Discovery of harmiprims, harmine-primaquine hybrids, as potent and selective anticancer and antimalarial compounds.

Although cancer and malaria are not etiologically nor pathophysiologically connected, due to their similarities successful repurposing of antimalarial drugs for cancer and vice-versa is known and used in clinical settings and drug research and discovery. With the growing resistance of cancer cells and Plasmodium to the known drugs, there is an urgent need to discover new chemotypes and enrich anticancer and antimalarial drug portfolios. In this paper, we present the design and synthesis of harmiprims, hybrids composed of harmine, an alkaloid of the ß-carboline type bearing anticancer and antiplasmodial activities, and primaquine, 8-aminoquinoline antimalarial drug with low antiproliferative activity, covalently bound via triazole or urea. Evaluation of their antiproliferative activities in vitro revealed that N-9 substituted triazole-type harmiprime was the most selective compound against MCF-7, whereas C1-substituted ureido-type hybrid was the most active compound against all cell lines tested. On the other hand, dimeric harmiprime was not toxic at all. Although spectrophotometric studies and thermal denaturation experiments indicated binding of harmiprims to the ds-DNA groove, cell localization showed that harmiprims do not enter cell nucleus nor mitochondria, thus no inhibition of DNA-related processes can be expected. Cell cycle analysis revealed that C1-substituted ureido-type hybrid induced a G1 arrest and reduced the number of cells in the S phase after 24 h, persisting at 48 h, albeit with a less significant increase in G1, possibly due to adaptive cellular responses. In contrast, N-9 substituted triazole-type harmiprime exhibited less pronounced effects on the cell cycle, particularly after 48 h, which is consistent with its moderate activity against the MCF-7 cell line. On the other hand, screening of their antiplasmodial activities against the erythrocytic, hepatic, and gametocytic stages of the Plasmodium life cycle showed that dimeric harmiprime exerts powerful triple-stage antiplasmodial activity, while computational analysis showed its binding within the ATP binding site of PfHsp90.

Synthesis and Biological Evaluation of New Quinoline and Anthranilic Acid Derivatives as Potential Quorum Sensing Inhibitors.

Inhibiting quorum sensing (QS), a central communication system, is a promising strategy to combat bacterial pathogens without antibiotics. Here, we designed novel hybrid compounds targeting the PQS (Pseudomonas quinolone signal)-dependent quorum sensing (QS) of Pseudomonas aeruginosa that is one of the multidrug-resistant and highly virulent pathogens with urgent need of new antibacterial strategies. We synthesized 12 compounds using standard procedures to combine halogen-substituted anthranilic acids with 4-(2-aminoethyl/4-aminobuthyl)amino-7-chloroquinoline, linked via 1,3,4-oxadiazole. Their antibiofilm activities were first pre-screened using Gram-negative Chromobacterium violaceum-based reporter, which identified compounds 15-19 and 23 with the highest anti-QS and minimal bactericidal effects in a single experiment. These five compounds were then evaluated against P. aeruginosa PAO1 to assess their ability to prevent biofilm formation, eradicate pre-formed biofilms, and inhibit virulence using pyocyanin as a representative marker. Compound 15 displayed the most potent antibiofilm effect, reducing biofilm formation by nearly 50% and pre-formed biofilm masses by 25%. On the other hand, compound 23 exhibited the most significant antivirulence effect, reducing pyocyanin synthesis by over 70%. Thus, our study highlights the potential of 1,3,4-oxadiazoles 15 and 23 as promising scaffolds to combat P. aeruginosa. Additionally, interactive QS systems should be considered to achieve maximal anti-QS activity against this clinically relevant species.

Itaconic acid hybrids as potential anticancer agents.

In this paper, we report the synthesis of novel hybrids 2-14 based on itaconic acid and fluoroaniline, pyridine, indole and quinoline scaffolds. Itaconic acid is a naturally occurring compound with a Michael acceptor moiety, a key structural feature in several anticancer and antiviral drugs, responsible for the covalent binding of a drug to the cysteine residue of a specific protein. Aromatic parts of the hybrids also come from the substances reported as anticancer or antiviral agents. The synthetic route employed to access the amido-ester hybrids 2-13 used monomethyl itaconate or monomethyl itaconyl chloride and corresponding amines as the starting materials. Dimers 14 and 15 with two aminoindole or mefloquine moieties were prepared from itaconic acid and corresponding amino derivative, using standard coupling conditions (HATU/DIEA). All hybrids exerted anticancer effects in vitro against almost all the tumour cell lines that were evaluated (MCF-7, HCT 116, H460, LN-229, Capan-1, DND-41, HL-60, K-562, Z-138). Solid tumour cells were, in general, more responsive than the haematological cancer cells. The MCF-7 breast adenocarcinoma cell line appeared the most sensitive. Amido-ester 12 with chloroquine core and mefloquine homodimer 15 showed the highest activity with GI50 values between 0.7 and 8.6 µM. In addition, compound 15 also exerted antiviral activity against Zika virus and Coxsackievirus B4 in low micromolar concentrations.

Harmicens, Novel Harmine and Ferrocene Hybrids: Design, Synthesis and Biological Activity.

Cancer and malaria are both global health threats. Due to the increase in the resistance to the known drugs, research on new active substances is a priority. Here, we present the design, synthesis, and evaluation of the biological activity of harmicens, hybrids composed of covalently bound harmine/ß-carboline and ferrocene scaffolds. Structural diversity was achieved by varying the type and length of the linker between the ß-carboline ring and ferrocene, as well as its position on the ß-carboline ring. Triazole-type harmicens were prepared using Cu(I)-catalyzed azide-alkyne cycloaddition, while the synthesis of amide-type harmicens was carried out by applying a standard coupling reaction. The results of in vitro biological assays showed that the harmicens exerted moderate antiplasmodial activity against the erythrocytic stage of P. falciparum (IC50 in submicromolar and low micromolar range) and significant and selective antiproliferative activity against the MCF-7 and HCT116 cell lines (IC50 in the single-digit micromolar range, SI > 5.9). Cell localization experiments showed different localizations of nonselective harmicene 36 and HCT116-selective compound 28, which clearly entered the nucleus. A cell cycle analysis revealed that selective harmicene 28 had already induced G1 cell cycle arrest after 24 h, followed by G2/M arrest with a concomitant drastic reduction in the percentage of cells in the S phase, whereas the effect of nonselective compound 36 on the cell cycle was much less pronounced, which agreed with their different localizations within the cell.

Novel Harmicines with Improved Potency against Plasmodium.

Harmicines represent hybrid compounds composed of ß-carboline alkaloid harmine and cinnamic acid derivatives (CADs). In this paper we report the synthesis of amide-type harmicines and the evaluation of their biological activity. N-harmicines 5a-f and O-harmicines 6a-h were prepared by a straightforward synthetic procedure, from harmine-based amines and CADs using standard coupling conditions, 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo [4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU) and N,N-diisopropylethylamine (DIEA). Amide-type harmicines exerted remarkable activity against the erythrocytic stage of P. falciparum, in low submicromolar concentrations, which was significantly more pronounced compared to their antiplasmodial activity against the hepatic stages of P. berghei. Furthermore, a cytotoxicity assay against the human liver hepatocellular carcinoma cell line (HepG2) revealed favorable selectivity indices of the most active harmicines. Molecular dynamics simulations demonstrated the binding of ligands within the ATP binding site of PfHsp90, while the calculated binding free energies confirmed higher activity of N-harmicines 5 over their O-substituted analogues 6. Amino acids predominantly affecting the binding were identified, which provided guidelines for the further derivatization of the harmine framework towards more efficient agents.

Second generation of primaquine ureas and bis-ureas as potential antimycobacterial agents.

Here, we describe design and synthesis of twelve novel compounds bearing primaquine motif and hydroxy- or halogenamine linked by an urea or bis-urea spacer. Preparation of ureas 3a-f started with the conversion of primaquine to benzotriazolide 2 and aminolysis of the later compound by 4-(2-aminoethyl)phenol or amino alcohols bearing fluorine atom, cycloalkyl or trifluoromethyl group under microwave irradiation. The four-step sequence leading to bis-ureas 6a-f included preparation of benzotriazolide 2 and two intermediates, semicarbazide 4 and benzotriazole bis-urea 5, which upon aminolysis with the same aminophenol or amino alcohols gave the title compounds. Antimycobacterial screening detected three active compounds against Mycobacterium marinum and M. tuberculosis, namely 3b, 3f and 6f, derived from cyclobutyl amino alcohol or amino phenol.

Design, Synthesis and Biological Evaluation of Novel Primaquine-Cinnamic Acid Conjugates of the Amide and Acylsemicarbazide Type.

In this paper design and synthesis of a scaffold comprising primaquine (PQ) motif and cinnamic acid derivatives (CADs) bound directly (compounds 3a-k) or via a spacer (compounds 7a-k) are reported. In the first series of compounds, PQ and various CADs were connected by amide bonds and in the second series by acylsemicarbazide functional groups built from the PQ amino group, CONHNH spacer and the carbonyl group originating from the CADs. PQ-CAD amides 3a-k were prepared by a simple one-step condensation reaction of PQ with a series of CAD chlorides (method A) or benzotriazolides 2 (method B). The synthesis of acylsemicarbazides 7a-k included activation of PQ with benzotriazole, preparation of PQ-semicarbazide 6 and its condensation with CAD chlorides 4. All synthesized PQ-CAD conjugates were evaluated for their anticancer, antiviral and antioxidative activities. Almost all compounds from series 3 were selective towards the MCF-7 cell line and active at micromolar concentrations. The o-fluoro derivative 3h showed high activity against HeLa, MCF-7 and in particular against the SW 620 cell line, while acylsemicarbazide 7f with a benzodioxole ring and 7c, 7g and especially 7j with methoxy-, chloro- or trifluoromethyl-substituents in the para position showed high selectivity and high inhibitory activity against MCF-7 cell line at micromolar (7c, 7f, 7g) and nanomolar (7j) levels. Acylsemicarbazide derivatives with trifluoromethyl group(s) 7i, 7j and 7k showed specific activity against human coronavirus (229E) at concentrations which did not alter the normal cell morphology. The same compounds exerted the most potent reducing activity in the DPPH test, together with 7d and 7g, while methoxy (compounds 7c-e), benzodioxole (7f), p-Cl (7g) and m-CF3 (7i) acylsemicarbazides and amide 3f presented the highest LP inhibition (83%-89%). The dimethoxy derivative 7d was the most potent LOX inhibitor (IC50 = 10 µΜ). The performed biological tests gave evidence of acylsemicarbazide functional group as superior binding group in PQ-CAD conjugates.

The Pattern of Antibiotic Prescribing by Dental Practitioners in Zagreb, Croatia.

BACKGROUND: Bacterial resistance is considered a consequence of misuse or overuse of antibiotics. Dentistry significantly contributes to this increasing public health problem. The aim of this cross-sectional study was to examine the pattern of antibiotics prescribed by Croatian dentists in Zagreb area. METHODS: Out of 220 Doctors of Dental Medicine (DMDs) from Zagreb 110 responded to survey. Prior to the research an ethical approval was obtained. Participants were directly contacted. The questionnaire consisted of two parts: general data on DMDs and the part concerning indications, duration, type and dosage of antibiotic therapy. Data were processed using MS Excel and SPSS for Windows, Version 17.0. Statistical significance was tested by Fisher's exact test, chi-square test, Mann-Whitney U test and Spearman's rank correlation at the level of statistical significance p<0.05. RESULTS: During the period of two months, the doctors prescribed antibiotics to 1,500 patients, 690 (46%) were men and 810 (54%) women. The most often prescribed antibiotics were penicillin (72.5% of patients), represented mostly by amoxicillin in combination with clavulanic acid (57.6%). The most common indication for the prescribed antibiotics was periapical or periodontal abscess (44%). Definite clinical indication (71.2%) was stated as the most common reason for antibiotic prescription. Antibiotic therapy usually lasted 7 days (62.9%). The doctors prescribed daily doses of antibiotics according to the instructions for the use of specific drugs. CONCLUSION: The examined subjects prescribe antibiotics according to the curriculum taught at the School of Dental Medicine for majority of types, doses and duration of the treatments, although antibiotics over-prescription in cases without medical indication was observed. The national guidelines on antibiotic regimens are required in order to reduce unnecessary antibiotic use.

Novel 1-acyl-4-substituted semicarbazide derivatives of primaquine - synthesis, cytostatic, antiviral and antioxidative studies.

A series of novel 1,4-substituted semicarbazides 5a-g with a primaquine moiety bridged by a carbonyl group at position 1 and a cycloalkyl, aryl, benzyloxy or hydroxy substituent at position 4 were prepared and biologically evaluated. The synthetic pathways applied for preparation of the title compounds involved benzotriazole as synthetic auxiliary. Primaquine semicarbazides 5a-g and their synthetic precursors benzotriazolecarbonyl semicarbazides 4 were evaluated for cytostatic, antiviral and antioxidative activities. All compounds of the series 5 showed high selectivity towards MCF-7 cells (breast carcinoma) with IC(50) values in the low micromolar range and the most active was benzyl derivative 5c (IC(50) 1 ± 0.2 µM). The benzhydryl derivative 5e showed significant cytostatic activities towards all the tested cell lines (IC(50) 4-18 µM). The same compound was the strongest lipoxygenase inhibitor as well (51%). The highest antioxidant activity was demonstrated for the hydroxy derivative 5g and benzotriazolecarbonyl semicarbazides 4b,c (61.2-68.5%). No antiviral activity was observed against a wide variety of DNA and RNA viruses.

Antitumor mechanisms of amino Acid hydroxyurea derivatives in the metastatic colon cancer model.

The paper presents a detailed study of the biological effects of two amino acid hydroxyurea derivatives that showed selective antiproliferative effects in vitro on the growth of human tumor cell line SW620. Tested compounds induced cell cycle perturbations and apoptosis. Proteins were identified by proteomics analyses using two-dimensional gel electrophoresis coupled to mass spectrometry, which provided a complete insight into the most probable mechanism of action on the protein level. Molecular targets for tested compounds were analyzed by cheminformatics tools. Zinc-dependent histone deacetylases were identified as potential targets responsible for the observed antiproliferative effect.

Design and synthesis of harmiquins, harmine and chloroquine hybrids as potent antiplasmodial agents.

Malaria remains one of the major health problems worldwide. The lack of an effective vaccine and the increasing resistance of Plasmodium to the approved antimalarial drugs demands the development of novel antiplasmodial agents that can effectively prevent and/or treat this disease. Harmiquins represent hybrids that combine two moieties with different mechanisms of antiplasmodial activity in one molecule, i.e., a chloroquine (CQ) scaffold, known to inhibit heme polymerization and a ß-carboline ring capable of binding to P. falciparum heat shock protein 90 (PfHsp90). Here we present their synthesis, evaluation of biological activity and potential mechanism of action. The synthesized hybrids differed in the type of linker employed (triazole ring or amide bond) and in the position of the substitution on the ß-carboline core of harmine. The antiplasmodial activity of harmiquins was evaluated against the erythrocytic stage of the Plasmodium life cycle, and their cytotoxic effect was tested on HepG2 cells. The results showed that harmiquins exerted remarkable activity against both CQ-sensitive (Pf3D7) and CQ-resistant (PfDd2, PfK1, and Pf7G8). P. falciparum strains. The most active compound, harmiquine 32, displayed single-digit nanomolar IC50 value against Pf3D7 (IC50 = 2.0 ± 0.3 nM). Importantly, it also showed significantly higher activity than CQ against the resistant Plasmodium strains and had a very high selectivity index (4450). Harmiquins may act through the inhibition of heme polymerization and binding to the ATP binding site of the PfHsp90, which would explain their increased activity against the CQ-resistant Plasmodium strains. These results establish harmiquins as valuable antiplasmodial hits for future optimization.

Antiradical, chelating and antioxidant activities of hydroxamic acids and hydroxyureas.

Reactive oxygen species, along with reactive nitrogen species, may play an important role in the pathogenesis and progress of many diseases, including cancer, diabetes and sickle cell disease. It has been postulated that hydroxyurea, one of the main treatments in sickle cell disease, achieves its activity partly also through its antioxidant properties. A series of hydroxyurea derivatives of L- and D-amino acid amides and cycloalkyl-N-aryl-hydroxamic acids was synthesized and investigated for their radical scavenging activity, chelating properties and antioxidant activity. All the compounds showed exceptional antiradical activities. For example, free radical scavenging activities of investigated hydroxyureas were higher than the activity of standard antioxidant, butylated hydroxyanisole (BHA). Moreover, most of the investigated hydroxamic acids were stronger Fe²âº ion chelators than quercetin. In addition, the investigated compounds, especially hydroxamic acids, were proven to be excellent antioxidants. They were as effective as BHA in inhibiting ß-carotene-linoleic acid coupled oxidation. It is reasonable to assume that the antioxidant activity of the investigated compounds could contribute to their previously proven biological properties as cytostatic and antiviral agents.

Further investigation of harmicines as novel antiplasmodial agents: Synthesis, structure-activity relationship and insight into the mechanism of action.

The rise of the resistance of the malaria parasite to the currently approved therapy urges the discovery and development of new efficient agents. Previously we have demonstrated that harmicines, hybrid compounds composed from ß-carboline alkaloid harmine and cinnamic acid derivatives, linked via either triazole or amide bond, exert significant antiplasmodial activity. In this paper, we report synthesis, antiplasmodial activity and cytotoxicity of expanded series of novel triazole- and amide-type harmicines. Structure-activity relationship analysis revealed that amide-type harmicines 27, prepared at N-9 of the ß-carboline core, exhibit superior potency against both erythrocytic stage of P. falciparum and hepatic stages of P. berghei. Notably, harmicine 27a, m-(trifluoromethyl)cinnamic acid derivative, exhibited the most favourable selectivity index (SI = 1105). Molecular dynamics simulations revealed the ATP binding site of P. falciparum heat shock protein 90 as a druggable binding location, confirmed the usefulness of the harmine's N-9 substitution and identified favourable N-H … π interactions involving Lys45 and the aromatic phenyl unit in the attached cinnamic acid fragment as crucial for the enhanced biological activity. Thus, those compounds were identified as promising and valuable leads for further derivatization in the search of novel, more efficient antiplasmodial agents.

Emerging Trends in the Epidemiology of COVID-19: The Croatian 'One Health' Perspective.

During the four pandemic waves, a total of 560,504 cases and 10,178 deaths due to COVID-19 were reported in Croatia. The Alpha variant, dominant from March 2021 (>50% of positive samples), was rapidly replaced by Delta variants (>90%) by August 2021. Several seroprevalence studies were conducted in different populations (general population, children/adolescents, professional athletes, healthcare workers, veterinarians) and in immunocompromised patients (hemodialysis patients, liver/kidney transplant recipients). After the first pandemic wave, seroprevalence rates of neutralizing (NT) antibodies were reported to be 0.2-5.5%. Significantly higher seropositivity was detected during/after the second wave, 2.6-18.7%. Two studies conducted in pet animals (February-June 2020/July-December 2020) reported SARS-CoV-2 NT antibodies in 0.76% of cats and 0.31-14.69% of dogs, respectively. SARS-CoV-2 NT antibodies were not detected in wildlife. Environmental samples taken in the households of COVID-19 patients showed high-touch personal objects as most frequently contaminated (17.3%), followed by surfaces in patients' rooms (14.6%), kitchens (13.3%) and bathrooms (8.3%). SARS-CoV-2 RNA was also detected in 96.8% affluent water samples, while all effluent water samples tested negative. Detection of SARS-CoV-2 in humans, animals and the environment suggests that the 'One Health' approach is critical to controlling COVID-19 and future pandemics.

Harmicines - harmine and cinnamic acid hybrids as novel antiplasmodial hits.

Harmicines constitute novel hybrid compounds that combine two agents with reported antiplasmodial properties, namely ß-carboline harmine and a cinnamic acid derivative (CAD). Cu(I) catalyzed azide-alkyne cycloaddition was employed for the preparation of three classes of hybrid molecules: N-harmicines 6a-i, O-harmicines 7a-i and N,O-bis-harmicines 8a-g,i. In vitro antiplasmodial activities of harmicines against the erythrocytic stage of Plasmodium falciparum (chloroquine-sensitive Pf3D7 and chloroquine-resistant PfDd2 strains) and hepatic stage of P. berghei, as well as cytotoxicity against human liver hepatocellular carcinoma cell line (HepG2), were evaluated. Remarkably, most of the compounds exerted significant activities against both stages of the Plasmodium life cycle. The conjugation of various CADs to harmine resulted in the increased antiplasmodial activity relative to harmine. In general, O-harmicines 7 exhibited the highest activity against the erythrocytic stage of both P. falciparum strains, whereas N,O-bis harmicines 8 showed the most pronounced activity against P. berghei hepatic stages. For the latter compound, molecular dynamics simulations confirmed binding within the ATP binding site of PfHsp90, while the weaker binders, namely 6b and harmine, were found to be positioned away from this structural element. In addition, decomposition of the computed binding free energies into contributions from individual residues suggested guidelines for further derivatization of harmine towards more efficient compounds. Cytotoxicity screening revealed N-harmicines 6 as the least, and O-harmicines 7 as the most toxic compounds. Harmicines 6g, 8b and 6d exerted the most selective action towards Plasmodium over human cells, respectively. These results establish harmicines as hits for future optimisation and development of novel antiplasmodial agents.

Synthesis and biological evaluation of O-methyl and O-ethyl NSAID hydroxamic acids.

This paper reports the synthesis of O-methyl and O-ethyl NSAID hydroxamic acids, their antimicrobial activities, and their ability to inhibit urease and soybean lipoxygenase activities. Ibuprofen and fenoprofen hydroxamic acids with free hydroxy groups present the highest antimicrobial activity, while indomethacin and diclofenac analogs show significantly lower antimicrobial activity. Diclofenac hydroxamic acid 4e exerts the highest anti-urease activity. Indomethacin O-ethyl hydroxamic acid 3h and ibuprofen O-benzyl hydroxamic acid 4b exert significant inhibitory activities on soybean lipoxygenase. Fenoprofen and indomethacin O-ethyl hydroxamic acids 3b and 3h and diclofenac and indomethacin O-benzyl analogs 4g and 4i highly inhibit lipid peroxidation. The highest antioxidant activity was shown by fenoprofen derivative 3b.

Antiproliferative evaluation of various aminoquinoline derivatives.

Four classes of aminoquinoline derivatives were prepared: primaquine ureas 1a-f, primaquine bis-ureas 2a-f, chloroquine fumardiamides 3a-f and mefloquine fumardiamides 4a-f. Their antiproliferative activities against breast adeno-carcinoma (MCF-7), lung carcinoma (H460) and colon carcinoma (HCT 116 and SW620) cell lines were evaluated in vitro, using MTT cell proliferation assay. The results revealed a low activity of primaquine urea and bis-urea derivatives and high activity of all fumardiamides, with IC50 values in low micromolar range against all tested cancer cell lines.

Primaquine derivatives: Modifications of the terminal amino group.

Numerous modifications of the well-known antimalarial drug primaquine, both at the quinoline ring and at the primary amino group, have been reported, mostly to obtain antimalarial agents with improved bioavailability, reduced toxicity and/or prolonged activity. Modifications of the terminal amino group were made with the main idea to prevent the metabolic pathway leading to inactive and toxic carboxyprimaquine (follow-on strategy), but also to get compounds with different activity (repurposing strategy). The modifications undertaken until 2009 were included in a review published in the same year. The present review covers various classes of primaquine N-derivatives with diverse biological profiles, prepared in the last decade by our research group as well as the others. We have summarized the synthetic procedures applied for their preparation and discussed the main biological results. Several hits for the development of novel antiplasmodial, anticancer, antimycobacterial and antibiofilm agents were identified.

The 10th Joint Meeting on Medicinal Chemistry (JMMC 2017) Held in Dubrovnik, Croatia.

The Croatian Chemical Society was established in 1926 and has developed over the decades into a society that actively supports all chemical activities in Croatia. The Society has eight divisions, the youngest of which, the Division of Medicinal and Pharmaceutical Chemistry, was established in 2012 and immediately became a member of the European Federation of Medicinal Chemistry (EFMC). The mission of the Medicinal and Pharmaceutical Chemistry Division is the promotion and development of scientific, professional, and educational activities within the medicinal chemistry community in Croatia, as well as to build partnerships and collaborations with other primarily EU-based medicinal chemistry societies. In Croatia, medicinal chemistry research is ongoing at several institutes, including the University of Zagreb (Faculty of Science, Faculty of Pharmacy and Biochemistry, and Faculty of Chemical Engineering and Technology), national institutes of science (Ruder Boskovic Institute), and private-sector drug discovery companies (CRO Fidelta Ltd.). In order to effectively exchange knowledge, ideas, and scientific results, Croatian medicinal chemists meet twice annually.

Machine learning prioritizes synthesis of primaquine ureidoamides with high antimalarial activity and attenuated cytotoxicity.

Primaquine (PQ) is a commonly used drug that can prevent the transmission of Plasmodium falciparum malaria, however toxicity limits its use. We prepared five groups of PQ derivatives: amides 1a-k, ureas 2a-k, semicarbazides 3a,b, acylsemicarbazides 4a-k and bis-ureas 5a-v, and evaluated them for antimalarial activity in vitro against the erythrocytic stage of P. falciparum NF54. Particular substituents, such as trityl (in 2j and 5r) and methoxybenzhydryl (in 3b and 5v) were associated with a favorable cytotoxicity-to-activity ratio. To systematically link structural features of PQ derivatives to antiplasmodial activity, we performed a quantitative structure-activity relationship (QSAR) study using the Support Vector Machines machine learning method. This yielded a highly accurate statistical model (R2 = 0.776 in cross-validation), which was used to prioritize novel candidate compounds. Seven novel PQ-ureidoamides 10a-g were synthesized and evaluated for activity, highlighting the benzhydryl ureidoamides 10e and 10f derived from p-chlorophenylglycine. Further experiments on human cell lines revealed that 10e and 10f are an order of magnitude less toxic than PQ in vitro while having antimalarial activity indistinguishable from PQ. The toxicity profile of novel compounds 10 toward human cells was particularly favorable when the glucose-6-phosphate dehydrogenase (G6PD) was inhibited, while toxicity of PQ was exacerbated by G6PD inhibition. Our work therefore highlights promising lead compounds for the development of effective antimalarial drugs that may also be safer for G6PD-deficient patients. In addition, we provide computational inferences of antimalarial activity and cytotoxicity for thousands of PQ-like molecular structures.