Three novel complexes of deprotonated diflunisal (dif) with neocuproine (neo) were synthesized and characterized via elemental, spectral (UV-vis, FTIR, fluorescence, and mass spectrometry), and single-crystal X-ray diffraction analyses. Although the compounds shared a similar composition of [MCl(dif)(neo)], where M represents Zn(II) (1), Co(II) (2) and Cu(II) (3), only 1 and 2 were isostructural, while 3 differed in both the molecular and supramolecular structures. In all three complex molecules, the central atom is coordinated by two nitrogen atoms of neo in a bidentate chelate mode, and one chlorido ligand and dif is bonded in either a monodentate mode via one oxygen atom of the carboxylate in 1 and 2 or in a bidentate chelate mode via both carboxylate oxygen atoms in 3. All three compounds demonstrated remarkable antiproliferative activity against human prostate (PC-3), colon (HCT116) and breast (MDA-MB-468) cancer cell lines with IC50 values in the nanomolar range, with the lowest values observed in the case of PC-3 and MDA-MB-468 with 2 (20.0 nM) and 3 (31.1 nM), respectively. Moreover, complex 2, as the most active, was further investigated for its potential to induce perturbations in the cell cycle of PC-3 cells. The results indicated an induction of caspase-independent apoptosis. The interaction of the complexes with genomic DNA isolated from the respective cancer cell lines was evaluated for the intercalative mode, with binding strength correlated with the antiproliferative activity against PC-3 and MDA-MB-468 cancer cell lines.

For the development of anticancer drugs with higher activity and reduced toxicity, two approaches were combined: preparation of platinum(IV) complexes exhibiting higher stability compared to their platinum(II) counterparts and loading them into mesoporous silica SBA-15 with the aim to utilise the passive enhanced permeability and retention (EPR) effect of nanoparticles for accumulation in tumour tissues. Three conjugates based on a cisplatin scaffold bearing the anti-inflammatory drugs naproxen, ibuprofen or flurbiprofen in the axial positions (1, 2 and 3, respectively) were synthesised and loaded into SBA-15 to afford the mesoporous silica nanoparticles (MSNs) SBA-15|1, SBA-15|2 and SBA-15|3. Superior antiproliferative activity of both free and immobilised conjugates in a panel of four breast cancer cell lines (MDA-MB-468, HCC1937, MCF-7 and BT-474) with markedly increased cytotoxicity with respect to cisplatin was demonstrated. All compounds exhibit highest activity against the triple-negative cell line MDA-MB-468, with conjugate 1 being the most potent. However, against MCF-7 and BT-474 cell lines, the most notable improvement was found, with IC50 values up to 240-fold lower than cisplatin. Flow cytometry assays clearly show that all compounds induce apoptotic cell death elevating the levels of both early and late apoptotic cells. Furthermore, autophagy as well as formation of reactive oxygen species (ROS) and nitric oxide (NO) were elevated to a similar or greater extent than with cisplatin.

Stapled peptides derived from the Ugi macrocyclization comprise a special class of cyclopeptides with an N-substituted lactam bridge cross-linking two amino acid side chains. Herein we report a comprehensive analysis of the structural factors influencing the secondary structure of these cyclic peptides in solution. Novel insights into the s-cis/s-trans isomerism and the effect of N-functionalization on the conformation are revealed.

The enormous diversity of terpenes found in nature is generated by enzymes known as terpene synthases, or cyclases. Some are also known for their ability to convert a single substrate into multiple products. This review comprises monoterpene and sesquiterpene synthases that are multiproduct in nature along with the regulation factors that can alter the product specificity of multiproduct terpene synthases without genetic mutations. Variations in specific assay conditions with focus on shifts in product specificity based on change in metal cofactors, assay pH and substrate geometry are described. Alterations in these simple cellular conditions provide the organism with enhanced chemodiversity without investing into new enzymatic architecture. This versatility to modulate product diversity grants organisms, especially immobile ones like plants with access to an enhanced defensive repertoire by simply altering cofactors, pH level and substrate geometry.

A multicomponent macrocyclization strategy towards cyclic lipopeptides is described. The approach relies on the utilization of the Ugi and Passerini multicomponent reactions for the cyclization of peptides and oxo-peptides, and here it is employed for the construction of a small library of analogues of the natural products mycosubtilin and surfactin A. A key feature of this method is the simultaneous incorporation of either one or two exocyclic lipid tails along with the macrocyclic ring closure, which is only possible due to the multicomponent nature of the macrocyclization step. The evaluation of the anticancer activity of the lipopeptide library showed that the installation of a second lipid moiety in the surfactin scaffold leads to a more potent cytotoxicity in cancer cells. This is a new example of the multicomponent reaction potential in rapidly producing natural product analogues for biological screening.

SBA-15|Sn3, a mesoporous silica-based material (derivative of SBA-15) loaded with an organotin compound Ph3Sn(CH2)3OH (Sn3), possesses improved antitumor potential against the A2780 high-grade serous ovarian carcinoma cell line in comparison to Sn3. It is demonstrated that both the compound and the nanostructured material are internalized by the A2780 cells. A similar mode of action of Sn3 and SBA-15|Sn3 against the A2780 cell line was found. Explicitly, induction of apoptosis, caspase 2, 3, 8 and 9 activation, accumulation of cells in the hypodiploid phase as well as accumulation of ROS were observed. Interestingly, Sn3 loaded in the mesoporous silica-based material needed to reach a concentration 3.5 times lower than the IC50 value of the Sn3 compound, pointing out a higher effect of the SBA-15|Sn3 than Sn3 alone. Clonogenic potential, growth in 3D culture as well as mobility of cells were disturbed in the presence of SBA-15|Sn3. Such behavior could be associated with the suppression of p-38 MAPK. Less profound effect of Sn3 compared to SBA-15|Sn3 could be attributed to a different regulation of p-38 and STAT-3, which are mainly responsible for an appropriate cellular response to diverse stimuli or metastatic properties.

For the first time, spin-labelled coumpounds have been obtained by isonitrile-based multi component reactions (IMCRs). The typical IMCR Ugi-protocols offer a simple experimental setup allowing structural variety by which labelled diketopiperazines (DKPs) and peptide–peptoid chimera have been synthesized. The reaction keeps the paramagnetic spin label intact and offers a simple and versatile route to a large variety of new and chemically diverse spin labels.

The multiproduct sesquiterpene synthase MtTPS5 from Medicago truncatula catalyzes the conversion of farnesyl diphosphate (FDP) into a complex mixture of 27 terpenoids. 3-Bromo substrate analogues of geranyl diphosphate (3-BrGDP) and farnesyl diphosphate (3-BrFDP) were evaluated as substrates of MTPS5 enzyme. Kinetic studies demonstrated that these compounds were highly potent competitive inhibitors of the MtTPS5 enzyme with fast binding and slow reversibility. Since there is a lack of knowledge about the crystal structure of multiproduct terpene synthases, these molecules might be ideal candidates for obtaining a co-crystal structure with multiproduct terpene synthases. Due to the structural and mechanistic similarity between various terpene synthases we expect these 3-bromo isoprenoids to be ideal probes for crystal structure studies.

Correction for ‘Synthesis, cytotoxic and hydrolytic studies of titanium complexes anchored by a tripodal diamine bis(phenolate) ligand’ by Sónia Barroso et al., Dalton Trans., 2014, 43, 17422–17433.

Increasing the diversity of peptide cyclization methods is an effective way of accessing new types of macrocyclic chemotypes featuring a wide variety of ring sizes and topologies. Multicomponent reactions (MCRs) are processes capable of generating great levels of molecular diversity and complexity at low synthetic cost. In an attempt to further exploit MCRs in the field of cyclopeptides, we describe a bidirectional multicomponent approach for the synthesis of N-alkylated macrocyclic peptides of varied sequences and cross-linking positions. The process relies on the execution of two Ugi reactions between peptide diacids and diisocyanides. Varying the amino component enabled the installation of exocyclic elements of diversity, while skeletal diversity was created through different side chain and backbone cyclizations. This procedure shows prospects for the rapid scanning of the chemical space of macrocyclic peptides for applications in chemical biology and drug discovery.