Combinatorial solid phase synthesis of multiply substituted 1,4-benzodiazepines and affinity studies on the CCK2 receptor (Part 1)

One hundred sixty-eight multiply substituted 1,4-benzodiazepines have been prepared by a five-step solid-phase combinatorial approach using syn-phase crowns as a solid support and a hydroxymethyl-phenoxy-acetamido linkage (Wang linker). The substituents of the 1,4-benzodiazepine scaffold have been varied in the -3, -5, -7, and 8-positions and the combinatorial library was evaluated in a cholecystokinin (CCK) radioligand binding assay. 3-Alkylated 1,4-benzodiazepines with selectivity towards the CCK-B (CCK2) receptor have been optimized on the lipophilic side chain, the ketone moiety, and the stereochemistry at the 3-position. Various novel 3-alkylated compounds were synthesized and [S]3-propyl-5-phenyl-1,4-benzodiazepin-2-one, [S]NV-A, has shown a CCK-B selective binding at about 180 nM. Fifty-eight compounds of this combinatorial library were purified by preparative TLC and 25 compounds were isolated and fully characterized by TLC, IR, APCI-MS, and 1H/13C-NMR spectroscopy.

Synthesis and evaluation of N1-substituted-3-propyl-1,4-benzodiazepine-2-ones as cholecystokinin (CCK2) receptor ligands

A novel synthetic approach towards N1-alkylated 3-propyl-1,4-benzodiazepines was developed in five synthetic steps from 2-amino-4-chlorobenzophenone, in which the N-oxide 4 served as a key intermediate. The structure-activity relationship optimization of this 3-prophyl-1,4-benzodiazepine template was carried out on the N1-position by selective alkylation reactions and resulted in a ligand with an improved affinity on the cholecystokinin (CCK2) receptor. The N-allyl-3-propyl-benzodiazepine 6d displayed an affinity towards the CCK2 (CCK-B) receptor of 170 nM in a radiolabelled receptor-binding assay. The anxiolytic activity of this allyl-3-propyl-1,4-benzodiazepine 6d was subsequently determined in in-vivo psychotropic assays. This novel ligand had ED50 values of 4.7 and 5.2 mg kg-1 in the black and white box test and the x-maze, respectively, and no significant sedation/muscle relaxation was observed.

Hypervalent iodine in synthesis 92. A facile synthesis of 3-substituted-5,6-dihydroimidazo[2,1-b]thiazoles by cyclocondensation of alkynyl(phenyl)iodonium salts and imidazolidine-2-thione

A simple method for the synthesis of 3-substituted 5,6-dihydroimidazo[2,1-b]thiazoles is achieved by cyclocondensation of alkynyl(phenyl)iodonium salts with imidazolidine-2-thione.

Hypervalent Iodine in Synthesis. 94. A Facile Synthesis of 2-Substituted-imidazo[1,2-a]pyridines by Cyclocondensation of Alkynyl(phenyl) iodonium Salts and 2-Aminopyridine

A facile method for the synthesis of 2-substituted-imidazo[1,2-a]pyridines is achieved by cyclocondensation of alkynyl(phenyl)iodonium salts with 2-aminopyridine.

Hypervalent iodine in synthesis 93. A facile synthesis of 2-substituted imidazo[1,2-a]pyrimidines by cyclocondensation of alkynyl(phenyl)iodonium salts and 2-aminopyrimidine

Simple stirring of a mixture of the alkynyl(phenyl)iodonium salts 1 with 2-aminopyrimidine 2 in chloroform under reflux for two hours in the presence of K2CO3 gave, after workup, the 2-substituted imidazo[1,2-]pyrimidines 3 in moderate to good yields. A possible mechanism for the formation of 3 involves the intramolecular cyclization of the intermediate alkylidenecarbene 6.

Combinatorial approach to multi-substituted 1,4-Benzodiazepines as novel non-peptide CCK-antagonists

For the drug discovery process, a library of 168 multisubstituted 1,4-benzodiazepines were prepared by a 5-step solid phase combinatorial approach. Substituents were varied in the 3,5, 7 and 8-position on the benzodiazepine scaffold. The combinatorial library was evaluated in a CCK radiolabelled binding assay and CCKA (alimentary) and CCKB (brain) selective lead structures were discovered. The template of CCKA selective 1,4-benzodiazepin-2-ones bearing the tryptophan moiety was chemically modified by selective alkylation and acylation reactions. These studies provided a series of Asperlicin naturally analogues. The fully optimised Asperlicin related compound possessed a similar CCKA activity as the natural occuring compound. 3-Alkylated 1,4-benzodiazepines with selectivity towards the CCKB receptor subtype were optimised on A) the lipophilic side chain and B) the 2-aminophenyl-ketone moiety, together with some stereochemical changes. A C3 unit in the 3-position of 1,4-benzodiazepines possessed a CCKB activity within the nanomolar range. Further SAR optimisation on the N1-position by selective alkylation resulted in an improved CCKB binding with potentially decreased activity on the GABAA/benzodiazepine receptor complex. The in vivo studies revealed two N1-alkylated compounds containing unsaturated alkyl groups with anxiolytic properties. Alternative chemical approaches have been developed, including a route that is suitable for scale up of the desired target molecule in order to provide sufficient quantities for further in vivo evaluation.

Chemical synthesis of DNA and RNA containing thio-substituted bases and their post-synthetic modifications

Modified oligonucleotides containing sulphur group have been useful tools for studies of carcinogenesis, protein or nucleic acid structures and functions, protein-nucleic acid interactions, and for antisense modulation of gene expression. One successful example has been the synthesis and study of oligodeoxynucleotides containing 6-thio-2'-deoxyguanine. 6-Thio-2-deoxyguanosine was first discovered as metabolic compound of 6- mercaptopurine (6-MP). Later, it was applied as drug to cure leukaemia. During the research of its toxicity, a method was developed to use the sulphur group as a versatile position for post-synthetic modification. The advantage of application of post-synthetic modification lies in its convenience. Synthesis of oligomers with normal sequences has become routine work in most laboratories. However, design and synthesis of a proper phosphoramidite monomer for a new modified nucleoside are always difficult tasks even for a skilful chemist. Thus an alternative method (post-synthetic method) has been invented to overcome the difficulties. This was achieved by incorporation of versatile nucleotides into oligomers which contain a leaving group, that is sufficiently stable to withstand the conditions of synthesis but can be substituted by nucleophiles after synthesis, to produce, a series of oligomers each containing a different modified base. In the current project, a phosphoramidite monomer with 6-thioguanine has been successfully synthesised and incorporated into RNA. A deprotection procedure, which is specific for RNA was designed for oligomers containing 6-thioguanosine. The results were validated by various methods (UV, HPLC, enzymatic digestion). Pioneer work in utilization of the versatile sulphur group for post-synthetic modification was also tested. Post-synthetic modification was also carried out on DNA with 6- deoxythioguanosine. Electrophilic reagents with various functional groups (alphatic, aromatic, fluorescent) and bi-functional groups have been attached with the oligomers.

Study of neutral Fe(III) complexes of pyridoxal-N-substituted thiosemicarbazone with desolvation induced spin-state transformation above room temperature

The preparation and characterization of two new neutral ferric complexes with desolvation-induced discontinuous spin-state transformation above room temperature are reported. The compounds, Fe(Hthpy)(thpy).CH3OH.3H2O (1) and Fe(Hmthpy)(mthpy).2H2O (2), are low-spin (LS) at room temperature and below, whereas their nonsolvated forms are high-spin (HS), exhibiting zero-field splitting. In these complexes, Hthpy, Hmthpy, and thpy, mthpy are the deprotonated forms of pyridoxal thiosemicarbazone and pyridoxal methylthiosemicarbazone, respectively; each is an O,N,S-tridentate ligand. The molecular structures have been determined at 100(1) K using single-crystal X-ray diffraction techniques and resulted in a triclinic system (space group P1) and monoclinic unit cell (space group P21/c) for 1 and 2, respectively. Structures were refined to the final error indices, where RF = 0.0560 for 1 and RF = 0.0522 for 2. The chemical inequivalence of the ligands was clearly established, for the "extra" hydrogen atom on the monodeprotonated ligands (Hthpy, Hmthpy) was found to be bound to the nitrogen of the pyridine ring. The ligands are all of the thiol form; the doubly deprotonated chelates (thpy, mthpy) have C-S bond lengths slightly longer than those of the singly deprotonated forms. There is a three-dimensional network of hydrogen bonds in both compounds. The discontinuous spin-state transformation is accompanied with liberation of solvate molecules. This is evidenced also from DSC analysis. Heat capacity data for the LS and HS phases are tabulated at selected temperatures, the values of the enthalpy and entropy changes connected with the change of spin state were reckoned at DeltaH = 12.5 0.3 kJ mol-1 and DeltaS = 33.3 0.8 J mol-1 K-1, respectively, for 1 and DeltaH = 6.5 0.3 kJ mol-1 and DeltaS = 17.6 0.8 J mol-1 K-1, respectively, for 2

Tuning of the charge in octahedral ferric complexes based on pyridoxal-N substituted thiosemicarbazone ligands

Four novel mononuclear coordination compounds namely: [Fe(Hthpy)2](SO4)1/2·3.5H2O 1, [Fe(Hthpy)2]NO3·3H2O 2, [Fe(H2mthpy)2](CH3C6H4SO3)3·CH3CH2OH 3 and [Fe(Hethpy)(ethpy)]·8H2O 4, (H2thpy = pyridoxalthiosemicarbazone, H2mthpy = pyridoxal-4-methylthiosemicarbazone, H2ethpy = pyridoxal-4-ethylthiosemicarbazone), were synthesized in the absence or presence of organic base, Et3N and NH3. Compounds 1 and 2 are monocationic, and were prepared using the singly deprotonated form of pyridoxalthiosemicarbazone. Both compounds crystallise in the monoclinic system, C2/c and P21/c space group for 1 and 2, respectively. Complex 3 is tricationic, it is formed with neutral bis(ligand) complex and possesses an interesting 3D channel architecture, the unit cell is triclinic, P1 space group. For complex 4, the pH value plays an important role during its synthesis; 4 is neutral and crystallises with two inequivalent forms of the ligand: the singly and the doubly deprotonated chelate of H2ethpy, the unit cell is monoclinic, C2/c space group. Notably, in 1 and 4, there is an attractive infinite three dimensional hydrogen bonding network in the crystal lattice. Magnetic measurements of 1 and 4 revealed that a rather steep spin transition from the low spin to high spin Fe(III) states occurs above 300 K in the first heating step. This transition is accompanied by the elimination of solvate molecules and thus, stabilizes the high spin form due to the breaking of hydrogen bonding networks; compared to 2 and 3, which keep their low spin state up to 400 K.

Preparation of 9-substituted pyridine-stretched adenines and hypoxanthines

9-Methylsulfanyl pyridine-stretched adenine and hypoxanthine derivatives have been prepared via regioselective reaction of a 5-aminoimidazole with 2-(bis-methylsulfanylmethylene)malononitrile [(NC)C=C(SMe) ]. The 9-methylsulfanyl substituent can be replaced by sequential oxidation and substitution by nucleophiles including amines.

Some substituted piperidines of potential biological interest

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Novel anti-bacterials against MRSA:Synthesis of focussed combinatorial libraries of tri-substituted 2(5H)-furanones

Mucobromic and mucochloric acid were used as building blocks for the construction of a chemical combinatorial library of 3,4,5-trisubstituted 2(5H)-furanones. With these 2 butenolide building blocks, and eight alcohols a sublibrary of 16 dihalogenated 5-alkoxy-2(5H)-furanones was prepared. This sublibrary of 5-alkoxylated furanones was reacted with 16 amines generating a full size focussed combinatorial library of 256 individual compounds. This three dimensional combinatorial library of 3-halogen-4-amino-5-alkoxy-2(5H)-furanones was prepared around the benzimidazolyl furanone lead structure by applying a solution phase combinatorial chemistry concept. Typical representatives of the library were purified and fully characterized and one x-ray structures was recorded, additionally. The 3-bromo-4-benzimizazolyl-5-methoxy-2(5H)furanone, Br-A-l, showed an MIC of 8 μg/ml against the multiresistant Staphylococcus aureus ( MRSA). © 2006 Bentham Science Publishers Ltd.

Antibacterial activity of 3-substituted pyrrole-2,5-diones against Pseudomonas aeruginosa

3-Substituted pyrrole-2,5-diones were synthesised from mucohalogen acids and the antibacterial activity was subsequently determined in biological assays. The minimum inhibitory concentration and the minimum bactericidal concentration of 2a were determined for a wide range of microorganisms in the low micromolar range. Protein identification using SDS-PAGE and LC/MS/MS demonstrated a partly degradation of OprF-related proteins giving an insight into the underlying mechanism of these novel antibacterial agents. © 2007 Bentham Science Publishers Ltd.