The Synthesis and Biological Evaluation of Multifunctionalised Derivatives of Noscapine as Cytotoxic Agents

Noscapine, a phthalideisoquinoline alkaloid derived from Papaver somniferum, is a well‐known antitussive drug that has a relatively safe in vitro toxicity profile. Noscapine is also known to possess weak anticancer efficacy, and since its discovery, efforts have been made to design derivatives with improved potency. Herein, the synthesis of a series of noscapine analogues, which have been modified in the 6′, 9′, 1 and 7‐positions, is described. In a previous study, replacement of the naturally occurring N‐methyl group in the 6′‐position with an N‐ethylaminocarbonyl was shown to promote cell‐cycle arrest and cytotoxicity against three cancer cell lines. Here, this modification has been combined with other structural changes that have previously been shown to improve anticancer activity, namely halo substitution in the 9′‐position, regioselective O‐demethylation to reveal a free phenol in the 7‐position, and reduction of the lactone to the corresponding cyclic ether in the 1‐position. The incorporation of new aryl substituents in the 9′‐position was also investigated. The study identified interesting new compounds able to induce G2/M cell‐cycle arrest and that possess cytotoxic activity against the human prostate carcinoma cell line PC3, the human breast adenocarcinoma cell line MCF‐7, and the human pancreatic epithelioid carcinoma cell line PANC‐1. In particular, the ethyl urea cyclic ether noscapinoids and a compound containing a 6′‐ethylaminocarbonyl along with 9′‐chloro, 7‐hydroxy and lactone moieties exhibited the most promising biological activities, with EC₅₀ values in the low micromolar range against all three cancer cell lines, and these derivatives warrant further investigation.     

Structural Optimization of Berberine as a Synergist to Restore Antifungal Activity of Fluconazole against Drug‐Resistant Candida albicans

We have conducted systematic structural modification, deconstruction, and reconstruction of the berberine core with the aim of lowering its cytotoxicity, investigating its pharmacophore, and ultimately, seeking novel synergistic agents to restore the effectiveness of fluconazole against fluconazole‐resistant Candida albicans. A structure–activity relationship study of 95 analogues led us to identify the novel scaffold of N‐(2‐(benzo[d][1,3]dioxol‐5‐yl)ethyl)‐2‐(substituted phenyl)acetamides 7 a – l , which exhibited remarkable levels of in vitro synergistic antifungal activity. Compound 7 d (N‐(2‐(benzo[d][1,3]dioxol‐5‐yl)ethyl)‐2‐(2‐fluorophenyl)acetamide) significantly decreased the MIC₈₀ values of fluconazole from 128.0 μg mL^?1 to 0.5 μg mL^?1 against fluconazole‐resistant C. albicans and exhibited much lower levels of cytotoxicity than berberine toward human umbilical vein endothelial cells.     

Design and Synthesis of a Series of Piperazine‐1‐carboxamidine Derivatives with Antifungal Activity Resulting from Accumulation of Endogenous Reactive Oxygen Species

In this study, we screened a library of 500 compounds for fungicidal activity via induction of endogenous reactive oxygen species (ROS) accumulation. Structure–activity relationship studies showed that piperazine‐1‐carboxamidine analogues with large atoms or large side chains substituted on the phenyl group at the R³ and R⁵ positions are characterized by a high ROS accumulation capacity in Candida albicans and a high fungicidal activity. Moreover, we could link the fungicidal mode of action of the piperazine‐1‐carboxamidine derivatives to the accumulation of endogenous ROS.     

Discovery of New Classes of Compounds that Reactivate Acetylcholinesterase Inhibited by Organophosphates

Acetylcholinesterase (AChE) that has been covalently inhibited by organophosphate compounds (OPCs), such as nerve agents and pesticides, has traditionally been reactivated by using nucleophilic oximes. There is, however, a clearly recognized need for new classes of compounds with the ability to reactivate inhibited AChE with improved in vivo efficacy. Here we describe our discovery of new functional groups—Mannich phenols and general bases—that are capable of reactivating OPC‐inhibited AChE more efficiently than standard oximes and we describe the cooperative mechanism by which these functionalities are delivered to the active site. These discoveries, supported by preliminary in vivo results and crystallographic data, significantly broaden the available approaches for reactivation of AChE.     

Synthesis and Biological Evaluation of Papain‐Family Cathepsin L‐Like Cysteine Protease Inhibitors Containing a 1,4‐Benzodiazepine Scaffold as Antiprotozoal Agents

Novel papain‐family cathepsin L‐like cysteine protease inhibitors endowed with antitrypanosomal and antimalarial activity were developed, through an optimization study of previously developed inhibitors. In the present work, we studied the structure–activity relationships of these derivatives, with the aim to develop new analogues with a simplified and more synthetically accessible structure and with improved antiparasitic activity. The structure of the model compounds was significantly simplified by modifying or even eliminating the side chain appended at the C3 atom of the benzodiazepine scaffold. In addition, a simple methylene spacer of appropriate length was inserted between the benzodiazepine ring and the 3‐bromoisoxazoline moiety. Several rhodesain and falcipain‐2 inhibitors displaying single‐digit micromolar or sub‐micromolar antiparasitic activity against one or both parasites were identified, with activities that were one order of magnitude more potent than the model compounds.     

Synthesis and Pharmacological Evaluation of Dimeric Follicle‐Stimulating Hormone Receptor Antagonists

A series of homo‐ and heterodimeric compounds encompassing the follicle‐stimulating hormone receptor (FSHR) antagonist (R)‐ 1 and its inactive conformer (S)‐ 1 connected through ethylene glycol spacers of various lengths is described. Evaluation of these compounds reveals that dimeric compounds, with a spacer of sufficient length, bearing two active copies of the antagonist are more potent relative to dimeric compounds in which one of the active pharmacophores is replaced by an inactive conformer. Interestingly, the opposite trend is observed if a short spacer is used, indicating that these compounds may be valuable tools to study FSHR dimerization in greater detail.     

Synthesis and Evaluation of Bis‐Thiazolium Salts as Potential Antimalarial Drugs

An innovative therapeutic approach based on the use of dicationic derivatives was previously designed to inhibit the biosynthesis of phosphatidylcholine in Plasmodium spp. Among these, bis‐thiazolium salts were shown to block proliferation of the malaria parasite at concentrations in the low nanomolar range. However, due to unsuitable molecular properties such as the presence of the two polar heads and flexibility in the linker, these compounds have low oral bioavailability. To characterize the structural requirements of the linker that lead to more rigid analogues with fewer rotatable bonds but which retain antimalarial activity, a new series of compounds incorporating an aryl moiety and eventually oxygen atoms were prepared, and their biological activity was evaluated. Structure–activity relationships suggest that the optimal linker construct is an aromatic group with two n‐butyl chains branched at the para position; two new leads (compounds 39 and 40 ) were selected for further development.     

Bis(dipyridophenazine)(2‐(2′‐pyridyl)pyrimidine‐4‐carboxylic acid)ruthenium(II) Hexafluorophosphate: A Lesson in Stubbornness

Ruthenium complexes are currently considered to be among the most promising alternatives to platinum anticancer drugs. In this work, thirteen structural analogues and organelle/receptor‐targeting peptide bioconjugates of a cytotoxic bis(dppz)‐Ru^II complex [Ru(dppz)₂(CppH)](PF₆)₂ ( 1 ) were prepared, characterized, and assessed for their cytotoxicity and cellular localization (CppH=2‐(2′‐pyridyl)pyrimidine‐4‐carboxylic acid; dppz=dipyrido[3,2‐a:2′,3′‐c]phenazine). It was observed that structural modifications (lipophilicity, charge, and size‐based) result in the cytotoxic potency of 1 being compromised. Confocal microscopy studies revealed that unlike 1 , the screened complexes/bioconjugates do not have a preferential accumulation in mitochondria. The results of this important structure–activity relationship strongly support our initial hypothesis that accumulation in mitochondria is crucial for 1 to exert its cytotoxic action.     

Synthesis and Structure–Activity Relationships of 1‐Benzyl‐4,5,6‐trimethoxyindoles as a Novel Class of Potent Antimitotic Agents

Combretastatin A‐4 derivatives : A series of combretastatin A‐4‐derived 1‐benzyl‐4,5,6‐trimethoxyindoles was designed and prepared as a novel class of potent antimitotic agents acting through the colchicine binding site on the microtubule.

     

Synthesis and Biological Evaluation of N‐Substituted Sophocarpinic Acid Derivatives as Coxsackievirus B3 Inhibitors

A series of novel N‐substituted sophocarpinic acid derivatives was designed, synthesized, and evaluated for their anti‐enteroviral activities against coxsackievirus type B3 (CVB3) and coxsackievirus type B6 (CVB6) in Vero cells. Structure–activity relationship analysis revealed that the introduction of a benzenesulfonyl moiety on the 12‐nitrogen atom in (E)‐β,γ‐sophocarpinic acid might significantly enhance anti‐CVB3 activity. Among the derivatives, (E)‐12‐N‐(m‐cyanobenzenesulfonyl)‐β,γ‐sophocarpinic acid ( 11 m ), possessing a meta‐cyanobenzenesulfonyl group, exhibited potent activity against CVB3 with a selectivity index (SI) of 107. Furthermore, compound 11 m also showed a good oral pharmacokinetic profile, with an AUC value of 7.29 μM h^?1 in rats, and good safety through the oral route in mice, with an LD₅₀ value of >1000 mg kg^?1; these values suggest a druggable characteristic. Therefore, compound 11 m was selected for further investigation as a promising CVB3 inhibitor. We consider (E)‐β,γ‐N‐(benzenesulfonyl)sophocarpinic acids to be a novel class of anti‐CVB3 agents.     

Design,Synthesis and Biological Evaluation of Rose Bengal Analogues as SecA Inhibitors

SecA, a key component of bacterial Sec‐dependent secretion pathway, is an attractive target for exploring novel antimicrobials. Rose bengal (RB), a polyhalogenated fluorescein derivative, was found from our previous study as a potent SecA inhibitor. Here we describe the synthesis and structure–activity relationships (SAR) of 23 RB analogues that were designed by systematical dissection of RB. Evaluation of these analogues allowed us to establish an initial SAR in SecA inhibition. The antimicrobial effects of these SecA inhibitors are confirmed in experiments using E. coli and B. subtilis.     

Structure‐Based Design of Microsomal Prostaglandin E2 Synthase‐1 (mPGES‐1) Inhibitors using a Virtual Fragment Growing Optimization Scheme

A small library of 2,3‐dihydroxybenzamide‐ and N‐(2,3‐dihydroxyphenyl)‐4‐sulfonamide‐based microsomal prostaglandin E₂ synthase‐1 (mPGES‐1) inhibitors was identified following a step‐by‐step optimization of small aromatic fragments selected to interact in focused regions in the active site of mPGES‐1. During the virtual optimization process, the 2,3‐dihydroxybenzamide moiety was first selected as a backbone of the proposed new chemical entities; the identified compounds were then synthesized and biologically evaluated, identifying derivatives with very promising inhibitory activities in the micromolar range. Subsequent structure‐guided replacement of the 2,3‐dihydroxybenzamide by the N‐(2,3‐dihydroxyphenyl)sulfonamide moiety led to the identification of N‐(2,3‐dihydroxyphenyl)‐4‐biphenylsulfonamide ( 6 ), the most potent small molecule of the series (IC₅₀=0.53±0.04 μm ). The simple synthetic procedure and the possibility of enhancing the potency of this class of inhibitors through additional structural modifications pave the way for further development of new molecules with mPGES‐1‐inhibitory activity, with potential application as anti‐inflammatory and anticancer agents.     

Synthesis and Biological Evaluation of N‐Substituted Noscapine Analogues

Noscapine is a phthalideisoquinoline alkaloid isolated from the opium poppy Papaver somniferum. It has long been used as an antitussive agent, but has more recently been found to possess microtubule‐modulating properties and anticancer activity. Herein we report the synthesis and pharmacological evaluation of a series of 6′‐substituted noscapine derivatives. To underpin this structure–activity study, an efficient synthesis of N‐nornoscapine and its subsequent reduction to the cyclic ether derivative of N‐nornoscapine was developed. Reaction of the latter with a range of alkyl halides, acid chlorides, isocyanates, thioisocyanates, and chloroformate reagents resulted in the formation of the corresponding N‐alkyl, N‐acyl, N‐carbamoyl, N‐thiocarbamoyl, and N‐carbamate derivatives, respectively. The ability of these compounds to inhibit cell proliferation was assessed in cell‐cycle cytotoxicity assays using prostate cancer (PC3), breast cancer (MCF‐7), and colon cancer (Caco‐2) cell lines. Compounds that showed activity in the cell‐cycle assay were further evaluated in cell viability assays using PC3 and MCF‐7 cells.     

Synthesis and Evaluation of Osteogenic Oxysterols as Hedgehog Pathway Activators

Oxysterols (OHCs) are metabolic byproducts of cholesterol that are known to function as agonists of the Hedgehog (Hh) signaling pathway. Previously, we reported 23(S)‐hydroxycholesterol [23(S)‐OHC, 4 ] as a potent activator of Hh signaling with the ability to functionally differentiate mouse embryonic fibroblasts to an osteogenic fate. To obtain 23(S)‐OHC in quantities suitable for in vivo evaluation, we developed a revised synthetic route that decreases the number of steps and chromatographic purifications, and which also enhances the stereoselective nature of the synthesis. This new route also allows access to the C21 methyl group of the OHC scaffold, and several new analogues with varying stereochemistry at this location were evaluated for their ability to up‐regulate the Hh pathway.     

Improved 2,4‐Diarylthiazole‐Based Antiprion Agents: Switching the Sense of the Amide Group at C5 Leads to an Increase in Potency

Amide derivatives of 2,4‐diarylthiazole‐5‐carboxylic acids were synthesised and tested for efficacy in a cell line model of prion disease. A number of compounds demonstrating antiprion activity were thereby identified from the screening libraries, showing improved potency and reproducibility of results relative to amide derivatives of the related 2,4‐diphenyl‐5‐aminothiazole, which have been documented previously. Thus, 'switching' the sense of the amide bond at thiazole C5 revealed a more promising lead series of potential prion disease therapeutics. Furthermore, 3,5‐diaryl‐1,2,4‐thiadiazoles isolated as by‐products during library synthesis provided a handful of additional examples possessing an antiprion effect, thereby augmenting the set of newly identified active compounds. Evaluation of binding to cellular prion protein (PrP^C) showed only weak affinities at best, suggesting that the newly identified antiprion agents do not mediate their biological effect through direct interaction with PrP^C.     

Synthesis and Pharmacological Evaluation of SNC80 Analogues with a Bridged Piperazine Ring

To discover novel δ‐opioid receptor ligands derived from SNC80 ( 1 ), a series of 6,8‐diazabicyclo[3.2.2]nonane derivatives bearing two aromatic moieties was prepared, and the affinity toward δ, μ, and κ receptors, as well as σ receptors, was investigated. After removal of the 4‐methoxybenzyl and 2,4‐dimethoxybenzyl protecting groups, the pharmacophoric N,N‐diethylcarbamoylbenzyl residue was attached to the 6,8‐diazabicyclo[3.2.2]nonane framework to yield the designed δ receptor ligands. In a first series of compounds the benzhydryl moiety of SNC80 was dissected, and one phenyl ring was attached to the bicyclic framework. In a second series of δ ligands the complete benzhydryl moiety was introduced into the bicyclic scaffold. The determined δ receptor affinities show that compounds based on an (R)‐glutamate‐derived bicyclic scaffold possess higher δ receptor affinity than their (S)‐glutamate‐derived counterparts. Furthermore, an intact benzhydryl moiety leads to δ receptor ligands that are more potent than compounds with two separated aromatic moieties. Compound 24 , with the same spatial arrangement of substituents around the benzhydryl stereocenter as SNC80, shows the highest δ receptor affinity of this series: K_i=24 nM . Whereas the highly potent δ ligands reveal good selectivity against μ and κ receptors, the σ₁ and/or σ₂ affinities of some compounds are almost in the same range as their δ receptor affinities, such as compound 25 (σ₂: K_i=83 nM ; δ: K_i=75 nM ). In [³⁵S]GTPγS assays the most potent δ ligands 24 and 25 showed almost the same intrinsic activity as the full agonist SNC80, proving the agonistic activity of 24 and 25 . The enantiomeric 4‐benzylidene derivatives 15 and ent‐ 15 showed selective cytotoxicity toward the 5637 (bladder) and A‐427 (small‐cell lung) human tumor cell lines.