Anja Bodtke

Studies on the photoactivation of two cytotoxic trans,trans,trans-diazidodiaminodihydroxo-Pt(IV) complexes.

Light-activation of metal ion complexes to cytotoxic species is of interest due to the potential use in anticancer therapy. Two platinum complexes, trans,trans,trans-[Pt(IV)(N(3))(2)(OH)(2)(NH(3))(2)] (3) and trans,trans,trans-[Pt(IV)(N(3))(2)(OH)(2)(py)(NH(3))] (4) were irradiated with either UV (λ = 366 nm) or white fluorescent light and the various photochemical and photobiological phenomena were characterized. HPLC coupled to UV/Vis and MS detection was used to identify photochemical species resulting from irradiation of 4 with UV and white light. These studies showed that various Pt(IV) and Pt(II) products formed during the photolysis. The mass spectra of Pt(IV) complexes showed Pt ions in both the positive as well as the negative mode while Pt(II) complexes resulted in only positively charged Pt(III) ions. Since cellular DNA is considered to be a key target for platinum antitumor drugs, the irreversible platination of calf thymus DNA by the photoactivated Pt(IV) complexes was followed by Atomic Adsorption spectrometry (AAS). The effect of adding chloride or biological reducing agents glutathione (GSH) and ascorbic acid on the rates of DNA platination where also studied. Upon activation by light, both compounds show similar binding behaviour to DNA, but the rates of DNA platination for 3 were faster than for 4. Both chloride and GSH protected DNA from platination by the photoactivated compounds; consistent with the trapping of reactive aqua-Pt species. The presence of ascorbate increased the level of platinum bound to DNA for photoactivated 4 but not for 3. Without photoactivation, little or no DNA platination was observed, either with or without ascorbate or GSH. Cytotoxicity studies with two human cancer cell lines underline the photochemotherapeutic potential of these compounds. Striking is the increase in cytotoxic potency with the replacement of an ammine by a pyridine ligand.

Triterpene glycosides from the leaves of Pittosporum angustifolium.

Phytochemical investigation of the leaves of Pittosporum angustifolium resulted in the isolation and structural elucidation of nine new triterpene saponins, named pittangretosides A-I (1-9), together with a known compound (10). Mainly by NMR and HRESIMS experiments, eight compounds were identified as A1-barrigenol glycosides (1-7, 10), whereas two compounds exhibited an unusual 17,22-seco-backbone of oleanolic acid (8, 9). All compounds were evaluated for their in vitro cytotoxicities against human urinary bladder carcinoma cells (5637). Only compounds with an angeloyl-residue at C-22 of the aglycone (1-4 and 10) showed antiproliferative effects with IC50 values of 4.1, 5.2, 2.1, 17.9, and 2.4 µM, respectively.

Cytotoxic and antimicrobial activities of Cu(II), Co(II), Pt(II) and Zn(II) Complexes with N,O-chelating heterocyclic carboxylates.

A series of Cu(II), Co(II), Pt(II) and Zn(II) coordination compounds has been prepared by the reaction of the metal chlorides with pyrazine‐2‐carboxylic acid, pyridine‐2‐carboxylic acid, imidazole‐4‐carboxylic acid, benzimidazole‐2‐carboxylic acid and 1‐methylimidazole‐2‐carboxylic acid. The complexes were characterized by IR, UV‐VIS, elemental analysis, and some by 1H‐NMR, X‐ray crystallography, HPLC and LC/MS spectroscopy. All complexes consist of a 2:1 ratio of ligand to metal ion. IR and X‐ray crystallography show that coordination is through the nitrogen and carboxylate oxygen donor atoms of the ligand to form chelating rings. DFT calculations predict that the trans‐coordinated isomers are thermodynamically more stable than their cis‐forms. Only one of five complexes studied by X‐ray crystallography, Cu(II) complex of 1‐methylimidazole‐2‐carboxylic acid showed a cis‐configured metal ion center. HPLC analysis indicated that Pt(II) complex of 1‐methylimidazole‐2‐carboxylic acid is dominated (>90%) by the trans‐configured complex. All other complexes showed one isomer, presumably the trans‐form. The cytotoxic activity was investigated in human cancer cell lines in vitro; only the Pt(II) complexes were active. The antimicrobial activity against four bacterial strains and one fungi was estimated by the MIC method and best results were found amongst the Co(II) complexes. These results indicate that trans‐coordinated bischelating N,O‐heterocyclic carboxylates of Pt(II) are an interesting new class of potential antitumor agents.

Cytotoxic saponins from the seeds of Pittosporum angustifolium.

Three new acylated R1-barrigenol triterpene glycosides, 1 - 3, were isolated from the seeds of Pittosporum angustifolium Lodd. together with four known glycosides, 4 - 7, containing R1- and A1-barrigenol backbones. On the basis of spectroscopic, spectrometric, and chemical analyses the novel compounds were named pittangretosides N- P and established as 21ß-acetoxy- 22α-angeloyloxy- (1), 21ß-acetoxy-22α-(2-acetoxy-2-methylbutyroyloxy)- (2), and 21ß-(2-methylbutyroyloxy)- 22α-acetoxy-3ß-[b-D-glucopyranosyl- (1→2)]-[α-L-arabinopyranosyl-(1→3)]-[α- L-arabinofuranosyl-(1!4)]-ß-D-glucuronopyranosyloxyolean-12-ene-15α,16α,28-triol (3). Evaluation of the in vitro cytotoxicity against three tumour cell lines and one non-tumourigenic cell line revealed antiproliferative effects with IC50 values in a range of 1:74 - 34:1 μM

Effects of cytotoxic cis - and trans -diammine monochlorido platinum(II) complexes on selenium-dependent redox enzymes and DNA

Here we present the preparation of 14 pairs of cis- and trans-diammine monochlorido platinum(II) complexes, coordinated to heterocycles (i.e., imidazole, 2-methylimidazole and pyrazole) and linked to various acylhydrazones, which were designed as potential inhibitors of the selenium-dependent enzymes glutathione peroxidase 1 (GPx-1) and thioredoxin reductase 1 (TrxR-1). However, no inhibition of bovine GPx-1 and only weak inhibition of murine TrxR-1 was observed in in vitro assays. Nonetheless, the cis configured diammine monochlorido Pt(II) complexes exhibited cytotoxic and apoptotic properties on various human cancer cell lines, whereas the trans configured complexes generally showed weaker potency with a few exceptions. On the other hand, the trans complexes were generally more likely to lack cross-resistance to cisplatin than the cis analogues. Platinum was found bound to the nuclear DNA of cancer cells treated with representative Pt complexes, suggesting that DNA might be a possible target. Thus, detailed in vitro binding experiments with DNA were conducted. Interactions of the compounds with calf thymus DNA were investigated, including Pt binding kinetics, circular dichroism (CD) spectral changes, changes in DNA melting temperatures, unwinding of supercoiled plasmids and ethidium bromide displacement in DNA. The CD results indicate that the most active cis configured pyrazole-derived complex causes unique structural changes in the DNA compared to the other complexes as well as to those caused by cisplatin, suggesting a denaturation of the DNA structure. This may be important for the antiproliferative activity of this compound in the cancer cells.

Three‐Component Aminoalkylations Yielding Dihydronaphthoxazine‐Based Sirtuin Inhibitors: Scaffold Modification and Exploration of Space for Polar Side‐Chains

Nonpolar derivatives of heterocyclic aromatic screening hits like the non‐selective sirtuin inhibitor splitomicin tend to be poorly soluble in biological fluids. Unlike sp3‐rich natural products, flat aromatic compounds are prone to stacking and often difficult to optimize into leads with activity in cellular systems. The aim of this work was to identify anchor points for the introduction of sp3‐rich fragments with polar functional groups into the newly discovered active (IC50 = 5 μM) but nonpolar scaffold 1,2‐dihydro‐3H‐naphth[1,2‐e][1,3]oxazine‐3‐thione by a molecular modeling approach. Docking studies were conducted with structural data from crystallized human SIRT2 enzyme. Subsequent evaluation of the in silico hypotheses through synthesis and biological evaluation of the designed structures was accomplished with the aim to discover new SIRT2 inhibitors with improved aqueous solubility. Derivatives of 8‐bromo‐1,2‐dihydro‐3H‐naphth[1,2‐e][1,3]oxazine‐3‐thione N‐alkylated with a hydrophilic morpholino‐alkyl chain at the thiocarbamate group intended for binding in the acetyl‐lysine pocket of the enzyme appeared to be promising. Both the sulfur of the thiocarbamate and the bromo substituent were assumed to result in favorable hydrophobic interactions and the basic morpholino‐nitrogen was predicted to build a hydrogen bond with the backbone Ile196. While the brominated scaffold showed moderately improved activity (IC50 = 1.8 μM), none of the new compounds displayed submicromolar activity. Synthesis and characterization of the new compounds are reported and the possible reasons for the outcome are discussed.

Taraxastane-type triterpene saponins isolated from Pittosporum angustifolium Lodd.

Abstract Two new taraxastane-type triterpene saponins, named pittangretosides L (1) and C1 (2), were isolated from the leaves of Pittosporum angustifolium Lodd. Their structures were established by NMR spectroscopic, mass spectrometric and chemical means. The in vitro cytotoxicity was evaluated against four cell lines. The compounds exhibited no cytotoxic activity up to a concentration of 130 μm.

Oxidation Potentials of N‐Modified Derivatives of the Analgesic Flupirtine Linked to Potassium KV7 Channel Opening Activity But Not Hepatocyte Toxicity

Openers of neuronal voltage‐gated potassium channels (KV) are of interest as therapeutic agents for treating pain (flupirtine) and epilepsy (retigabine). In an effort to better understand the mechanisms of action and toxicity of flupirtine, we synthesized nine novel analogues with varying redox behavior. Flupirtine can be oxidatively metabolized into azaquinone diimines; thus, the oxidation potentials of flupirtine and its analogues were measured by cyclic voltammetry. KV7.2/3 (KCNQ2/3) opening activity was determined by an established assay with HEK293 cells overexpressing these channels. A link was found between the oxidation potentials of the compounds and their EC50 values for potassium channel opening activity. On the other hand, no correlation was observed between oxidation potentials and cytotoxicity in cultures of transgenic mouse hepatocytes (TAMH). These results support the idea that oxidative metabolites of flupirtine contribute to the mechanism of action, similar to what was recently proposed for acetaminophen (paracetamol), but not to hepatotoxicity.

New Mono- and Bisdesmosidic Triterpene Glycosides from Pittosporum angustifolium Lodd

Abstract Fifteen new mono- and bisdesmosidic triterpene saponins, named pittangretosides J, K, M, Q- Z, A1, and B1, along with three known compounds were isolated from the leaves of Pittosporum angustifolium. By spectroscopic, mass spectrometric and chemical evidence, their structures were established as glycosides of A1- and R1-barrigenol, barringtogenol C and camelliagenin A backbones

Tractable synthesis of multipurpose screening compounds with under-represented molecular features for an open access screening platform

The layout of multipurpose screening libraries must address criteria for the compounds such as novelty, diversity potential, innovative design, and last but not least synthetic tractability. While academic compound collections are often innovative, novel, and highly divers, synthesis of analogs or larger substance quantities is often hampered by complex multistep syntheses with low overall yields. In addition, covalently binding compounds and interaction motifs designed to bind metal ions were discriminated against by the paradigm that these interaction types must almost inevitably lead to toxic effects. We would like to challenge this hypothesis. The lack of such interactions could be a reason for frequent failure in the disclosure of hits for hitherto undruggable target proteins using commercially available screening collections. Thus, easily synthesizable screening candidates equipped to bind covalently to nucleophiles or to metalloenzymes by chelation are under-represented in public access screening libraries. Within this work, we present the synthesis and deposition of 88 compounds with five distinct functional classes, each of which features under-represented screening motifs, for example, metal ion complexation, reversible covalent binding, or halogen bonding. The collection includes acetohydrazides, acylhydrazones, propylene glycol ethers, 2-cyanoacetamides, and 2-cyanoacrylamides. The rational for the synthesis of most of the compounds was recently published by our group and is now supplemented by additional compounds reported here for the first time. The public access disposition enables academic research groups to collectively expand the druggable space and interdisciplinary collaborate within the scientific field.Graphical Abstract