Electron Donor-Acceptor Complex-Assisted Photochemical Conversion of O-2-Nitrobenzyl Protected Hydroxamates to Amides.

The hydroxamic acid functionality is present in various medicinal agents and has attracted special interest for synthetic transformations in both organic and medicinal chemistry. The N-O bond cleavage of hydroxamic acid derivatives provides an interesting transformation for the generation of various products. We demonstrate, herein, that O-benzyl-type protected hydroxamic acids may undergo photochemical N-O bond cleavage, in the presence or absence of a catalyst, leading to amides. Although some O-benzyl protected aromatic hydroxamates may be photochemically converted to amides in the presence of a base and anthracene as the catalyst, employing O-2-nitrobenzyl group allowed the smooth conversion of both aliphatic and aromatic hydroxamates to primary or secondary amides in good to excellent yields in the presence of an amine, bypassing the need of a catalyst. DFT and UV-Vis studies supported the effective generation of an electron donor-acceptor (EDA) complex between O-2-nitrobenzyl hydroxamates and amines, which enabled the successful product formation under these photochemical conditions. An extensive substrate scope was demonstrated, showcasing that both aliphatic and aromatic hydroxamates are compatible with this protocol, affording a wide variety of primary and secondary amides.

Nuclear receptor NR5A2 negatively regulates cell proliferation and tumor growth in nervous system malignancies.

Nervous system malignancies are characterized by rapid progression and poor survival rates. These clinical observations underscore the need for novel therapeutic insights and pharmacological targets. To this end, here, we identify the orphan nuclear receptor NR5A2/LRH1 as a negative regulator of cancer cell proliferation and promising pharmacological target for nervous system-related tumors. In particular, clinical data from publicly available databases suggest that high expression levels of NR5A2 are associated with favorable prognosis in patients with glioblastoma and neuroblastoma tumors. Consistently, we experimentally show that NR5A2 is sufficient to strongly suppress proliferation of both human and mouse glioblastoma and neuroblastoma cells without inducing apoptosis. Moreover, short hairpin RNA-mediated knockdown of the basal expression levels of NR5A2 in glioblastoma cells promotes their cell cycle progression. The antiproliferative effect of NR5A2 is mediated by the transcriptional induction of negative regulators of the cell cycle, CDKN1A (encoding for p21cip1), CDKN1B (encoding for p27kip1) and Prox1 Interestingly, two well-established agonists of NR5A2, dilauroyl phosphatidylcholine (DLPC) and diundecanoyl phosphatidylcholine, are able to mimic the antiproliferative action of NR5A2 in human glioblastoma cells via the induction of the same critical genes. Most importantly, treatment with DLPC inhibits glioblastoma tumor growth in vivo in heterotopic and orthotopic xenograft mouse models. These data indicate a tumor suppressor role of NR5A2 in the nervous system and render this nuclear receptor a potential pharmacological target for the treatment of nervous tissue-related tumors.

An Efficient Light-Mediated Protocol for the Direct Amide Bond Formation via a Novel Carboxylic Acid Photoactivation Mode by Pyridine-CBr4.

The direct amide bond formation between a carboxylic acid and an amine still constitutes a challenging reaction for both academia and industry. We demonstrate herein that several pairs of amines (halogen bond acceptors) and organohalogen sources may be used for the photochemical amidation reaction under either UVA or sunlight irradiation. Our studies led to the identification of pyridine-CBr4 as an efficient agent to perform amide synthesis under LED 370 nm irradiation, avoiding super-stoichiometric quantities. An extended substrate scope was demonstrated, showing that the widely used amino and carboxyl protecting groups are compatible with this photochemical protocol, while a number of industrially interesting products and bioactive compounds were synthesized. Direct infusion-high resolution mass spectrometry studies suggest an unprecedented type of carboxylic acid activation mode upon irradiation, involving the generation of a symmetric anhydride, an active ester with pyridine N-oxide and a mixed anhydride with hypobromous acid.

Changes in the cellular fatty acid profile drive the proteasomal degradation of α-synuclein and enhance neuronal survival.

Parkinson's disease is biochemically characterized by the deposition of aberrant aggregated α-synuclein in the affected neurons. The aggregation properties of α-synuclein greatly depend on its affinity to bind cellular membranes via a dynamic interaction with specific lipid moieties. In particular, α-synuclein can interact with arachidonic acid (AA), a polyunsaturated fatty acid, in a manner that promotes the formation of α-helix enriched assemblies. In a cellular context, AA is released from membrane phospholipids by phospholipase A2 (PLA2 ). To investigate the impact of PLA2 activity on α-synuclein aggregation, we have applied selective PLA2 inhibitors to a SH-SY5Y cellular model where the expression of human wild-type α-synuclein is correlated with a gradual accumulation of soluble oligomers and subsequent cell death. We have found that pharmacological and genetic inhibition of GIVA cPLA2 resulted in a dramatic decrease of intracellular oligomeric and monomeric α-synuclein significantly promoting cell survival. Our data suggest that alterations in the levels of free fatty acids, and especially AA and adrenic acid, promote the formation of α-synuclein conformers which are more susceptible to proteasomal degradation. This mechanism is active only in living cells and is generic since it does not depend on the absolute quantity of α-synuclein, the presence of disease-linked point mutations, the expression system or the type of cells. Our findings indicate that the α-synuclein-fatty acid interaction can be a critical determinant of the conformation and fate of α-synuclein in the cell interior and, as such, cPLA2 inhibitors could serve to alleviate the intracellular, potentially pathological, α-synuclein burden.

Synthesis of benzoxazole-based vorinostat analogs and their antiproliferative activity.

Hydroxamic acid derivatives constitute an interesting novel class of antitumor agents. Three of them, including vorinostat, are approved drugs for the treatment of malignancies, while several others are currently under clinical trials. In this work, we present new vorinostat analogs containing the benzoxazole ring as the cap group and various linkers. The benzoxazole-based analogs were synthesized starting either from 2-aminobenzoxazole, through conventional coupling, or from benzoxazole, through a metal-free oxidative amination. All the synthesized compounds were evaluated for their antiproliferative activity on three diverse human cancer cell lines (A549, Caco-2 and SF268), in comparison to vorinostat. Compound 12 (GK601), carrying a benzoxazole ring replacement for the phenyl ring of vorinostat, was the most potent inhibitor of the growth of three cell lines (IC50 1.2-2.1 µΜ), similar in potency to vorinostat. Compound 12 also inhibited human HDAC1, HDAC2 and HDAC6 like vorinostat. This new analog also showed antiproliferative activity against two colon cancer cell lines genetically resembling pseudomyxoma peritonei (PMP), namely HCT116 GNAS R201C/+ and LS174T (IC50 0.6 and 1.4 µΜ, respectively) with potency comparable to vorinostat (IC50 1.1 and 2.1 µΜ, respectively).

Nitro Fatty Acids (NO2-FAs): An Emerging Class of Bioactive Fatty Acids.

Unsaturated nitro fatty acids (NO2-FAs) constitute a category of molecules that may be formed endogenously by the reaction of unsaturated fatty acids (UFAs) with secondary species of nitrogen monoxide and nitrite anions. The warhead of NO2-FAs is a nitroalkene moiety, which is a potent Michael acceptor and can undergo nucleophilic attack from thiol groups of biologically relevant proteins, showcasing the value of these molecules regarding their therapeutic potential against many diseases. In general, NO2-FAs inhibit nuclear factorκ-B (NF-κB), and simultaneously they activate nuclear factor (erythroid derived)-like 2 (Nrf2), which activates an antioxidant signaling pathway. NO2-FAs can be synthesized not only endogenously in the organism, but in a synthetic laboratory as well, either by a step-by-step synthesis or by a direct nitration of UFAs. The step-by-step synthesis requires specific precursor compounds and is in position to afford the desired NO2-FAs with a certain position of the nitro group. On the contrary, the direct nitration of UFAs is not a selective methodology; thus, it affords a mixture of all possible nitro isomers.

Discovery of a stable tripeptide targeting the N-domain of CRF1 receptor.

The corticotropin-releasing factor (CRF) and its CRF1 receptor (CRF1R) play a central role in the maintenance of homeostasis. Malfunctioning of the CRF/CRF1R unit is associated with several disorders, such as anxiety and depression. Non-peptide CRF1R-selective antagonists have been shown to exert anxiolytic and antidepressant effects on experimental animals. However, none of them is in clinical use today because of several side effects, thus demonstrating the need for the development of other more suitable CRF1R antagonists. In an effort to develop novel CRF1R antagonists we designed, synthesized and chemically characterized two tripeptide analogues of CRF, namely (R)-LMI and (S)-LMI, having their Leu either in R (or D) or in S (or L) configuration, respectively. Their design was based on the crystal structure of the N-extracellular domain (N-domain) of CRF1R/CRF complex, using a relevant array of computational methods. Experimental evaluation of the stability of synthetic peptides in human plasma has revealed that (R)-LMI is proteolytically more stable than (S)-LMI. Based on this finding, (R)-LMI was selected for pharmacological characterization. We have found that (R)-LMI is a CRF antagonist, inhibiting (1) the CRF-stimulated accumulation of cAMP in HEK 293 cells expressing the CRF1R, (2) the production of interleukins by adipocytes and (3) the proliferation rate of RAW 264.7 cells. (R)-LMI likely blocked agonist actions by interacting with the N-domain of CRF1R as suggested by data using a constitutively active chimera of CRF1R. We propose that (R)-LMI can be used as an optimal lead compound in the rational design of novel CRF antagonists.

Synthesis of novel 2-pyrrolidinone and pyrrolidine derivatives and study of their inhibitory activity against autotaxin enzyme.

Autotaxin (ATX), a glycoprotein (~125 kDa) isolated as an autocrine motility factor from melanoma cells, belongs to a seven-membered family of ectonucleotide pyrophosphatase/phosphodiesterase (ENPP), and exhibits lysophospholipase D activity. ATX is responsible for the hydrolysis of lysophosphatidylcholine (LPC) to produce the bioactive lipid lysophosphatidic acid (LPA), which is upregulated in a variety of pathological inflammatory conditions, including fibrosis, cancer, liver toxicity and thrombosis. Given its role in human disease, the ATX-LPA axis is an interesting target for therapy, and the development of novel potent ATX inhibitors is of great importance. In the present work a novel class of ATX inhibitors, optically active derivatives of 2-pyrrolidinone and pyrrolidine heterocycles were synthesized. Some of them exhibited interesting in vitro activity, namely the hydroxamic acid 16 (IC50 700 nM) and the carboxylic acid 40b (IC50 800 nM), while the boronic acid derivatives 3k (IC50 50 nM), 3l (IC50 120 nM), 3 m (IC50 180 nM) and 21 (IC50 35 nM) were found to be potent inhibitors of ATX.

Development of a Liquid Chromatography-High Resolution Mass Spectrometry Method for the Determination of Free Fatty Acids in Milk.

The determination of free fatty acids (FFAs) in milk is of importance for quality control, legislative purposes, authentication and product development. We present herein a liquid chromatography-high resolution mass spectrometry method for the direct determination of FFAs in milk. The method involves mild sample preparation, avoids time-consuming derivatization and allows the direct quantification of twenty-two FFAs in a 10-min single run. It was validated and applied in thirteen cow milk and seven goat milk samples. Saturated fatty acids C16:0, C18:0 and unsaturated C18:1 (n-9) were found to be the major components of milk FFAs at concentrations of 33.1 ± 8.2 µg/mL, 16.5 ± 5.3 µg/mL and 14.8 ± 3.8 µg/mL, respectively, in cow milk and at concentrations of 22.8 ± 1.8 µg/mL, 12.7 ± 2.8 µg/mL and 13.3 ± 0.3 µg/mL, respectively, in goat milk. Other saturated and unsaturated FFAs were found in significantly lower quantities. Saturated fatty acids C6:0, C8:0 and C10:0 were found in higher quantities in goat milk than in cow milk. The levels of the important (for human health) odd-chain FFAs C15:0 and C17:0 were estimated in cow and goat milk.

A Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS) Method for the Determination of Free Hydroxy Fatty Acids in Cow and Goat Milk.

A liquid chromatography-high resolution mass spectrometry (LC-HRMS) method for the direct determination of various saturated hydroxy fatty acids (HFAs) in milk was developed for the first time. The method involves mild sample preparation conditions, avoids time-consuming derivatization procedures, and permits the simultaneous determination of 19 free HFAs in a single 10-min run. This method was validated and applied in 17 cow milk and 12 goat milk samples. This work revealed the existence of various previously unrecognized hydroxylated positional isomers of palmitic acid and stearic acid in both cow and goat milk, expanding our knowledge on the lipidome of milk. The most abundant free HFAs in cow milk were proven to be 7-hydroxystearic acid (7HSA) and 10-hydroxystearic acid (10HSA) (mean content values of 175.1 ± 3.4 µg/mL and 72.4 ± 6.1 µg/mL in fresh milk, respectively). The contents of 7HSA in cow milk seem to be substantially higher than those in goat milk.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes-7.

Breakthroughs in Medicinal Chemistry [...].

Enantioselective Organocatalysis-Based Synthesis of 3-Hydroxy Fatty Acids and Fatty γ-Lactones.

3-Hydroxy fatty acids have attracted the interest of researchers, since some of them may interact with free fatty acid receptors more effectively than their non-hydroxylated counterparts and their determination in plasma provides diagnostic information regarding mitochondrial deficiency. We present here the development of a convenient and general methodology for the asymmetric synthesis of 3-hydroxy fatty acids. The enantioselective organocatalytic synthesis of terminal epoxides, starting from long chain aldehydes, is the key-step of our methodology, followed by ring opening with vinylmagnesium bromide. Ozonolysis and subsequent oxidation leads to the target products. MacMillan's third generation imidazolidinone organocatalyst has been employed for the epoxide formation, ensuring products in high enantiomeric purity. Furthermore, a route for the incorporation of deuterium on the carbon atom carrying the hydroxy group was developed allowing the synthesis of deuterated derivatives, which may be useful in biological studies and in mass spectrometry studies. In addition, the synthesis of fatty γ-lactones, corresponding to 4-hydroxy fatty acids, was also explored.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes-5.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes is a series of Editorials which is published on a biannual basis by the Editorial Board of the Medicinal Chemistry section of the journal Molecules [...].

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes-6.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes is a series of Editorials that is published on a biannual basis by the Editorial Board of the Medicinal Chemistry section of the journal Molecules [...].

Small Peptides Able to Suppress Prostaglandin E2 Generation in Renal Mesangial Cells.

Peptide drug discovery may play a key role in the identification of novel medicinal agents. Here, we present the development of novel small peptides able to suppress the production of PGE2 in mesangial cells. The new compounds were generated by structural alterations applied on GK115, a novel inhibitor of secreted phospholipase A2, which has been previously shown to reduce PGE2 synthesis in rat renal mesangial cells. Among the synthesized compounds, the tripeptide derivative 11 exhibited a nice dose-dependent suppression of PGE2 production, similar to that observed for GK115.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes⁻4.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes is a series of Editorials, which is published on a biannual basis by the Editorial Board of the Medicinal Chemistry section of the journal Molecules. [...].

Progesterone-induced Acrosome Exocytosis Requires Sequential Involvement of Calcium-independent Phospholipase A2ß (iPLA2ß) and Group X Secreted Phospholipase A2 (sPLA2).

Phospholipase A2 (PLA2) activity has been shown to be involved in the sperm acrosome reaction (AR), but the molecular identity of PLA2 isoforms has remained elusive. Here, we have tested the role of two intracellular (iPLA2ß and cytosolic PLA2α) and one secreted (group X) PLA2s in spontaneous and progesterone (P4)-induced AR by using a set of specific inhibitors and knock-out mice. iPLA2ß is critical for spontaneous AR, whereas both iPLA2ß and group X secreted PLA2 are involved in P4-induced AR. Cytosolic PLA2α is dispensable in both types of AR. P4-induced AR spreads over 30 min in the mouse, and kinetic analyses suggest the presence of different sperm subpopulations, using distinct PLA2 pathways to achieve AR. At low P4 concentration (2 µm), sperm undergoing early AR (0-5 min post-P4) rely on iPLA2ß, whereas sperm undergoing late AR (20-30 min post-P4) rely on group X secreted PLA2. Moreover, the role of PLA2s in AR depends on P4 concentration, with the PLA2s being key actors at low physiological P4 concentrations (≤2 µm) but not at higher P4 concentrations (~10 µm).

2-Oxoamides based on dipeptides as selective calcium-independent phospholipase A2 inhibitors.

Calcium-independent phospholipase A2 (GVIA iPLA2) has recently attracted interest as a medicinal target. The number of known GVIA iPLA2 inhibitors is limited to a handful of synthetic compounds (bromoenol lactone and polyfluoroketones). To expand the chemical diversity, a variety of 2-oxoamides based on dipeptides and ether dipeptides were synthesized and studied for their in vitro inhibitory activity on human GVIA iPLA2 and their selectivity over the other major intracellular GIVA cPLA2 and the secreted GV sPLA2. Structure-activity relationship studies revealed the first 2-oxoamide derivative (GK317), which presents potent inhibition of GVIA iPLA2 (XI(50) value of 0.007) and at the same time significant selectivity over GIVA cPLA2 and GV sPLA2.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes-2.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes is a series of Editorials, which are published on a biannual basis by the Editorial Board of the Medicinal Chemistry section of the journal Molecules [...].

Development of a potent 2-oxoamide inhibitor of secreted phospholipase A2 guided by molecular docking calculations and molecular dynamics simulations.

Inhibition of group IIA secreted phospholipase A2 (GIIA sPLA2) has been an important objective for medicinal chemists. We have previously shown that inhibitors incorporating the 2-oxoamide functionality may inhibit human and mouse GIIA sPLA2s. Herein, the development of new potent inhibitors by molecular docking calculations using the structure of the known inhibitor 7 as scaffold, are described. Synthesis and biological evaluation of the new compounds revealed that the long chain 2-oxoamide based on (S)-valine GK241 led to improved activity (IC50=143 nM and 68 nM against human and mouse GIIA sPLA2, respectively). In addition, molecular dynamics simulations were employed to shed light on GK241 potent and selective inhibitory activity.