Synthesis of novel nitric oxide (NO)-releasing esters of timolol

A novel class of timolol derivatives with nitric oxide (NO)-donating moieties achieved chemical stability yet under physiologically relevant conditions released timolol and NO. Hindered esters A were designed and synthesized, whose ‘triggered’ release relied on enzymatic hydrolysis of the nitrate ester in A to B, that in turn cyclized to liberate timolol.     

Acidic biphenyl derivatives: Synthesis and biological activity of a new series of potent 5-HT4 receptor antagonists

Serotonin (5-hydroxytryptamine, 5-HT) is an important signaling molecule in the central nervous system (CNS) and in non-neuronal tissues and organs. Serotonin mediates a positive chronotropic and inotropic response through 5-HT₄ receptors in the atrium and ventricle of the heart. Recent investigations have revealed increased expression of the 5-HT_4(b) isoform in cardiomyocytes of chronic arrhythmic and failing hearts, and that the use of 5-HT₄ receptor antagonists may be beneficial for treating these conditions. The 5-HT₄ receptor possesses a transmembrane (TM) binding site important for ligand affinity and recognition, as well as a capacity to accommodate bulky ligands. A new series of peripherally-acting 5-HT₄ receptor antagonists were prepared by combining the acidic biphenyl group from the class of angiotensin II receptor blockers (ARBs) with the SB207266 (piboserod) scaffold. The new compounds were pharmacologically evaluated and carboxylic acid 21 was identified as a potent and promising 5-HT₄ receptor antagonist with moderate affinity for the AT₁ receptor. The permeability of carboxylic acid 21 in a Caco-2 assay was low and the corresponding prodrug esters 23a–f were therefore prepared. The pharmacokinetics of methyl ester 20 and n-butyl ester 23c were evaluated in a rat model, revealing incomplete metabolism to carboxylic acid 21. However, methyl ester 20 is a potent 5-HT₄ receptor antagonist with binding affinities in the low picomolar range. Methyl ester 20 has promising oral bioavailability and pharmacokinetics and may target 5-HT₄ receptors in both CNS and peripheral organs.     

Biotransformation of p-, m-, and o-hydroxybenzoic acids by Panax ginseng hairy root cultures

The regioselective glycosylation of three isomers of hydroxybenzoic acids was observed in Panax ginseng hairy root cultures. p-Hydroxybenzoic acid (1) and m-hydroxybenzoic acid (2) were converted into their corresponding glycosides (1a and 2a) and glycosyl esters (1b and 2b) while no metabolite of o-hydroxybenzoic acid (3) was detected. A new compound, m-hydroxybenzoic acid β-d-xylopyranosyl (1 → 6)-β-d-glycopyranosyl ester (2c) was identified as a biotransformation product of 2. Further time-course studies of the biotransformation reactions showed that the glycosides were major products in the latter stage. The addition of carbohydrates or antioxidants increased glycosyl esters formation.     

Synthesis of N-hydroxycinnamoyl amide derivatives and evaluation of their anti-oxidative and anti-tyrosinase activities

Twelve N-hydroxycinnamoyl amino acid amide ethyl esters (CAES) were synthesized by using l-amino acid ethyl ester hydrochloride and corresponding cinnamic acid (ferulic acid, acetylferulic acid and caffeic acid) as raw materials in the presence of a catalytic amount of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide-hydrochloride (EDC) and 1-hydroxybenzotriene (HOBt). The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activities of CAES were evaluated. The anti-tyrosinase activities of N-feruloyl amino acid ethyl esters and the hydroxyl (OH) free radical scavenging activities of N-caffeoyl amino acid ethyl esters were also examined. DPPH free radical scavenging activity was shown in all CAES, of which N-caffeoyl amino acid ethyl esters demonstrated higher radical scavenging activity than N-feruloyl amide derivatives, and (E) -N-(caffeic acid)-l-glycinate ethyl ester (c₅) had the strongest ability to scavenge free radicals with an IC₅₀ value of 18.6 µM. The acetylferuloyl amino acid esters exhibited the highest tyrosinase inhibition activity among the tested amides.     

Dinitroglyceryl and diazen-1-ium-1,2-diolated nitric oxide donor ester prodrugs of aspirin,indomethacin and ibuprofen: Synthesis,biological evaluation and nitric oxide release studies

A new group of hybrid nitric oxide (NO) releasing anti-inflammatory (AI) ester prodrugs (NONO-NSAIDs) wherein a 1,3-dinitrooxy-2-propyl (12a–c), or O²-acetoxymethyl-1-[2-(methyl)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (14a–c), NO-donor moiety is directly attached to the carboxylic acid group of aspirin, indomethacin or ibuprofen were synthesized. NO release from the dinitrooxypropyl, or diazen-1-ium-1,2-diolate, ester prodrugs was increased substantially upon incubation in the presence of l-cysteine (12a–c) or rat serum (14a–c). The ester prodrugs (12a–c, 14a–c), which did not inhibit the COX-1 isozyme, exhibited modest inhibitory activity against the COX-2 isozyme. The NONO-NSAIDs 12a–c and 14a–c exhibited in vivo AI activity that was similar to that exhibited by the parent drug aspirin, indomethacin or ibuprofen when the same oral dose (μmol/kg) was administered. These similarities in oral potency profiles suggest these NONO-NSAIDs act as classical prodrugs that require metabolic activation by esterase-mediated hydrolysis. Hybrid NO-donor/anti-inflammatory prodrugs of this type (NONO-NSAIDs) offer a potential drug design concept targeted toward the development of anti-inflammatory drugs with reduced adverse gastrointestinal effects.     

Overexpression of sterol carrier protein-2 differentially alters hepatic cholesterol accumulation in cholesterol-fed mice

Although in vitro studies suggest a role for sterol carrier protein-2 (SCP-2) in cholesterol trafficking and metabolism, the physiological significance of these observations remains unclear. This issue was addressed by examining the response of mice overexpressing physiologically relevant levels of SCP-2 to a cholesterol-rich diet. While neither SCP-2 overexpression nor cholesterol-rich diet altered food consumption, increased weight gain, hepatic lipid, and bile acid accumulation were observed in wild-type mice fed the cholesterol-rich diet. SCP-2 overexpression further exacerbated hepatic lipid accumulation in cholesterol-fed females (cholesterol/cholesteryl esters) and males (cholesterol/cholesteryl esters and triacyglycerol). Primarily in female mice, hepatic cholesterol accumulation induced by SCP-2 overexpression was associated with increased levels of LDL-receptor, HDL-receptor scavenger receptor-B1 (SR-B1) (as well as PDZK1 and/or membrane-associated protein 17 kDa), SCP-2, liver fatty acid binding protein (L-FABP), and 3α-hydroxysteroid dehydrogenase, without alteration of other proteins involved in cholesterol uptake (caveolin), esterification (ACAT2), efflux (ATP binding cassette A-1 receptor, ABCG5/8, and apolipoprotein A1), or oxidation/transport of bile salts (cholesterol 7α-hydroxylase, sterol 27α-hydroxylase, Na⁺/taurocholate cotransporter, Oatp1a1, and Oatp1a4). The effects of SCP-2 overexpression and cholesterol-rich diet was downregulation of proteins involved in cholesterol transport (L-FABP and SR-B1), cholesterol synthesis (related to sterol regulatory element binding protein 2 and HMG-CoA reductase), and bile acid oxidation/transport (via Oapt1a1, Oatp1a4, and SCP-x). Levels of serum and hepatic bile acids were decreased in cholesterol-fed SCP-2 overexpression mice, especially in females, while the total bile acid pool was minimally affected. Taken together, these findings support an important role for SCP-2 in hepatic cholesterol homeostasis.     

Synthesis and anti-tumor evaluation of novel 25-hydroxyprotopanaxadiol analogs incorporating natural amino acids

In the current study, derivatives of 25-hydroxyprotopanaxadiol (25-OH-PPD) were prepared and their in vitro anti-tumor activities were tested on six different human tumor cell lines by standard MTT assay. The results showed that combining an ester group combined with the presence of an amino acid moiety led to a 10-fold improved anti-tumor activity. Compound 1c exhibited the best anti-tumor activity in the in vitro assays. Compounds 2c, 3c, 4c, 5c, 6c and 8b showed better anti-tumor activities compared to the parent compound 25-OH-PPD. The current results may provide useful data for researching and developing new anti-cancer agents.     

Steroidal glycosides from the marine sponge Pandaros acanthifolium

The chemical composition of the Caribbean sponge Pandaros acanthifolium was investigated and led to the isolation of seven new steroidal glycosides namely pandarosides A-D (1, 3, 4 and 6) along with the three methyl esters of pandarosides A, C, and D (2, 5 and 7). Their structures were characterized as 3β-[β-glucopyranosyl-(1→2)-β-glucopyranosyloxyuronic acid]-16-hydroxy-5α,14β-poriferast-16-ene-15,23-dione (1) and its methyl ester (2), 3β-[β-glucopyranosyloxyuronic acid]-16-hydroxy-5α,14β-poriferast-16-ene-15,23-dione (3), 3β-[β-glucopyranosyl-(1→2)-β-glucopyranosyloxyuronic acid]-16-hydroxy-5α,14β-cholest-16-ene-15,23-dione (4) and its methyl ester (5), 3β-(β-glucopyranosyloxyuronic acid)-16-hydroxy-5α,14β-cholest-16-ene-15,23-dione (6) and its methyl ester (7) on the basis of detailed spectroscopic analyses, including 2D NMR and HRESIMS studies. Pandarosides A-D and their methyl esters (1-7) are all characterized by a rare 2-hydroxycyclopentenone D-ring with a 14β configuration. The absolute configuration of the aglycon part of pandaroside A (1) was assigned by comparison between experimental and TDDFT calculated circular dichroism spectra on the more stable conformer.     

Synthesis and antitumor activity of three novel ginsenoside M1 derivatives with 3′-ester modifications

Ginsenoside M1 (M1) was considered to be the main antitumor component of ginsenoside metabolites in the body. In order to enhance its potency on antitumor effect, three novel M1 3′–ester derivatives (1c, 2c, 3c) were synthesized and evaluated. The yield of these derivatives was between 41% and 69%. Compared with M1, 2c and 3c can improve the efficacy of the inhibition on breast cancer MCF–7 and MDA–MB–231 cells, especially for MCF–7 (fold: 0.7–4.2, p < 0.0001). Further study suggested that 2c and 3c may cause cell autophagy and promote apoptosis in MCF–7 cells. The results indicated the 3′–ester modified M1 derivatives 2c and 3c possess higher abilities of inhibition growth towards triple–positive breast cancer and provided a new source for synthesis of potential anti-breast cancer drugs.     

Acyclic nucleoside phosphonates with 5-azacytosine base moiety substituted in C-6 position

Two methods for preparation of 6-substituted derivatives of anti DNA-viral agent 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine (HPMP-5-azaC) were developed: (1) ammonia mediated ring-opening reaction of diisopropyl esters of HPMP-5-azaC (4) to carbamoylguanidine derivatives followed by ring-closure reaction with orthoesters and (2) condensation reaction of 6-substituted 5-azacytosines with diisopropyl (1S)-[2-hydroxy-1-tosyloxymethyl)ethoxy]methylphosphonate (15). Deprotection of diisopropyl esters to free phosphonic acids was performed with bromotrimethylsilane in acetonitrile followed by hydrolysis. In contrast to parent compound HPMP-5-azaC, a substantial decrease of antiviral activity in case of 6-substituted analogues occurred. Surprisingly, N-3 isomer of 6-methyl-HPMP-5-azaC in the form of isopropyl ester revealed activity against RNA viruses (Sindbis virus).     

Synthesis and in vivo influenza virus-inhibitory effect of ester prodrug of 4-guanidino-7-O-methyl-Neu5Ac2en

A series of ester prodrugs of 7-O-methyl derivative of Zanamivir (compound 3) was synthesized and their efficacy was evaluated in an influenza infected mice model by intranasal administration. Compound 7c (CS-8958), octanoyl ester prodrug of the C-9 alcohol of compound 3, was found to be much longer-acting than Zanamivir. Furthermore, the in vivo efficacies of compounds 12a, 12b, and 12c, the linear alkyl ester prodrug of the carboxylic acid, were comparable to that exerted by compound 7c.     

Design and synthesis of novel benzimidazole derivatives as phosphodiesterase 10A inhibitors with reduced CYP1A2 inhibition

A novel class of phosphodiesterase 10A (PDE10A) inhibitors with reduced CYP1A2 inhibition were designed and synthesized starting from 2-{[(1-phenyl-1H-benzimidazol-6-yl)oxy]methyl}quinoline (1). Introduction of an isopropyl group at the 2-position and a methoxy group at the 5-position of the benzimidazole ring of lead compound 1 resulted in the identification of 2-{[(2-isopropyl-5-methoxy-1-phenyl-1H-benzimidazol-6-yl)oxy]methyl}quinoline (25b), which exhibited potent PDE10A inhibitory activity with reduced CYP1A2 inhibitory activity compared to compound 1.     

Synthesis of ethyl-(3R,5S)-dihydroxy-6-benzyloxyhexanoates via diastereo- and enantioselective microbial reduction: Cloning and expression of ketoreductase III from Acinetobacter sp. SC 13874

Previously we have demonstrated the reduction of ethyl and t-butyl diketoesters 1 to the corresponding syn-(3R,5S)-dihydroxy esters 2a by Acinetobacter sp. 13874. The syn-(3R,5S)-dihydroxy ester 2a was obtained with an enantiomeric excess (e.e.) of 99% and a diastereomeric excess (de) of 63%. In this report, we identified a gene encoding desired ketoreductase III which catalyzed the diastereoselective reduction of diketoesters 1 to syn-(3R,5S)-dihydroxy esters 2a and describe cloning and expression of ketoreductase III into Escherichia coli. Cells or extracts of recombinant E. coli efficiently reduced the diketoester 1 to the corresponding syn-(3R,5S)-dihydroxy ester 2a in 99.3% yield, 100% e.e., and 99.8% de.     

Synthesis of 2,6-di(acylamino)-2,6-dideoxy-3-O-(d-2-propanoyl-l-alanyl-d-isoglutamine)-d-glucopyranoses

Five 2,6-di(acylamino)-2,6-dideoxy-3-O-(d-2-propanoyl-l-alanyl-d-isoglutamine)-d-glucopyranoses (lipophilic, muramoyl dipeptide analogs) were synthesized from benzyl 2-(benzyloxycarbonylamino)-3-O-(d-1-carboxyethyl)-2-deoxy-5,6-O-isopropylidene-β-dglucopyranoside (1). Methanesulfonylation of 3, derived from the methyl ester of 1 by O-deisopropylidenation, gave the 6-methanesulfonate (4). (Tetrahydropyran-2-yl)ation of 4 gave benzyl 2-(benzyloxycarbonylamino)-2-deoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-6-O-(methylsulfonyl)-5-O-(tetrahydropyran-2-yl)-β-d- glucofuranoside, which was treated with sodium azide to give the corresponding 6-azido derivative (6). Condensation of benzyl 6-amino-2-(benzyloxycarbonyl-amino)-2,6-dideoxy-3-O-[d-1-(methoxycarbonyl)ethyl]-5-O-(tetrahydropyran-2-yl)-β-d-glucofuranoside, derived from 6 by reduction, with the activated esters of octanoic, hexadecanoic, and eicosanoic acid gave the corresponding 6-N-fatty acyl derivatives (8–10). Coupling of the 2-amino derivatives, obtained from compounds 8, 9, and 10 by catalytic reduction, with the activated esters of the fatty acids, gave the 2,6-(diacylamino)-2,6-dideoxy derivatives (11–15). Condensation of the acids, formed from 11–15 by de-esterification, with the benzyl ester of l-alanyl-d-isoglutamine, and subsequent hydrolysis, afforded benzyl 2,6-di(acylamino)-2,6-dideoxy-3-O-(d-2-propanoyl-l-alanyl-d-isoglutamine benzyl ester)-β-d-glucofuranosides. Hydrogenation of the dipeptide derivatives thus obtained gave the five lipophilic analogs of 6-amino-6-deoxymuramoyl dipeptide, respectively, in good yields.     

A possible biogenetic-type synthesis of 2-methylisoflavones

Two α-methylchalcones (2c and 2d), on oxidation with thallium (III) nitrate, afford the corresponding 2-methylisoflavones (4c and 4d, respectively), 4c being the natural isoflavone isolated from Glycyrrhiza glabra. This synthesis is the first of 2-methylisoflavones starting from α-methylchalcones, which could also be the precursors in Nature.     

Olive secoiridoids and semisynthetic bioisostere analogues for the control of metastatic breast cancer

(?)-Oleocanthal (1) and ligstroside aglycone (2) are common bioactive olive oil secoiridoids. Secoiridoid 1 has been previously reported as a c-MET inhibitor. Chemically, (?)-oleocanthal is the elenolic acid ester of the common olive phenolic alcohol tyrosol. Therefore, several analogues (4–13) were synthesized by esterification and carbamoylation of tyrosol using diverse phenolic naturally occurring in olive and heterocyclic acids as elenolic acid bioisosteres to assess the effect of replacing the acid moiety of (?)-oleocanthal. Their c-MET inhibitory activity as well as their antiproliferative, antimigratory, and anti-invasive activities against the highly metastatic human breast cancer cell line MDA-MB231 has been assessed. Ligstroside aglycone (2) showed the best antimigratory activity. Generally, tyrosol esters showed better activities versus carbamate analogues. Tyrosol sinapate (5) showed the best c-MET phosphorylation inhibitory activity in Z′-LYTE? kinase assay. Both 1 and 5 competitively inhibited the ATP binding into its pocket in the c-MET catalytic domain. Compound 5 showed selective activities against tumor cells without toxicity to the non-tumorigenic human breast MCF10A epithelial cell line. Tyrosol esters with a phenolic acid containing hydrogen bond donor and/or acceptor groups at the para-position have better anticancer and c-MET inhibitory activities. Olive oil secoiridoids are excellent scaffolds for the design of novel c-MET inhibitors.     

Tetrazole-based deoxyamodiaquines: Synthesis,ADME/PK profiling and pharmacological evaluation as potential antimalarial agents

A series of new deoxyamodiaquine-based compounds was synthesized via the modified TMSN₃-Ugi multi-component reaction and evaluated in vitro for antiplasmodial activity. The most potent compounds, 6b, 6c and 6j, showed IC₅₀ values in the range of 6–77 nM against chloroquine-resistant K1- and W2-strains of Plasmodium falciparum. In vitro ADME characterization of frontrunner compounds 6b and 6c indicates that these two compounds are rapidly metabolized and have a high clearance rate in human and rat liver microsomes. This result correlated well with an in vivo pharmacokinetics study, which showed low bioavailability of 6c in rats. Tentative metabolite identification was determined by LC–MS and suggested metabolic lability of groups attached to the tertiary nitrogen. Preliminary studies on 6b and 6c suggested strong inhibitory activity against the major CYP450 enzymes. In silico docking studies were used to rationalize strong inhibition of CYP3A4 by 6c. Full characterization and biological evaluation of the metabolites is currently underway in our laboratories.     

Synthesis of acetylenic sugars and uronic acids via two-carbon chain extension of d-ribose

Treatment of methyl β-d-ribofuranoside with acetone gave methyl 2,3-O-isopropylidene-β-d-ribofuranoside (1, 90%), whereas methyl α-d-ribofuranoside gave a mixture (30%) of 1 and methyl 2,3-O-isopropylidene-α-d-ribofuranoside (1a). On oxidation, 1 gave methyl 2,3-O-isopropylidene-β-d-ribo-pentodialdo-1,4-furanoside (2), whereas no similar product was obtained on oxidation of 1a. Ethynylmagnesium bromide reacted with 2 in dry tetrahydrofuran to give a 1:1 mixture (95%) of methyl 6,7-dideoxy-2,3-O-isopropylidene-β-d-allo- (3) and -α-l-talo-hept-6-ynofuranoside (4). Ozonolysis of 3 and 4 in dichloromethane gave the corresponding d-allo- and l-talo-uronic acids, characterized as their methyl esters (5 and 6) and 5-O-formyl methyl esters (5a and 6a). Ozonolysis in methanol gave a mixture of the free uronic acid and the methyl ester, and only a small proportion of the 5-O-formyl methyl ester. Malonic acid reacted with 2 to give methyl 5,6-dideoxy-2,3-O-isopropylidene-β-d-ribo-trans-hept-5-enofuranosiduronic acid (7).     

New 2-arylnaphthalenediols and triol inhibitors of HIV-1 integrase—Discovery of a new polyhydroxylated antiviral agent

A series of 13 hydroxylated 2-arylnaphthalenes have been synthesized and evaluated as HIV-1 integrase inhibitors. 7-(3,4,5-Trihydroxyphenyl)naphthalene-1,2,3-triol 1c revealed chemical instability upon storage, leading to the isolation of a dimer 5c which was also tested. In the 2-arylnaphthalene series, all compounds were active against HIV-1 IN with IC₅₀’s within the 1–10 μM range, except for 1c and 5c which displayed submicromolar activity. Antiviral activity against HIV-1 replication was measured on 1b–c and 5c. Amongst the tested molecules, only 5c was found to present antiviral properties with a low cytotoxicity on two different cell lines.     

Monodeoxy-1,4:3,6-dianhydrohexitol nitrates

Monodeoxy-1,4:3,6-dianhydrohexitol nitrates with (5) or without (6) an additional chloro substituent were synthesized, starting from 1,4:3,6-dianhydrohexitol-monoacetates, via 3 as key intermediates. Attempts to generate an unsaturated nitrate ester resulted in a DBN alkylation product (9).Both the endo- and exo-configurated monodeoxy-1,4:3,6-dianhydrohexitol nitrates have been prepared. Attempts to generate an unsaturated nitrate ester resulted in a DBN alkylation produkt.