Dušan Sladić

Reactivity and biological activity of the marine sesquiterpene hydroquinone avarol and related compounds from sponges of the order Dictyoceratida.

A review of results of bioactivity and reactivity examinations of marine sesquiterpene (hydro)quinones is presented. The article is focused mostly on friedo- rearranged drimane structural types, isolated from sponges of the order Dictyoceratida. Examples of structural correlations are outlined. Available results on the mechanism of redox processes and examinations of chemo- and regioselectivity in addition reactions are presented and, where possible, analyzed in relation to established bioactivities. Most of the bioactivity examinations are concerned with antitumor activities and the mechanism thereof, such as DNA damage, arylation of nucleophiles, tubulin assembly inhibition, protein kinase inhibition, inhibition of the arachidonic cascade, etc. Perspectives on marine drug development are discussed with respect to biotechnological methods and synthesis. Examples of the recognition of validated core structures and synthesis of structurally simplified compounds retaining modes of activity are analyzed.

A novel lectin from the sponge Haliclona cratera: isolation, characterization and biological activity

A lectin from the Adriatic sponge Haliclona cratera was purified by ion-exchange and gel chromatography. The molecular mass of the lectin is approximately 29 kDa. Purified lectin is rich in hydrophobic and basic amino acids and has an isoelectric point at pH 8.6. H. cratera lectin is relatively heat- and pH-stable. It agglutinates native and trypsinized, papainized and neuraminidase-treated human A, B, O, AB and sheep erythrocytes, and the hemagglutinating activity is independent of Ca(2+), Mn(2+) and Mg(2+) ions; D-galactose and N-acetyl-D-galactosamine are found to be moderate inhibitors of the activity. H. cratera lectin displays cytotoxic effect on HeLa and FemX cells and weak mitogenic effect on human T-lymphocytes pretreated with phytohemagglutinin (PHA).

Synthesis and characterization of new Pt(II) and Pd(II) complexes with 2-quinolinecarboxaldehyde selenosemicarbazone: Cytotoxic activity evaluation of Cd(II), Zn(II), Ni(II), Pt(II) and Pd(II) complexes with heteroaromatic selenosemicarbazones

New complexes of Pt(II) and Pd(II) with 2-quinolinecarboxaldehyde selenosemicarbazone were synthesized and characterized by elemental analysis, NMR and IR spectroscopy and molar conductivity measurements. The assumed geometry of Pt(II) and Pd(II) complexes was square planar where the ligand was tridentately coordinated via the quinoline and imine nitrogen atoms and the selenium atom. The cytotoxic activity of the new Pt(II) and Pd(II) compounds, as well as of some previously synthesized Cd(II), Zn(II) and Ni(II) complexes with the same or analogous ligand, was tested against a panel of three human cancer cell lines: human cervix carcinoma cells (HeLa), human melanoma cells (FemX) and breast cancer cells (MDA-361). All investigated compounds, except Pt(II) complex, possess a strong dose-dependent cytotoxic activity of the same order of magnitude as cisplatin (CDDP). The investigation of potential of these compounds to induce HeLa cell cycle perturbations was also evaluated.

Synthesis, structure and characterization of novel Cd(II) and Zn(II) complexes with the condensation product of 2-formylpyridine and selenosemicarbazide Antiproliferative activity of the synthesized complexes and related selenosemicarbazone complexes.

Two novel Cd(II) and Zn(II) complexes with the condensation product of 2-formylpyridine and selenosemicarbazide were synthesized. The structure of Cd(II) complex was determined by X-ray crystallography. The ligand is coordinated in a neutral form via pyridine and azomethine nitrogen atoms and the selenium donor. The cadmium ion completes its five-coordination by two chloride ligands, forming a square-pyramidal geometry. The structure of Zn(II) complex was established by analysis of spectroscopic data, which indicated coordination of the ligand as a bidentate via the selenium and the azomethine nitrogen atoms. The cytotoxic activity of the newly synthesized complexes, as well as if five structurally related complexes and the ligand evaluated against eight tumor cell lines. The new Cd(II) complex showed the highest activity similar to cisplatin with IC50 less than 10muM for all cell lines. Cell cycle distribution and apoptosis study showed that Cd(II) complex and cisplatin might have some similarity in anticancer activity, which was not the case for cisplatin and other studied complexes. Effects of the complexes on matrix metalloproteinases (MMPs) MMP-9 and MMP-2 was also studied. Cd(II) and Zn(II) complexes and cisplatin increased MMP-2 activity in supernatants of tested cells, while Ni(II) complex with the same ligand decreased the activity, implying a possible activity in preventing tumor invasion and metastasis processes.

Synthesis and biological evaluation of some 17-picolyl and 17-picolinylidene androst-5-ene derivatives

Starting from dehydroepiandrosterone (1) 17-picolyl (2), 17-picolinylidene (7), 17-picolinylidene-16-one (10 and 11), and 17-picolyl-16-one (15) derivatives of androst-5-ene were synthesized in one, two, four and five steps respectively. By the Oppenauer oxidation or dehydration of 2, 7, 10, and 11 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), the corresponding A and B ring modified derivatives 3, 5, 6, 8, 9, and 12-14 were obtained. The structure of 2 was unambiguously proved by the appropriate X-ray structural analysis. Compounds 3, 5, 9, 12-14 showed inhibitory activity against the enzyme aromatase. Antibacterial activity, toxicity to brine shrimp Artemia salina, antitumor activity against three tumor cell lines (human cervix carcinoma HeLa cells, human melanoma FemX cells, and human myelogenous leukemia K562 cells) and toxicity against peripheral blood mononuclear cells were evaluated. Three tested compounds, namely 11, 13, and 15, showed strong activity against all three cell lines, the IC(50) values being in the range of 4-10 microM.

Chemical Composition of the Brown Alga Padina pavonia (L.) Gaill. from the Adriatic Sea

Abstract The chemical composition of the brown alga Padina pavonia (L.) Gaill. from the southern Adriatic Sea was investigated. Twelve sterols were identified in the sterol fraction, the main ones being cholesterol and fucosterol. The main fatty acids in the lipids were also identified. The most abundant fatty acid was palmitic acid, followed by oleic and myristic acids. The concentration of polyunsaturated fatty acids was unusually low for a marine alga. By GC/MS analysis of the volatile and polar fractions, 40 compounds were identified. Some of them probably possess defensive functions. In the volatile fraction free fatty acids, aromatic esters, benzyl alcohol and benzaldehyde predominated. Low concentrations of terpenoids, phenols and sulfur containing compounds were also identified. The n-butanol extract contained mainly fatty acids and polyols. Some of the extracts had an antibacterial activity.

New androst-4-en-17-spiro-1,3,2-oxathiaphospholanes. Synthesis, assignment of absolute configuration and in vitro cytotoxic and antimicrobial activities

The reactions of 17α-hydroxyprogesterone with Lawessons reagent (LR) in toluene, CH(2)Cl(2) and/or CCl(4) gave, depending on the duration of the reaction, two diastereoisomeric androst-4-en-17-spiro-1,3,2-oxathiaphospholane-2-sulfide pairs 2a,b and 3a,b in approximately 7:3 ratio, differing in configuration at the phosphorus atom. A parallel analysis of heteronuclear 2D (1)H-(13)C spectra (HSQC and HMBC) and homonuclear 2D spectra (NOESY) enabled complete (1)H and (13)C assignments of each isomer. Also, analysis of NOESY correlations provided evidence for the preferred conformation. X-ray analysis of 3a confirmed the structure and absolute configuration on phosphorus. A pathway for the formation of 1,3,2-oxathiaphospholane ring was proposed. Cytotoxic activity in vitro was tested against three tumor cell lines (human cervix carcinoma HeLa cells and two human breast carcinoma MDA-MB-361 and MDA-MB-453 cells). Compound 3a and mixture 3a,b showed a moderate activity against HeLa and MDA-MB-453 cell lines while against MDA-MB-361 cell line all tested compounds exerted very weak cytotoxic effect. Antimicrobial activity against Gram-positive, Gram-negative bacteria and fungal cells, toxicity to brine shrimp Artemia salina, were evaluated. All tested compounds showed strong antifungal activity.

Synthesis, characterization and biological activity of three square-planar complexes of Ni(II) with ethyl (2E)-2-[2-(diphenylphosphino)benzylidene]hydrazinecarboxylate and monodentate pseudohalides.

Three square-planar complexes of nickel(II) with the tridentate condensation derivative of 2-(diphenylphosphino)benzaldehyde and ethyl carbazate, and monodentate pseudohalides, have been synthesized. Their crystal structures have been determined. All the complexes showed a significant antifungal activity, while only the azido complex displayed antibacterial activity. All the complexes were cytotoxic to a panel of six tumor cell lines, the azido complex showing a similar activity as cisplatin to leukemia cell line K562 and lower toxicity to normal MRC-5 cells than that anticancer agent. The complexes interfered with cell cycle of tumor cells and induced plasmid DNA cleavage.

Zn(II) complex with 2-quinolinecarboxaldehyde selenosemicarbazone: synthesis, structure, interaction studies with DNA/HSA, molecular docking and caspase-8 and -9 independent apoptose induction

A new Zn(II)-based potential chemotherapeutic agent was synthesized from the ligand 2-quinolinecarboxaldehyde selenosemicarbazone (Hqasesc). Single crystal X-ray diffraction analysis showed that the Zn(II) complex consists of a cation [Zn(Hqasesc)2]2+, two perchlorate anions and one ethanol solvent molecule. The interaction of calf thymus (CT) DNA and human serum albumin (HSA) with the Zn(II) complex was explored using absorption and emission spectral methods, and also has been supported by molecular docking studies. The complex has more affinity to minor DNA groove than major, with no significant intercalation. The HSA interaction studies of the complex revealed the quenching of the intrinsic fluorescence of the HSA through a static quenching mechanism. The antitumor activity of the ligand and the complex against pancreatic adenocarcinoma cell line (AsPC-1) and acute monocytic leukemia (THP-1) cells was evaluated. Both compounds are strong concentration-dependent apoptosis inducers in THP-1 cells. While Hqasesc in AsPC-1 cells induces apoptosis only at the highest concentration, treatment with the Zn complex shows a concentration-dependent apoptotic response, where the treated cells are arrested in the G1-to-S phase accompanied with extensive activation of caspase-8 and -9. These results indicate that the ligand and Zn(II) complex display cell phenotype specific activity.

Study of heterogeneous equilibria in saturated aqueous solutions of some 7-chloro-1,4-benzodiazepines

Acid-base equilibria in heterogeneous and homogeneous systems of some sparingly soluble benzodiazepines (diazepam, prazepam, chlordiazepoxide and medazepam) were investigated in aqueous solution and the corresponding equilibrium constants were determined by the application of pH-metric, spectrophotometric and solubility methods. The sites of protonation were predicted on the basis of the analysis of the corresponding carbon-13 nuclear magnetic resonance spectra. In addition, buffer characteristics of saturated aqueous solutions of these drugs in the presence of the solid phase were investigated and it was established that they possess a very high buffer capacity over a specific pH range.