Benzoxazolone Carboxamides as Potent Acid Ceramidase Inhibitors: Synthesis and Structure–Activity Relationship (SAR) Studies

: Ceramides are lipid-derived intracellular messengers involved in the control of senescence, in ﬂ ammation, and apoptosis. The cysteine amidase, acid ceramidase (AC), hydrolyzes these substances into sphingosine and fatty acid and, by doing so, regulates their signaling activity. AC inhibitors may be useful in the treatment of pathological conditions, such as cancer, in which ceramide levels are abnormally reduced. Here, we present a systematic SAR investigation of the benzoxazolone carboxamides, a recently described class of AC inhibitors that display high potency and systemic activity in mice. We examined a diverse series of substitutions on both benzoxazolone ring and carboxamide side chain. Several modi ﬁ cations enhanced potency and stability, and one key compound with a balanced activity − stability pro ﬁ le ( 14 ) was found to inhibit AC activity in mouse lungs and cerebral cortex after systemic administration. The results expand our arsenal of AC inhibitors, thereby facilitating the use of these compounds as pharmacological tools and their potential development as drug leads.


■ INTRODUCTION
Acid ceramidase (AC) is a cysteine amidase involved in the metabolism of ceramides, bioactive lipid molecules that belong to the class of sphingolipids. 1 Sphingolipids act as cellular messengers throughout the body and are involved in the survival, growth, and differentiation of cells, 2 as well as in pathophysiological process such as inflammation and neuropathic pain. 3AC plays a pivotal role in balancing sphingolipid-mediated signaling. 4he enzyme is mainly, albeit not uniquely, located in lysosomes, 5 where it cleaves the amide bond of ceramides producing the aliphatic amino alcohol sphingosine along with fatty acid (typically 14−26 carbon atoms in length) (Figure 1).6c,7 Interestingly, ceramide concentrations increase in cells that are stressed with chemotherapeutic agents, DNA damage, and ionizing radiation, 7f through stimulation of de novo ceramide biosynthesis, hydrolysis of sphingomyelin, or the salvage pathway; 1a moreover, the cytotoxic effects of certain anticancer drugs partly depend on de novo ceramide biosynthesis. 8AC is overexpressed in several cancer types, 9 and in prostate cancer this up-regulation renders cells more resistant to chemotherapy and radiotherapy, while genetic or pharmacological AC inhibition restores sensitivity to therapy in vivo. 10Thus, modulating the ceramide/sphingosine 1phosphate axis by inhibiting AC could provide a new strategy for future therapeutics against cancer and, possibly, other pathologies in which ceramide metabolism is dysregulated.To test this hypothesis, several AC inhibitors have been developed over the past decades. 11e have recently disclosed a small set of benzoxazolone carboxamides as the first example of systemically active inhibitors of intracellular AC activity. 12We demonstrated that these molecules covalently inhibit AC through S-acylation of its catalytic nucleophile, Cys-143, with the benzoxazolone ring acting as leaving group.Preliminary structure−activity relationship (SAR) studies showed that a secondary carboxamide moiety is mandatory for activity, as in the initial hit compound 1 (h-AC IC 50 = 64 nM) (Figure 2), and that introducing a bromine atom at position 6 on the heterocyclic scaffold leads to a 2-fold increase in inhibitory potency (2, IC 50 = 31 nM), diminishing at the same time chemical and metabolic stability in aqueous buffer and mouse plasma.Also, we observed that replacing bromine with a p-fluorophenyl group, as in 6-(4-fluorophenyl)-2-oxo-N-(4-phenylbutyl)-1,3-benzoxazole-3-carboxamide (3, ARN14974) 12 allows for balancing potency (IC 50 = 79 nM) with enhanced chemical and metabolic stability (Figure 2).We found that compound 3 inhibits AC in intact cells and in vivo, causing a substantial reduction in AC activity in multiple organs and resulting in expected changes of ceramide and sphingosine levels.
In the present study we expanded our initial SAR study around compound 1 with the objective of demonstrating whether the benzoxazolone carboxamide scaffold is generally capable of providing potent AC inhibitors.We synthesized a series of benzoxazolone carboxamides to explore the roles of both position and stereoelectronic properties of substituents on the  heterocyclic scaffold, as well as the effect of side chain modifications on AC inhibition (Figure 2).Finally, we tested selected derivatives for their stability in aqueous buffer and demonstrated in vivo AC inhibitory activity of the optimized compound, 6-chloro-2-oxo-N-(4-phenylbutyl)-1,3-benzoxazole-3-carboxamide (14).

■ CHEMISTRY
A series of benzoxazolone carboxamide derivatives (4−36) bearing different substituents on the bicyclic ring system were synthesized, as outlined in Schemes 1−5.In analogy to hit compound 1, we initially coupled substituted benzoxazolones with the commercial 4-phenylbutyl isocyanate in the presence of Journal of Medicinal Chemistry 4-dimethylaminopyridine (DMAP), under basic conditions (method A). 13 First, we prepared a set of derivatives (4−19)  bearing groups with different stereoelectronic properties on the heterocyclic ring (Scheme 1).Coupling reactions proceeded smoothly to give the final carboxamides 4−19 in good yield, with the exception of compounds 4 and 7, for which no or low conversion was observed, seemingly due to the substituent at position 4 leading to chemical instability.In most cases, the starting benzoxazolone scaffolds were commercially available (37b, 37e,f, 37h,k); alternatively the properly substituted heterocycles (37a, 37c,d, 37g, 37l−p) were obtained from the corresponding 2-aminophenols by intramolecular cyclization reaction in the presence of 1,1′-carbonyldiimidazole (CDI) (Scheme 1). 14econd, we introduced aromatic substituents on the benzoxazolone scaffold by Suzuki−Miyaura coupling reaction between the appropriate bromo heterocycles (37a−c, 38) and commercially available boronic acids (Scheme 2).Couplings at positions 5 and 6 of the benzoxazolone system were accomplished in satisfactory yields, while the reactions to get 4-and 7-phenylbenzoxazolones 39a and 39d led to a complex mixture, and the intermediates were used as crudes in the following step.N-acylation of 39a−g with 4-phenylbutyl isocyanate yielded the targeted compounds 20−26.
To further expand the series of 6-substituted derivatives, compounds 31−33 bearing electron-donating and bulky alkoxy groups were prepared as shown in Scheme 4. The benzoxazolone 42 was obtained by orthogonal protection of the commercial 6hydroxy derivative 43 (Scheme 4). 15 N-protected 6-hydroxy derivative 44, which was readily alkylated with commercial alcohols under Mitsunobu reaction conditions, using triphenylphosphine and di-tert-butyl azodicarboxylate (DBAD).DBAD was degraded under mild conditions in trifluoroactic acid (TFA), 16 affording N-protected 6-alkoxybenzoxazolones 45a−c in good yield (Scheme 4).Cleavage of the methoxyethoxymethyl (MEM) group with refluxing TFA 15  Scheme 5 shows the syntheses of benzoxazolone carboxamides 34−36 bearing a benzoyl group at either position 5 or position 6.Acylation of the benzoxazolone ring could be efficiently achieved by means of Friedel−Crafts reaction.To get compound 34, the commercial N-acetyl-2-aminophenol was treated with a mild electrophile, such as the complex AlCl 3 •DMF in the presence of benzoyl chloride to regioselectively acylate position 4 (Scheme 5A).Subsequent N-acetyl group cleavage and ring closure with CDI afforded the targeted 5-benzoyl-3H-1,3-benzoxazol-2-one 49, which was then coupled to 4-phenylbutyl isocyanate.To obtain compounds 35 and 36, the unsubstituted benzoxazolone 50 was first N-acylated with benzoyl chloride or 4-chlorobenzoyl chloride to give 51a and 51b, respectively (Scheme 5B).Heating in the presence of AlCl 3 promoted the migration of acyl group from the nitrogen to the carbon atom at position 6 (52a,b), according to a "Fries-like" rearrangement mechanism. 17Final Nacylation of nitrogen N3 with 4-phenylbutyl isocyanate led to the targeted compounds.
Finally, a series of unsubstituted benzoxazolone derivatives with different side chains at the carboxamide moiety was accessed as depicted in Scheme 6. Compounds 53−66 were obtained by activating benzoxazolone 50 with triphosgene, either in pyridine (method B) (54, 62, 63, 66) or in DCM in the presence of Et 3 N (method C) (53, 55−61, 64, 65), and in situ quenching with the proper amine (67a−n) to incorporate the desired side chains (Scheme 6).Noncommercial amines (67a−j) were synthesized through a two-step sequence starting from alcohols 68a−i and bromide 69 under Mitsunobu and Gabriel reaction conditions, respectively (Scheme 7).Hydrazine-mediated cleavage of phthalimide derivatives 70a−j led to the desired amines as hydrochloride salts.Noncommercial alcohols 68a−e were readily obtained by reduction of the corresponding ester (71a) or acids (71b−e).

■ RESULTS AND DISCUSSION
We recently disclosed benzoxazolone carboxamides as the first class of potent and systemically active inhibitors of intracellular AC. 12 We demonstrated that these compounds covalently inhibit AC and identified derivative 3 as the first chemical probe that may be used to study the impact of AC inhibition in vivo (Figure 2).A preliminary SAR study around hit compound 1 revealed that a secondary carboxamide moiety is mandatory for activity, and substitution at position 6 of the benzoxazolone ring allows for modulation of the inhibitory potency against AC.These results prompted us to expand the class of benzoxazolone carboxamides by systematically investigating the effects of different substituents on the heterocyclic scaffold as well as of modifications of the side chain.The new compounds were tested for their ability to inhibit the hydrolysis of N-[(1S,2R)-2hydroxy-1-(hydroxymethyl)-4-(2-oxochromen-7-yl)oxybutyl]dodecanamide by recombinant human AC (h-AC) in a fluorescence-based assay. 18o probe for stereoelectronic effects on the benzoxazolone system, we initially monosubstituted 1 with bromine or methyl groups at position 4, 5, 6, or 7 (Table 1).As previously observed with the 6-bromo derivative 2 (IC 50 = 31 nM), introduction of bromine at either position 5 or 7 led to a 2-to 4-fold increase in potency relative to 1 (5, IC 50 = 22 nM, and 6, IC 50 = 18 nM).Bromine introduction at position 4 yielded the unstable derivative 4, and the same result was obtained when a methyl group was introduced at the same position (7).As for the small set of methyl-substituted derivatives, with the exception of compound 10 bearing a methyl at position 7 and having an IC 50 of 23 nM, the introduction of this group led to a decrease in potency when the methyl was placed in position 5 (8, IC 50 = 117 nM) or to an equipotent compound, compared to 1, when the Scheme 7. Synthesis of Amines 67a−j a a Yields are not reported when compounds were used as crude in the following step.Alcohols 68f−i and amines 67k−n were commercially available.methyl was placed in position 6 (9, IC 50 = 66 nM).Next, we expanded the set of substituted analogs at positions 5 and 6 investigating compounds 11−19, which were 2-to 20-fold more potent than 1 (Table 1).The 5-fluoro derivative 11 (IC 50 = 12 nM) turned out to be ∼3-fold more potent than the corresponding 6-substituted analog 12 (IC 50 = 31 nM).The same trend in potency associated with halide introduction at either position 5 or 6 was observed for the chloro-substituted compounds 13 and 14 (and for the bromine-substituted 5 and 2).Replacement of halides with strong electron-withdrawing groups such as trifluoromethyl and nitro groups diminished the difference in potency between 5-and 6-substituted derivatives (15−18).Of particular interest were the results obtained with 5nitrobenzoxazolone carboxamide 17 and the corresponding 6nitro analog 18, which represent the first single-digit nanomolar compounds in this class, both inhibiting AC with an IC 50 value of 3 nM.Finally, we explored whether incorporating simultaneously two favorable substitutions would provide additive effects.We observed that the disubstituted compound 19 was potent (IC 50 = 18 nM) but not significantly more so than the related monosubstituted analogs 13 and 14 (Table 1).
As a continuation of the SAR study around the benzoxazolone system, we prepared a small series of derivatives bearing a phenyl ring (Table 2).First, we systematically explored the introduction of this moiety at positions 4, 5, 6, and 7. Interestingly, stability issues did not prevent isolation and testing of the 4-phenyl derivative 20, which turned out to be 75-fold more potent than 1 (IC 50 = 0.8 nM).Derivatives 21−23 bearing a phenyl ring at positions 5, 6, and 7, respectively, were approximately as potent as 1.Next, we focused on positions 5 and 6 and prepared a small series of aryl-substituted derivatives (24−36).Overall, decorat-ing the phenyl ring with fluorine or methoxy group in the para position (3, 24 and 25, 26) did not improve potency over the unsubstituted benzoxazolone derivative 1.However, replacement of the phenyl with aryl ketones (34−36) led to 2-to 5-fold increases in potency relative to 1, with compound 36 (IC 50 = 14 nM) being the most potent within this small series.Finally, introduction of an alkylic or alkenylic spacer between the benzoxazolone system and the phenyl ring as well as the replacement of the phenyl with a cyclohexyl led to a loss in potency, with compounds 27−30 (Scheme 3) showing no inhibitory activity against AC at the concentrations tested (50 and 500 nM).Similarly, compounds 31−33 (Scheme 4) bearing various alkoxy groups at position 6 were inactive.
We next examined the role of the side chain by preparing a series of unsubstituted benzoxazolone carboxamides.First, we evaluated the length of the carbon linker between the benzoxazolone and the phenyl ring of 1. Compounds 53−56, in which the spacer was progressively increased from two to six methylene units, were tested for their inhibitory activity (Table 3).The short linker with two methylene units led to a 2-fold decrease in potency (53, IC 50 = 121 nM) compared to 1, while compounds 54−56, which contain a three-, five-, or six-carbon atom linker, respectively, turned out to be as potent as 1.Replacement of one methylene unit of the four-carbon atom chain of 1 with a heteroatom (62−64) was detrimental for activity, with the exception of the thioether derivative 63, which was equipotent to 1. Next, to evaluate the role of the phenyl ring, we replaced it with a naphthyl (57) or thiophene (65) group, observing an increase in potency with the latter derivative (65, IC 50 = 37 nM).Introduction of substituents with different electronic properties in the para position of the phenyl ring was generally well tolerated, as shown by compounds 59−61, with the exception of derivative 58 (IC 50 = 312 nM), which turned out to be 5-fold less potent than 1.Interestingly, the most potent compound of this series showed the same side chain length as 1 but with the phenyl ring situated one carbon atom from the N3carboxamide group (66, IC 50 = 19 nM).
Previously, we reported that introducing bromine in position 6 (2) destabilizes compounds and leads to lower half-life in PBS  and blood plasma compared to 1 but that having a p-fluorophenyl in position 6 (3) enhanced chemical and metabolic stability dramatically.Conversely, stability under standard AC assay conditions (pH 4.5) was not affected by these substitutions. 12In order to gain a more comprehensive understanding of the structure−stability relationship of benzoxazolone carboxamides, compounds 14, 19−26, and 35,36 were tested for stability in aqueous buffer at physiological pH (Table 4).Representative compounds (14, 17, 18, 21, 35, 36) were also evaluated for their stability at pH 4.5 (Table S1, Supporting Information).At acidic pH, all compounds were stable, as previously observed with derivatives 1−3.The analysis at physiological pH showed that, in contrast to bromine, chlorine in position 6 (14) or positions 5 and 6 ( 19) did not induce instability relative to the unsubstituted and interestingly its close analog 36 was even more stable with a half-life 6-fold higher than 1 (Table 4).Overall, these results demonstrate that stability properties are not simply explained by the electronegativity of the substituents on the benzoxazolone ring and that increased activity is not necessarily linked with decreased stability.Indeed, we see that it is possible to increase potency without decreasing stability, as exemplified by compounds 14 and 19, and that it is even possible to enhance both potency and stability relative to 1 as seen for compounds 35 and 36.However, the most potent compound in this series, compound 20 (IC 50 = 0.8 nM, Table 2) also showed the lowest half-life, providing a case in which activity and stability are seemingly related.
To test whether the explored structural modifications of the benzoxazolone carboxamide scaffold could also provide novel systemically active compounds, we selected derivative 14 for further pharmacological studies in vivo, based on its balanced profile in terms of potency, stability, solubility, and druglikeness.Indeed, compound 14 shows an improved potency compared to 3 and an adequate solubility in the vehicle used for systemic administration.In this regard, other slightly more potent and stable derivatives of this series, such as compounds 35 and 36, were found to be poorly soluble and thus difficult to handle in in vivo studies.As additional criteria of selection, we considered the druglikeness of 14 in comparison with other considerably more potent compounds, such as the single-digit nanomolar inhibitors 17 and 18.The nitro-substituted benzoxazolone ring makes these derivatives important for SAR purposes but not promising as candidates for further development, due to the potential in vivo toxicity of aromatic nitro groups.
Compound 14 was injected in mice at the dose of 10 mg kg −1 (ip), and AC activity was evaluated at different time points in lysosomal fractions prepared from lung tissue and cerebral cortex.We selected the lungs because of the high basal AC activity in this tissue, and the cerebral cortex to evaluate the ability of 14 to reach the brain.As shown in Figure 3, the compound significantly inhibited AC activity in both compartments.The effect was long lasting, as AC inhibition was still observed 24 h after administration, although a slight recovery in activity was seen at this time point (Figure 3A and 3C).In the lungs, AC inhibition was accompanied by an increase in the levels of ceramide and dihydroceramide (namely, d18:1/16:0 and d18:0/16:0) for up to 6 h; sphingosine and sphingosine 1phosphate were also decreased at 3 h (Figure 3B).No statistically significant changes in sphingolipid levels were observed in the cerebral cortex (Figure 3D), presumably owing to the relative low level of AC inhibition achieved in that brain region.The results indicate that 14 engages its intended target in two relevant tissues, with results that are comparable to those previously obtained with compound 3 under the same experimental conditions. 12

■ CONCLUSIONS
The present study describes a systematic SAR investigation of a recently disclosed class of AC inhibitors that features the benzoxazolone carboxamide scaffold. 12We show that this scaffold is able to provide stable systemically active AC inhibitors and may thus represent a good starting point for further discovery.We present various synthetic approaches to obtain diversified analogs in high yields and with great feasibility.We show that electron-withdrawing groups in positions 5−7 of the benzoxazolone scaffold (2, 5, 6, 10−19) lead to enhanced inhibitory activity toward AC.This is consistent with the mechanism of action of these agents, as electron-withdrawing groups are likely to make the carboxamide carbonyl more prone to nucleophilic attack by AC's active site cysteine.Introducing a phenyl group at position 4 gave a highly potent but very unstable compound (20), which correlates with the chemical instability seen with other molecules substituted in the same position (4 and 7).Additionally, we investigated a range of aromatic substitutions on positions 5−7 of the benzoxazolone scaffold (21−26), which all provide stable compounds but do not improve activity toward AC.Also, we demonstrated that long and bulky aliphatic groups are not favorable for inhibitory activity, as seen with compounds 27−30 and 31−33.Instead, we found that substitutions with benzoyl (34, 35) or 4chlorobenzoyl (36) groups combine good potency and high stability: the most favorable of these derivatives, 36, shows a 5-to 6-fold improvement in AC inhibition relative to 1 and 3 and a 6fold improvement in stability relative to 1. Finally, we addressed the role of the carboxamide side chain and demonstrated that the inhibitory potency of 1 could be improved 2-to 3-fold by incorporating the phenyl group within the linker (66) or replacing it with thiophene (65).On the basis of potency, stability, and adequate solubility, we chose to investigate compound 14 for in vivo activity.We show that following systemic administration in mice, this compound inhibits AC in peripheral tissues as well as in the brain, leading to the expected variations in the sphingolipid profile.This provides essential evidence that AC inhibition can be successfully obtained in live animals using potent and reasonably stable benzoxazolone carboxamides.Compound 14 might be used as a tool to unravel the biological role of AC and define the potential value of this enzyme as a therapeutic target.
■ EXPERIMENTAL SECTION Chemistry.General.All commercial available reagents and solvents were used as purchased from vendors without further purification.Dry solvents (pyridine, DCM) were purchased from Sigma-Aldrich.Automated column chromatography purifications were done using a Teledyne ISCO apparatus (CombiFlash Rf) with prepacked silica gel columns of different sizes (from 4 g up to 40 g).Mixtures of increasing polarity of cyclohexane and ethyl acetate (EtOAc) were used as eluents (unless otherwise stated).Microwave heating was performed using Explorer-48 positions instrument (CEM).Hydrogenation reactions were performed using H-Cube continuous hydrogenation equipment (SS-reaction line version), employing disposable catalyst cartridges (CatCart) preloaded with the required heterogeneous catalyst.NMR experiments were run on a Bruker Avance III 400 system (400.13 MHz for 1 H and 100.62 MHz for 13 C), equipped with a BBI probe and Zgradients.Spectra were acquired at 300 K, using deuterated dimethyl sulfoxide (DMSO-d 6 ) or deuterated chloroform (CDCl 3 ) as solvents.Chemical shifts for 1 H and 13 C spectra were recorded in parts per million using the residual nondeuterated solvent as the internal standard (for CDCl 3 , 7.26 ppm, 1 H, and 77.16 ppm, 13 C; for DMSO-d 6 , 2.50 ppm, 1 H, and 39.52 ppm, 13 C).UPLC−MS analyses were run on a Waters ACQUITY UPLC−MS system consisting of a SQD (single quadrupole detector) mass spectrometer equipped with an electrospray ionization interface and a photodiode array detector.PDA range was 210−400 nm.Analyses were performed on an ACQUITY UPLC HSS T3 C 18 column (50 mm × 2.1 mm i.d., particle size 1.8 μm) with a VanGuard HSS T3 C 18 precolumn (5 mm × 2.1 mm i.d., particle size 1.8 μm).Mobile phase was either 10 mM NH 4 OAc in H 2 O at pH 5 adjusted with AcOH (A) or 10 mM NH 4 OAc in MeCN−H 2 O (95:5) at pH 5 (B).Electrospray ionization in positive and negative mode was applied.All final compounds showed ≥95% purity by NMR ( 1 H, 13 C, 1 H− 1 H COSY, 1 H− 13 C HSQC) and UPLC−MS (UV).DMSO stock solutions of final compounds (10 mM) used for biological tests were evaluated prior to tests (NMR, LC−MS), and concentration was assessed by quantitative 1 H NMR.
General Procedure for the Synthesis of Final Benzoxazolone N-Carboxamides 4−36 via Method A (Schemes 1−5 and Tables 1 and 2).The properly substituted 3H-1,3-benzoxazol-2-one (1.0 equiv) was dissolved in dry pyridine (6 mL per mmol benzoxazol-2one).DMAP (1.1 equiv) was added and the reaction mixture stirred under nitrogen atmosphere at rt for 30 min.4-Phenylbutyl isocyanate (1.1 equiv) was added and the resulting mixture was stirred for 15 h.The solvent was removed under reduced pressure, and the compound was purified by silica gel column chromatography using the Teledyne ISCO apparatus (cyclohexane/EtOAc).
Fluorescence-Based in Vitro Assay.Compounds were assessed for their ability to inhibit hydrolysis of the fluorogenic substrate, N-[(1S,2R)-2-hydroxy-1-(hydroxymethyl)-4-(2-oxochromen-7-yl)oxybutyl]dodecanamide, which is converted to umbelliferone by AC in the fluorescence-based in vitro assay, as previously described. 12,18ysosomal lysate, enriched with AC, was prepared from Hek293 cells stably expressing human AC and preincubated with test compounds and a positive control (diluted 20× from DMSO stock solutions at different concentrations) for 10 min.Then, the fluorogenic substrate (diluted 40× from EtOH stock solution, final concentration 5 μM) was added and the mixture was incubated for 3 h at 37 °C, stopped with MeOH, and treated with NaIO 4 (fresh solution in 100 mM glycine/NaOH buffer pH 10.6) followed by a 2 h incubation at 37 °C in the dark.Fluorescence intensities were measured (excitation/emission: 355/460 nm) and plotted as a function of compound concentrations.IC 50 values were calculated by nonlinear regression analysis using GraphPad Prism 5 (GraphPad Software Inc., CA, USA) applying a standard slope curve fitting.
PBS Stability Assay. 12Compounds were incubated at 10 μM in phosphate-buffered saline (pH 7.4; 1% DMSO) at 37 °C under shaking.Compounds were sampled at various time points and analyzed on a Xevo triple-quad UPLC system using a BEH C18 reversed phase column and a linear gradient of MeCN in water.Stability was evaluated from the corresponding MRM (multiple reaction monitoring) peak areas plotted versus time.The corresponding decay profile was fitted with Prism to derive the corresponding half-life values.
Animals and Treatments.Male C57BL/6 mice (20−35 g, Charles River) were group-housed at rt on a 12 h light/dark cycle.Water and standard chow pellets were freely available.Drugs were dissolved in 15% polyethylene glycol, 15% Tween-80, and 70% saline (injection volume, 10 mL/kg; ip).Animals were sacrificed 30 min, 3 h, 6 h, 12 h, 16 h, and 24 h after drug administration; tissues were collected, frozen in liquid nitrogen, and stored at −80 °C.All procedures were performed in accordance with the Italian regulations on the protection of animals used for experimental and other scientific purposes (D.M. 116192) and with European Economic Community regulations (O.J. of E.C. L 358/1 12/ 18/1986).
AC Activity in Lungs and Cerebral Cortex.AC activity in lung and cerebral cortex lysosomal extracts was measured by LC−MS as previously described. 19Briefly, tissues (10−20 mg) were suspended in 20 mM Tris-HCl (pH 7.5) with 0.32 M sucrose, sonicated, and centrifuged at 800g for 15 min at 4 °C.Supernatants were then centrifuged at 12.000g for 30 min at 4 °C.Pellets were resuspended in PBS buffer (pH 7.4) and subjected to two freeze−thaw cycles at −80 °C.The suspension was finally centrifuged at 105.000g for 1 h at 4 °C, and protein concentration was measured in the supernatant with bicinchoninic acid based protein assay.Lysosomal preparations from tissues were diluted in assay buffer (100 mM sodium phosphate, 0.1% Nonidet P-40, 150 mM NaCl, 3 mM DTT, 100 mM sodium citrate, pH 4.5).Reactions were started by the addition of 50 μM C12-ceramide (Nu-Chek Prep, Elysian, MN) and carried on for 1 h at 37 °C.Reactions were stopped by addition of a mixture of chloroform/MeOH (2:1) containing 1 nmol of 11-lauroleic acid (NuChek Prep).The organic phases were collected, dried under nitrogen, and analyzed by UPLC− MS (Acquity, Waters) in the negative-ion mode monitoring the reaction product (lauric acid, m/z: 199) using 11-lauroleic acid as internal standard.Lipids were eluted on an Acquity UPLC BEH C18 column (50 mm length, 2.1 mm i.d., 1.7 μm pore size, Waters) at 0.5 mL min −1 for 1.5 min with a gradient of MeCN and water, both containing 0.25% acetic acid and 5 mM ammonium acetate (70−100% MeCN in 0.5 min, 100% MeCN for 0.5 min, 70% MeCN for 0.4 min).The column temperature was 40 °C.Electrospray ionization (ESI) was in the negative mode, capillary voltage was 1 kV, and cone voltage was 50 V.N 2 was used as drying gas at a flow rate of 500 L/h and at a temperature of 400 °C.The [M − H] − ion was monitored in the selected-ion monitoring mode (m/z values: lauric acid 199, 11-lauroleic acid 197.35).Calibration curves were generated with authentic lauric acid (Nu Check Prep).

compound 1 .
Aromatic substitutions in positions 5−7 enhanced stability in all cases (3, 21−26), with p-fluorophenyl in position 6 (3) being the most efficient substituent and p-methoxyphenyl in the same position (26) the least efficient one.Noticeably, incorporating a phenyl group in position 4 resulted in a very unstable compound (20), which tallies well with the chemical instability observed with other compounds (4, 7) with substitutions in the same position.Finally, compound 35 with the benzoyl group in position 6 demonstrated enhanced stability,

Table 1 .
Inhibitory Potencies (IC 50 ) of Compounds on Human AC Activity a a IC 50 values are reported as mean values of two or more determinations.nd: not determined due to low chemical stability.b IC 50 values from ref 12.

Table 2 .
Inhibitory Potencies (IC 50 ) of Compounds on Human AC Activity a 29 ± 1 36 6-CO(p-Cl-Ph) 14 ± 4 a IC 50 values are reported as mean values of two or more determinations.b IC 50 values from ref 12.

Table 3 .
Inhibitory Potencies (IC 50 ) of Compounds on Human AC Activity a a IC 50 values are reported as mean values of two or more determinations.b IC 50 values from ref 12. c Tested at 5 μM.