5, occurred on solid phase in 3'-->5' direction. The resultant trimeric HO-c(7)Ggc(7)Ggc(7)G-OH (1) has been designed to be included into DNA using standard DNA synthesis technology. The combination of C-c(7)G base pairing and electrostatic association of phosphodiester and guanidinium backbone allows the small synthesized DNG trimer 1 to form 1:1 complex with DNA-C pentamer.

Synthesis and pharmacological characterization of novel fluorescent histamine H2-receptor ligands derived from aminopotentidine

In an effort to develop a non-radioactive alternative to the [3H]tiotidine and [125I]iodoaminopotentidine binding assays for the histamine H2-receptor (H2R), primary amines related to aminopotentidine were prepared and coupled with the succinimidyl esters of the bulky fluorescent dyes S0536 and BODIPY 650/665-X. The primary amines exhibited different degrees of antagonistic potency at the human and guinea pig H2R. Surprisingly, one compound (5) coupled to the cyanine dye S0536 acted as potent partial agonist/antagonist at the H2R (KB approximately 50 nM; EC50 approximately 100-150 nM). Compounds coupled to the BODIPY dye exhibited moderately high H2R-affinity, too. Thus, the H2R accommodates bulky fluorophores, probably through interaction with extracellular receptor domains. The compounds presented herein provide a starting point for the optimization of fluorescent H2R ligands with respect to affinity and fluorescence as valuable tools to analyze the molecular mechanisms of H2R activation.

DNA binding affinity of bisguanidine and bis(2-aminoimidazoline) derivatives with in vivo antitrypanosomal activity

A new antitrypanosomal hit compound that cures an acute (STIB 900) mouse model of Trypanosoma brucei rhodesiense trypanosomiasis is described. This bis(2-aminoimidazolinium) dicationic compound proved to be an excellent DNA minor groove binder, suggesting a possible mechanism for its trypanocidal activity. From these studies, the 4,4'-diaminodiphenylamine skeleton emerged as a good scaffold for antitrypanosomal drugs.

Inhibition of trypsin and urokinase by Cbz-amino(4-guanidinophenyl)methanephosphonate aromatic ester derivatives: The influence of the ester group on their biological activity

The urokinase plasminogen activator is a trypsin-like serine protease, important in tumor development. Here, we report the synthesis and biochemical evaluation of selective and potent diaryl esters of phosphonic-type inhibitors for urokinase. We have found that the substituted phenyl ester ring has a strong influence on the inhibitory activity of these compounds. This led to the most potent phosphonic inhibitor for uPA synthesized to date.

Functional organisation and gain of activity: The case of the antibacterial tetra-para-guanidinoethyl-calix[4]arene

The antibacterial activities of the para-guanidinoethylphenol and of its cyclic tetramer, the tetra-para-guanidinoethyl-calix[4]arene, have been evaluated on reference gram-positive and gram-negative bacteria. Antibiotic disk diffusion assays completed by micromethod technique were employed to determine if a synergistic effect could be expected from the spatial organisation of the monomer into its cyclic tetrameric analogue. Disk diffusion assays and microdilution experiments revealed better properties for the calixarene species, with a real and important gain of activity with regards to the monomer.

Synthesis and Pharmacological Evaluation of Novel Nitrobenzenic Thromboxane Modulators as Antiplatelet Agents Acting on Both the Alpha and Beta Isoforms of the Human Thromboxane Receptor

Thromboxane A(2) (TXA(2)) is an arachidonic acid metabolite involved in pathologies such as stroke, myocardial infarction, and atherosclerosis. Consequently, the design of TXA(2) receptor (TP) antagonists remains of great interest in cardiovascular medicine. The actions of TXA(2) are mediated by its specific G-protein coupled receptor of which two alternative spliced isoforms, TPalpha and TPbeta, have been described in humans. In this study, we report the synthesis of a series of original N-alkyl-N'-[2-(cycloalkyl, alkylaryl)-5-nitrobenzenesulfonyl]urea and N-alkyl-N'-[2-(alkylaryl)-5-nitrobenzenesulfonyl]-N' '-cyanoguanidines and outline their pharmacological evaluation using the individual TPalpha and TPbeta isoforms. Among compounds analyzed, several of them exhibited greater affinity and/or functional activity for either TPalpha or TPbeta. The most promising molecules were also found to be antiplatelet agents. From the present results, structural features involved in isoform selectivity can be proposed, and thereby several lead compounds have been identified for the further development of selective TP isoform antagonists.

An Efficient Direct Amination of Cyclic Amides and Cyclic Ureas

[reaction: see text] An efficient one-step amination of cyclic amides and ureas has been developed. Treatment of cyclic amides and cyclic ureas with BOP in the presence of DBU in various solvents led to the formation of cyclic amidines and cyclic guanidines in good to excellent yields. Concise syntheses of biologically intriguing kinetin and potent kinase inhibitor olomoucin were thus achieved in just one and two steps, respectively.

A Bis-guanidine-Based Multisignaling Sensor Molecule That Displays Redox-Ratiometric Behavior or Fluorescence Enhancement in the Presence of Anions and Cations

[structure: see text]The guanidine bridge in the new structural motif [3,3]ferrocenophane acts as a dual binding site for anions and metal ions. Sensing of anions (Cl(-), F(-), NO(3)(-), HSO(4)(-), and H(2)PO(4)(-)) takes place by redox-ratiometric measurements, whereas metal ion (Zn(2+), Ni(2+), and Cd(2+)) recognition is achieved by fluorescence measurements.

Novel alkylpolyaminoguanidines and alkylpolyaminobiguanides with potent antitrypanosomal activity

A series of polyaminoguanidines and polyaminobiguanides were synthesized and evaluated as potential antitrypanosomal agents. These analogues inhibit trypanothione reductase (TR) with IC50 values as low as 0.95 microM, but do not inhibit the closely related human enzyme glutathione reductase (GR). The most effective analogues, 7a, 7b and 8d, inhibited parasitic growth in vitro with IC50 values of 0.18, 0.09 and 0.18 microM, respectively. These agents represent a promising new class of potential antitrypanosomal agents.

Synthesis and cytotoxic evaluation of new derivatives of the marine alkaloid variolin B

The marine alkaloid variolin B 2 and eight synthetic derivatives with different substituents at positions C-5 and C-7 have been tested in a panel of sixteen human tumor cell lines to evaluate their cytotoxic potential.

Marine natural products: synthetic aspects

An overview of marine natural products synthesis during 2004 is provided. As with the previous installment of this series, the emphasis is on total syntheses of molecules of contemporary interest, new total syntheses, and syntheses that have resulted in structure confirmation or stereochemical assignments.

Solid-Phase Synthesis in the Twenty-First Century

Solid-phase synthesis is a powerful tool for achieving high-throughput chemistry. This review discusses recent diverse examples from my group: the solid-phase synthesis of unsymmetrical guanidines, polymer-supported versions of cyclooctadiene and 9-BBN, a triflate-like linker, the synthesis of tetrahydro-beta-carbolines by the acyliminium Pictet-Spengler reaction, and a total synthesis of the antimycobacterial cyclic depsipeptide natural product kahalalide A.