Syntheses of 6-(2-hydroxy-6-phenylhexyl)-5,6-dihydro-2H-pyran-2-one derivatives and their cytotoxicities

The cytotoxicities against cancer cells (HL-60, HeLa) and insect cells (Sf9) of four stereoisomers of 6-(2-hydroxy-6-phenylhexyl)− 5,6-dihydro-2H-pyran-2-one (1) were evaluated, and then their structure-activity relationships examined. The 2′-dehydroxy derivative 5 of (6 R,2′R)- and (6 R,2′S)-1 showed the highest activity against HeLa cells (IC₅₀ = 1.4 μM). To evaluate the effect of the 2′-hydroxy group of 1, 6R-and 6S-oxetane derivatives were also synthesized and their activities examined. Against HeLa and HL-60 cells, the activities of the less potent stereoisomers were enhanced 3–4-fold by the introduction of the oxetane moieties at the 2′-position. Against the insect cell line (Sf9), phenyl derivative 7 showed the highest activity with an IC₅₀ value of 8.0 μM.     

A pair of new tetrahydro-naphthalenone enantiomers from Eremurus altaicus (Pall.) Stev.

A new racemic mixture of a 4-hydroxytetralone derivative, altaicusin A (1), was isolated from the whole plant of Eremurus altaicus (Pall.) Stev., together with three anthraquinones (compounds 2–4) and two naphthalene derivatives (5–6). The racemic altaicusin A (1) was further purified by chiral HPLC to yield a pair of enantiomers, (+)-(4S)-altaicusin A (1a) and (−)-(4R)-altaicusin A (1b). Their structures were established on the basis of spectroscopic analysis, including IR, HR-TOF-MS, and NMR. The absolute configurations of compounds 1a and 1b were elucidated by quantum chemical ECD calculations. Compounds 3 and 6 exhibited inhibitory activity against protein tyrosine phosphatase 1B (PTP1B).     

Synthesis and in vitro antitumor activity of novel iridium(III) complexes with enantiopure C2-symmetrical vicinal diamine ligands

Four novel iridium(III) complexes with enantiopure C₂-symmetrical vicinal diamine ligands were designed, synthesized, and characterized by FT-IR, NMR, and MS. The cytotoxicities of all of the complexes against the human solid tumor cell lines A2780, A549, KB, and MDA-MB-231 were evaluated. Both R,R-configured complexes (R,R)-5a and (R,R)-5b exhibited more potent or similar activity compared with oxaliplatin, whereas their corresponding (S,S)-isomers (S,S)-5a and (S,S)-5b were found to be mostly inactive. As indicated by the activation of caspase-3, the cleavage of PARP, and the upregulation of p53, the preliminary mechanism studies revealed that the mode of cell death initiated by (R,R)-5a in A2780 cells was predominantly p53-mediated apoptosis. In addition, the structure of (R,R)-5a was unambiguously confirmed through single crystal X-ray structure determination.     

Structure–cytotoxic activity relationship of sesquilignan,morinol A

The cytotoxic activities of sesquilignans, (7S,8S,7′R,8′R)- and (7R,8R,7′S,8′S)-morinol A and (7S,8S,7′S,8′S)- and (7R,8R,7′R,8′R)-morinol B were compared, showing no significant difference between stereoisomers (IC₅₀ = 24–35 μM). As a next stage, the effect of substituents at 7, 7′, and 7″-aromatic ring on the activity was evaluated to find out the higher activity of (7S,8S,7′R,8′R)-7,7′,7″-phenyl derivative 18 (IC₅₀ = 6–7 μM). In the research on the structure–activity relationship of 7″-position of (7S,8S,7′R,8′R)-7,7′,7″-phenyl derivative 18, the most potent compounds were 7,7′,7″-phenyl derivative 18 (IC₅₀ = 6 μM) against HeLa cells. Against HL-60 cells, 7″-(4-nitrophenyl)-7,7′-phenyl derivative 33 and 7″-hexyl-7,7′-phenyl derivative 37 (IC₅₀ = 5 μM) showed highest activity. We discovered the compounds showed four to sevenfold potent activity than that of natural (7S,8S,7′R,8′R)-morinol A. It was also confirmed that the 7′-benzylic hydroxy group have an important role for exhibiting activity, on the other hand, the resonance system of cinnamyl structure is not crucial for the potent activity.     

Stereoselective inhibition of serotonin re-uptake and phosphodiesterase by dual inhibitors as potential agents for depression

Multi-target compounds where more than one functional activity is incorporated into the same molecule may have advantages in treating disease states. Selective serotonin re-uptake inhibitors (SSRIs)^a (i.e., (R)- and (S)-norfluoxetine) were chemically linked to a PDE4 inhibitor via a five carbon bridge. The new dual PDE4 inhibitor/SSRIs (i.e., (R)-8 and (S)-8) showed moderately potent but highly selective serotonin re-uptake inhibition (IC₅₀ values of 173 and 42 nM, respectively) in vitro. The dual PDE4 inhibitor/SSRIs (R)-8 and (S)-8 also inhibited PDE4D2 (i.e., K_i values of 106 and 253 nM, respectively). Due to the synergistic functional activity, PDE4 inhibitor/SSRIs may be effective in treating diseases such as depression.     

Inhibition of serotonin and norepinephrine reuptake and inhibition of phosphodiesterase by multi-target inhibitors as potential agents for depression

Compounds possessing more than one functional activity incorporated into the same molecule may have advantages in treating complex disease states. Balanced serotonin/norepinephrine reuptake inhibitors (SNRIs) (i.e., (R)- and (S)-norduloxetine) were chemically linked to a PDE4 inhibitor via a five carbon bridge. The new dual SNRI/PDE4 inhibitors (i.e., (R)-15 and (S)-15) showed moderately potent serotonin reuptake inhibition (IC₅₀ values of 442 and 404 nM, respectively) but low reuptake inhibition of norepinephrine (IC₅₀ values of 2097 and 2190 nM, respectively) in vitro. The dual SNRI/PDE4 inhibitors (i.e., (R)-15 and (S)-15) also inhibited PDE4D2 (i.e., K_i values of 23 and 45 nM, respectively). Due to their synergistic functional activity, SNRI/PDE4 inhibitors may be effective in treating diseases such as depression.     

Anti-AIDS agents 84. Synthesis and anti-human immunodeficiency virus (HIV) activity of 2′-monomethyl-4-methyl- and 1′-thia-4-methyl-(3′R,4′R)-3′,4′-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) analogs

In a continuing investigation into the pharmacophores and structure–activity relationship (SAR) of (3′R,4′R)-3′,4′-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) as a potent anti-HIV agent, 2′-monomethyl substituted 1′-oxa, 1′-thia, 1′-sulfoxide, and 1′-sulfone analogs were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. Among them, 2′S-monomethyl-4-methyl DCK (5a)³ and 2′S-monomethyl-1′-thia-4-methyl DCK (7a) exhibited potent anti-HIV activity with EC₅₀ values of 40.2 and 39.1 nM and remarkable therapeutic indexes of 705 and 1000, respectively, which were better than those of the lead compound DCK in the same assay. In contrast, the corresponding isomeric 2′R-monomethyl-4-methyl DCK (6) and 2′R-monomethyl-1′-thia-4-methyl DCK (8) showed much weaker inhibitory activity against HIV-1 replication. Therefore, the bioassay results suggest that the spatial orientation of the 2′-methyl group in DCK analogs can have important effects on anti-HIV activity of this compound class.     

S1P1-selective agonist prodrug IMMH002 is phosphorylated in rats to form an S-configured enantiomer: Synthesis,verification, and biological activity of the in vivo active metabolite

IMMH002 (1), a prodrug for a sphingosine-1-phosphate receptor 1 (S1P₁) agonist, is converted to the monophosphate ester, which has an immunomodulatory effect. Starting from prochiral amino alcohol 1, racemic and enantiomerically pure phosphates of 1 were synthesized. Pure enantiomers were obtained after the chiral resolution of the key intermediate by chiral high-performance liquid chromatography and the absolute configuration was determined by circular dichroism. In the in vitro homogeneous time-resolved fluorescence-IP1 functional assay, the (S)-enantiomer showed much higher S1P₁ activity and selectivity than the (R)-enantiomer. In the pharmacokinetic study, the ex vivo o-phthaldialdehyde derivatization protocol showed that the phosphate of 1 in rats was the S-configured enantiomer with >99% enantiomeric excess.     

Synthesis and biological evaluation of enantiomerically pure glyceric acid derivatives as LpxC inhibitors

Inhibitors of the UDP-3-O-[(R)-3-hydroxymyristoyl]-N-acetylglucosamine deacetylase (LpxC) represent a promising class of novel antibiotics, selectively combating Gram-negative bacteria. In order to elucidate the impact of the hydroxymethyl groups of diol (S,S)-4 on the inhibitory activity against LpxC, glyceric acid ethers (R)-7a, (S)-7a, (R)-7b, and (S)-7b, lacking the hydroxymethyl group in benzylic position, were synthesized. The compounds were obtained in enantiomerically pure form by a chiral pool synthesis and a lipase-catalyzed enantioselective desymmetrization, respectively. The enantiomeric hydroxamic acids (R)-7b (K_i = 230 nM) and (S)-7b (K_i = 390 nM) show promising enzyme inhibition. However, their inhibitory activities do not substantially differ from each other leading to a low eudismic ratio. Generally, the synthesized glyceric acid derivatives 7 show antibacterial activities against two Escherichia coli strains exceeding the ones of their respective regioisomes 6.     

Enantioselective resolution of side-chain modified gem-difluorinated alcohols catalysed by Candida antarctica lipase B and monitored by capillary electrophoresis

An enzymatic alternative to the chemical synthesis of chiral gem-difluorinated alcohols has been developed. The method is highly effective and stereoselective, feasible at laboratory temperature, avoiding the use of toxic heavy metal catalysts which is an important benefit in medicinal chemistry including the synthesis of drugs and drug precursors. Candida antarctica lipases A and B were applied for the enantioselective resolution of side-chain modified gem-difluorinated alcohols, (R)- and (S)-3-benzyloxy-1,1-difluoropropan-2-ols (1a and 1b), compounds serving as chiral building blocks in the synthesis of various bioactive molecules bearing a gem-difluorinated grouping. The catalytic activity of these lipases was investigated for the chiral acetylation of 1a and 1b in non-polar solvents using vinyl acetate as an acetyl donor. The dependence of the reaction course on various substrate and enzyme concentrations, reaction time, and temperature was monitored by chiral capillary electrophoresis (CE) using sulfobutyl ether β-cyclodextrin as a stereoselective additive of the aqueous background electrolyte. The application of CE, NMR, and MS methods has proved that the complex enzyme effect of Candida antarctica lipase B leads to the thermodynamically stable (S)-enantiomer 1b instead of the expected acetylated derivatives. In contrast, the enantioselective acetylation of racemic alcohol 1 was observed as a kinetically controlled process, where (R)-enantiomer 1a was formed as the main product. This process was followed by enzymatic hydrolysis and chiral isomerisation. Finally, single pure enantiomers 1a and 1b were isolated and their absolute configurations were assigned from NMR analysis after esterification with Mosher’s acids.     

Design,synthesis and in vitro evaluation of a series of α-substituted phenylpropanoic acid PPARγ agonists to further investigate the stereochemistry–activity relationship

We previously demonstrated that the α-benzylphenylpropanoic acid-type PPARγ-selective agonist 6 exhibited a reversed stereochemistry–activity relationship, that is, the (R)-enantiomer is a more potent PPARγ agonist than the (S)-enantiomer, compared with structurally similar α-ethylphenylpropanoic acid-type PPAR agonists. Here, we designed, synthesized and evaluated the optically active α-cyclohexylmethylphenylpropanoic acid derivatives 7 and α-phenethylphenylpropanoic acid derivatives 8, respectively. Interestingly, α-cyclohexylmethyl derivatives showed reversal of the stereochemistry–activity relationship [i.e., (R) more potent than (S)], like α-benzyl derivatives, whereas α-phenethyl derivatives showed the ‘normal’ relationship [(S) more potent than (R)]. These results suggested that the presence of a branched carbon atom at the β-position with respect to the carboxyl group is a critical determinant of the reversed stereochemistry–activity relationship.     

Dolabellane diterpenoids from Aglaia odorata

Dolabellane diterpenoids, (1R,3E,7E,10S,11S,12R)-dolabella-3,7-dien-10,18-diol (1), (1R,3S,7E,11S,12R)-dolabella-4(16),7-dien-3,18-diol (2), (1R,7E,11S,12R)-18-hydroxydolabella-4(16),7-dien-3-one (3), (1R,3S,4S,7E,11S,12R)-3,4-epoxydolabella-7-en-18-ol (4), and (1R,3R,7E,11S,12R)-dolabella-4(16),7,18-trien-3-ol (5), were obtained from the ornamental plant Aglaia odorata. Their structures were characterized on the basis of spectroscopic analyses and further confirmed by X-ray diffraction. Compounds 1 and 5 showed weak cytotoxicity against the human myeloid leukemia HL-60, hepatocellular carcinoma SMMC-7721, and lung cancer A-549 cells.     

Asymmetric synthesis and effect of absolute stereochemistry of YCZ-2013, a brassinosteroid biosynthesis inhibitor

The four stereoisomers of 2RS,4RS-1-[[2-(2,4-dichlorophenyl)-4-(2-(2-propenyloxy)phenoxymethyl)-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole (YCZ-2013), a novel brassinosteroid biosynthesis inhibitor, were prepared. The diastereomers of 2RS,4R-5 and 2RS,4S-5 were prepared by using the corresponding optically pure R and S toluene-4-sulfonic acid 2,3-dihydroxypropyl ester (R-4,S-4). The enatiomerically and diastereomerically pure acetonide (5) was obtained by a method involving diastereoselective crystallisation of the tosylate salt, followed by re-equilibration with the mother liquor and chromatography. The optical purity of four target compounds (YCZ-2013) was confirmed by chiral high-performance liquid chromatography (HPLC) and NMR. The effects of these stereoisomers on Arabidopsis stem elongation indicated that the cis isomers of 2S,4R-YCZ-2013 and 2R,4S-YCZ-2013 exhibited potent inhibitory activity with IC₅₀ values of approximately 24 ± 3 and 24 ± 2 nM, respectively. The IC₅₀ values of the trans isomers of 2S,4S-YCZ-2013 and 2R,4R-YCZ-2013 are approximately 1510 ± 50 and 3900 ± 332 nM, respectively. Co-application of brassinolide (10 nM), the most potent BR, and GA₃ (1 μM) to Arabidopsis seedlings grown in the dark with 2R,4S-YCZ-2013 and 2S,4R-YCZ-2013 revealed that brassinolide recovered the induced dwarfism of Arabidopsis seedlings, whereas GA₃ showed no effect.     

Discovery of selective and orally available spiro-3-piperidyl ATP-competitive MK2 inhibitors

The identification of a potent, selective, and orally available MK2 inhibitor series is described. The initial absence of oral bioavailability was successfully tackled by moving the basic nitrogen of the spiro-4-piperidyl moiety towards the electron-deficient pyrrolepyridinedione core, thereby reducing the pK_a and improving Caco-2 permeability. The resulting racemic spiro-3-piperidyl analogues were separated by chiral preparative HPLC, and the activity towards MK2 inhibition was shown to reside mostly in the first eluting stereoisomer. This led to the identification of new MK2 inhibitors, such as (S)-23, with low nanomolar biochemical inhibition (EC₅₀ 7.4 nM) and submicromolar cellular target engagement activity (EC₅₀ 0.5 μM).     

Identification of RC-33 as a potent and selective σ1 receptor agonist potentiating NGF-induced neurite outgrowth in PC12 cells. Part 2: g-Scale synthesis,physicochemical characterization and in vitro metabolic stability

Strong pharmacological evidences indicate that σ1 receptors are implicated in the pathophysiology of all major CNS disorders. In the last years our research group has conducted extensive studies aimed at discovering novel σ1 ligands and we recently selected (R/S)-RC-33 as a novel potent and selective σ1 receptor agonist. As continuation of our work in this field, here we report our efforts in the development of this new σ1 receptor agonist. Initially, we investigated the binding of (R) and (S) enantiomers of RC-33 to the σ1 receptor by in silico experiments. The close values of the predicted affinity of (R)-RC-33 and (S)-RC-33 for the protein evidenced the non-stereoselective binding of RC-33 to the σ1 receptor; this, in turn, supported further development and characterization of RC-33 in its racemic form. Subsequently, we set-up a scaled-up, optimized synthesis of (R/S)-RC-33 along with some compound characterization data (e.g., solubility in different media and solid state characterization by thermal analysis techniques). Finally, metabolic studies of RC-33 in different biological matrices (e.g., plasma, blood, and hepatic S9 fraction) of different species (e.g., rat, mouse, dog, and human) were performed. (R/S)-RC-33 is generally stable in all examined biological matrices, with the only exception of rat and human liver S9 fractions in the presence of NADPH. In such conditions, the compound is subjected to a relevant oxidative metabolism, with a degradation of approximately 65% in rat and 69% in human.Taken together, our results demonstrated that (R/S)-RC-33 is a highly potent, selective, metabolically stable σ1 agonist, a promising novel neuroprotective drug candidate.     

Design,synthesis and cytotoxicity of novel 3′-N-alkoxycarbonyl docetaxel analogs

By-product 9a exhibited potent cytotoxicity against both SK-OV-3 and A549 cell lines. The structure of 9a was characterized using 1D and 2D NMR experiments and confirmed by synthesis to afford a diastereomeric mixture (16a) that was identical to 9a, as well as a pair of diastereomers (R)-16b and (S)-16c. The preliminary SAR study demonstrated that analogs with an (R)-configuration were slightly more potent than analogs with an (S)-configuration. In addition, α,α-gem-dimethyl analogs 16g–i were the most potent analogs in this series, exhibiting similar potency to docetaxel and greater potency than Taxol against the SK-OV-3 cell line. For the A549 cell line, analogs 16g–i were more potent (>65-fold) than both docetaxel and Taxol.     

Enantiomeric lignans with anti-β-amyloid aggregation activity from the twigs and leaves of Pithecellobium clypearia Benth

To develop potential agents for slowing the progression of Alzheimer′s disease, two pairs of new enantiomeric lignans, including a couple of rarely 8′,9′-dinor-3′,7-epoxy-8,4′-oxyneolignanes named (7S, 8S)- and (7R, 8R)-pithecellobiumin A (1a/1b) and a pair of 2′,9′-epoxy-arylnaphthalenes named (7R, 8R, 8′R)- and (7S, 8S, 8′S)-pithecellobiumin B (2a/2b) were separated by chiral high performance liquid chromatography (HPLC). Their planar structures were elucidated by spectroscopic data analyses. The absolute configurations were determined by comparing of experimental and calculated electronic circular dichroism (ECD). The inhibitory activity on Aβ aggregation of all optical pure compounds was tested by ThT assay. Interestingly, enantiomeric inhibitors 1a (62.1%) and 1b (81.6%) exhibited different degrees of anti-Aβ aggregation activity. However, 2a (65.4%) and 2b (68.4%) showed similar inhibition rate. The different inhibition profiles were explained by molecular dynamics and docking simulation studies.     

α-Santalol derivatives from Santalum album and their cytotoxic activities

A bioassay-guided fractionation of the heartwood of Santalum album led to the isolation of seven α-santalol derivatives including (9S,10E)-9-hydroxy-α-santalal, (10R,11S)-10,11-dihydroxy-α-santalol, (9E)-11,13-dihydroxy-α-santalol, and (10E)-12-hydroxy-α-santalic acid. Their structures were determined on the basis of results of spectroscopic analysis, including two-dimensional (2D) NMR spectroscopic data. The isolated compounds and derivatives were evaluated for cytotoxicity against HL-60 human promyelocytic leukemia cells and TIG-3 normal human diploid fibroblasts. Of these (9S,10E)-9-hydroxy-α-santalal, exhibited tumor-selective cytotoxicity. The apoptosis induction properties of sesquiterpenes with cytotoxic potency in HL-60 cells are also described.     

Synthesis and pharmacological evaluation of optically pure,novel carbonyl guanidine derivatives as dual 5-HT2B and 5-HT7 receptor antagonists

A series of 9-disubstituted N-(9H-fluorene-2-carbonyl)guanidine derivatives have been discovered as potent and orally active dual 5-HT_2B and 5-HT₇ receptor antagonists. Upon screening several compounds, N-(diaminomethylene)-4′,5′-dihydro-3′H-spiro[fluorene-9,2′-furan]-2-carboxamide (17) exhibited potent affinity for both 5-HT_2B (K_i = 5.1 nM) and 5-HT₇ (K_i = 1.7 nM) receptors with high selectivity over 5-HT_2A, 5-HT_2C, α₁, D₂ and M₁ receptors. Optical resolution of the intermediate carboxylic acid 16 via the formation of diastereomeric salts using chiral alkaloids gave the optically pure compounds (R)-17 and (S)-17. Both enantiomers suppressed 5-HT-induced dural protein extravasation in guinea pigs in a dose-dependent manner and the amount of leaked protein was suppressed to near normal levels when orally administrated at 10 mg/kg. (R)-17 and (S)-17 were therefore selected as candidates for human clinical trials.