Synthesis and structure-activity relationships of new second-generation taxoids

A series of second-generation taxoids bearing a substitutent on the C-2-benzoyl group and modifications at C-3′/C-10 positions was synthesized. These taxoids exhibited 2–3 orders of magnitude higher potency than that of paclitaxel against drug-resistant human breast cancer cell lines. It is also noteworthy that three taxoids showed almost no difference in activity against drug-resistant and drug-sensitive cell lines, which are categorized as “advanced second generation taxoids“.     

1-(3,4,5-Trimethoxyphenyl)ethane-1,2-diyl esters,a novel compound class with potent chemoreversal activity

1-(3,4,5-Trimethoxyphenyl)ethane-1,2-diyl esters, which share a fragment from (±)-3′-O-4′-O-bis(3,4-dimethoxycinnamoyl)-cis-khellactone (DMDCK) and 3′R,4′R-disubstituted-2′,2′-dimethyldihydropyrano[2,3-f]chromone (DSP), exhibited remarkable chemoreversal activity on multidrug resistant human nasopharyngeal carcinoma (KB) when combined with three anticancer drugs, paclitaxel, vincristine and doxorubicin. Among 15 novel synthesized analogs, bis-trimethoxybenzoyl derivative 15 was the most active (340-fold more active than verapamil when used with vincristine) followed by two di-cinnamoyl derivatives, 10 and 11, and then di-cyclohexanecarbonyl derivative 9. All aliphatic chain derivatives, 3–5, showed no activity. Structure-activity relationship study indicated that a di-ester structure was critical to enhance the activity resulting from the maintenance of the spatial arrangement proposed by the pharmacophore based on the verapamil-binding site. Further mechanism of action study showed 15 inhibited mainly P-glycoprotein efflux pump function, while 13 exhibited an additional multidrug resistance-associated protein efflux pump function.     

Syntheses and biological activity of C-3'-difluoromethyl-taxoids

A series of new taxoids bearing difluoromethyl group at the C-3' position and modifications at the C-10 and C-14 positions has been synthesized and their biological activities studied. The in vitro cytotoxicity assay results indicate that these newly developed taxoids exhibit comparable to several times better activity against drug-sensitive cell line LCC6-WT, and 40-70 times better activity against the corresponding drug-resistant cancer cell line LCC6-MDR as compared to that of paclitaxel. Apoptosis analysis has revealed the exceptional activity of SB-T-12843 (1e) in inducing apoptosis in both MDR-bearing and MDR-negative cancer cells.     

Seco-4-methyl-DCK derivatives as potent chemosensitizers

Twenty-five seco-4-methyl-DCK derivatives were designed, synthesized and evaluated for chemoreversal activity when combined with paclitaxel or vincristine in two drug-resistant cancer cell lines (A2780/T and KB-V) respectively. Most of the new compounds displayed moderate to significant MDR reversal activities in the P-gp overexpressing A2780/T and KB-V cells. Especially, compounds 7o and 7y showed the most potent chemosensitization activities with more than 496 and 735 reversal ratios at a concentration of 10?μM. Unexpectedly the newly synthesized compounds did not show chemosensitization activities observed in a non-P-gp overexpressing cisplatin resistant human ovarian cancer cell line (A2780/CDDP), implying that the MDR reversal effects might be associated with P-gp overexpression. Moreover, these compounds did not exhibit significant antiproliferative activities against nontumorigenic cell lines (HUVEC, HOSEC and T29) compared to the positive control verapamil at the tested concentration, which suggested better safety than verapamil. The pharmacological actions of the compounds will be studied further to explore their merit for development as novel candidates to overcome P-gp mediated MDR cancer.     

Two new glycosides from the whole plant of Anemone rivularis var. flore-minore

Phytochemical investigation on the whole plant of Anemone rivularis var. flore-minore led to the isolation of a new labdane-type diterpene glycoside (1) and a new trihydroxyfuranoid lignanoid glycoside (2), together with three known triterpene and triterpenoid glycosides (3–5). The structures of the two new compounds were elucidated as β-d-glucopyranosyl (13S)-13-hydroxy-7-oxo-labda-8,14-diene-18-oate (1) and (7S,7′R,8R,8′S)-7′-butoxy-7,9′-epoxy-4,4′,9-trihydroxy-3,3′-dimethoxylignane 9-O-β-d-glucopyranoside (2), on the basis of extensive spectral analysis and chemical evidence. Compound 1 is characterized by a glucose (Glc) esterified C-18 carboxyl group, which is a rarely encountered labdane-type diterpene glycoside in nature. The two new compounds (1 and 2) reported here are the first examples of diterpene glycoside and lignanoid glycoside found in the genus Anemone, and the known triterpene and triterpenoid glycosides (3–5) are identified for the first time from the title plant.     

Inhibition of human P-glycoprotein transport and substrate binding using a galantamine dimer

The human multidrug resistance transporter P-glycoprotein (P-gp) prevents the entry of compounds into the brain by an active efflux mechanism at the blood-brain barrier (BBB). Treatment of neurodegenerative diseases, therefore, has become a challenge and the development of new reversible inhibitors of P-gp is pertinent to overcome this problem. We report the design and synthesis of a crosslinked agent based on the Alzheimer’s disease treatment galantamine (Gal-2) that inhibits P-gp-mediated efflux from cultured cells. Gal-2 was found to inhibit the efflux of the fluorescent P-gp substrate rhodamine 123 in cancer cells that over-express P-gp with an IC₅₀ value of approximately 0.6 μM. In addition, Gal-2 was found to inhibit the efflux of therapeutic substrates of P-gp, such as doxorubicin, daunomycin and verapamil with IC₅₀ values ranging from 0.3 to 1.6 μM. Through competition experiments, it was determined that Gal-2 modulates P-gp mediated efflux by competing for the substrate binding sites. These findings support a potential role of agents, such as Gal-2, as inhibitors of P-gp at the BBB to augment treatment of neurodegenerative diseases.     

Electrolytic reduction of abscisic acid methyl ester and its free acid

Abscisic acid (ABA, 1), a plant hormone, has electrophilicity derived almost entirely from the side-chain, 3-methylpenta-2,4-dienoic acid. The electrochemical property of ABA was investigated by analysis of its cathodic reaction. ABA methyl ester (1-Me) was reduced at a peak potential of −1.6 V to give a unique and unstable bicyclic compound (5-Me) as a major product at pH 3 and 7. This finding showed that an electron was absorbed in the conjugated dienecarboxyl group, and that C-5 with a high electron density attacked C-2′ through an intramolecular nucleophilic addition. At pH 10, in addition to 5-Me, a compound 4-Me was formed by isomerization of 5-Me under alkaline conditions. For a cathodic reaction of ABA at pH 3 and 7, compound 5 was a major product as well as in the case of ABA methyl ester. However, at pH 10, a dimer (6) with an epoxy group, 1′-deoxy-ABA (7) and other compounds were formed instead of compounds 4 and 5. Compounds 4 and 5 were biologically inactive, suggesting the importance of the electrophilic side-chain of ABA for biological activity.     

Semi-synthetic isoflavones as BACE-1 inhibitors against Alzheimer’s disease

BACE-1 is considered to be one of the targets for prevention and treatment of Alzheimer’s disease (AD). We here report a novel class of semi-synthetic derivatives of prenylated isoflavones, obtained from the derivatization of natural flavonoids from Maclura pomifera. In vitro anti-AD effect of the synthesized compounds were evaluated via human recombinant BACE-1 inhibition assay. Compound 7, 8 and 13 were found to be the most active candidates which demonstrates good correlation between the computational docking and pharmacokinetic predictions. Moreover, cytotoxic studies demonstrated that the compounds are not toxic against normal and cancer cell lines. Among these three compounds, compound 7 enhance the activity of P-glycoprotein (P-gp) on A549 cancer cells and increases the activity of P-gp ATPase with a possible role on the efflux of amyloid-β across the blood- brain barrier. In conclusion, the present findings may pave the way for the discovery of a novel class of compounds to prevent and/or treat AD.     

Design and synthesis of cell potent BACE-1 inhibitors: Structure–activity relationship of P1′ substituents

Using structure-guided design, hydroxyethylamine BACE-1 inhibitors were optimized to nanomolar Aβ cellular inhibition with selectivity against cathepsin-D. X-ray crystallography illuminated the S1′ residues critical to this effort, which culminated in compounds 56 and 57 that exhibited potency and selectivity but poor permeability and high P-gp efflux.     

6,7-Dihydro-5H-pyrrolo[1,2-a] imidazoles as potent and selective α1A adrenoceptor partial agonists

Novel pyrroloimidazoles have been identified as potent partial agonists of the α_1A adrenergic receptor, with good selectivity over the α_1B, α_1D and α_2A receptor subtypes. Pyrimidine 19 possessed attractive CNS drug-like properties with good membrane permeability and no evidence for P-gp mediated efflux.     

Characterization of the Intestinal Absorption of Seven Flavonoids from the Flowers of Trollius chinensis Using the Caco-2 Cell Monolayer Model

The human Caco-2 cell monolayer model was used to investigate the absorption property, mechanism, and structure-property relationship of seven representative flavonoids, namely, orientin, vitexin, 2”-O-β-L-galactopyranosylorientin, 2”-O-β-L-galactopyranosylvitexin, isoswertisin, isoswertiajaponin, and 2”-O-(2”‘-methylbutanoyl)isoswertisin from the flowers of Trollius chinensis. The results showed that these flavonoids were hardly transported through the Caco-2 cell monolayer. The compounds with 7-OCH₃ including isoswertisin, isoswertiajaponin and 2”-O-(2”‘-methylbutanoyl)isoswertisin were absorbed in a passive diffusion manner, and their absorbability was increased in the same order as their polarity. The absorption of the remaining compounds with 7-OH including orientin, vitexin, 2”-O-β-L-galactopyranosylorientin, and 2”-O-β-L-galactopyranosylvitexin involved transporter mediated efflux in addition to passive diffusion. Among the four compounds with 7-OH, those with a free hydroxyl group at C-2” such as orientin and vitexin were the substrates of P-glycoprotein (P-gp) and that with a free hydroxyl group at C-2’ such as 2”-O-β-L-galactopyranosylorientin was the substrate of multidrug resistance protein 2 (MRP2). The results of this study also implied that the absorbability of the flavonoids should be taken into account when estimating the effective components of T. chinensis.     

Design,synthesis, radiolabeling and in vivo evaluation of potential positron emission tomography (PET) radioligands for brain imaging of the 5-HT7 receptor

Here we describe the design, synthesis, and pharmacological evaluation of a set of compounds structurally related to the high affinity serotonin 5-HT₇ receptor agonist N-(4-cyanophenylmethyl)-4-(2-diphenyl)-1-piperazinehexanamide (6, LP-211). Specific structural modifications were performed in order to maintain affinity for the target receptor and to improve the selectivity over 5-HT_1A and adrenergic α₁ receptors. The synthesized compounds have chemical features that could enable labeling with a positron emitter radioisotope (carbon-11 or fluorine-18) and lipophilicity within the range considered optimal for brain penetration and low non-specific binding. 4-[2-(4-Methoxyphenyl)phenyl]-N-(pyridin-4-ylmethyl)piperazinehexanamide (23a) and N-pyridin-4-ylmethyl-3-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]ethoxy]propanamide (26a) were radiolabeled on the methoxy group with carbon-11. Positron emission tomography (PET) analysis revealed that [¹¹C]-23a and [¹¹C]-26a were P-glycoprotein (P-gp) substrates and rapidly metabolized, resulting in poor brain uptake. These features were not predicted by in vitro tests.     

Acetylated allose-containing flavonoid glucosides from Stachys anisochila

In continuation of our chemosystematic study of Stachys (Labiatae) we have isolated the previously reported isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (1) and 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (4) and four new allose-containing flavonoid glycosides from S. anisochila. The new glycosides are hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranside] (6) as well as the three corresponding diacetyl analogues of 1, 4 and 6, isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside], 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside] and hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside]. Extensive two-dimensional NMR studies (proton-carbon correlations, COSY experiments) allowed assignment of all ¹H NMR sugar signals and a correction of the ¹³C NMR signal assignments for C-2 and C-3 of the allose.     

Chemical constituents from Oncocalyx glabratus and their biological activities

Chemical investigation of the aerial parts of Oncocalyx glabratus resulted in the isolation of three new flavan derivatives, 5,3′,4′-trihydroxyflavan 7-O-gallate (1), 5,4′-dihydroxyflavan 7-3′-O-digallate (2) and 5,3′-dihydroxyflavan 7-4′-O-digallate (3), named oncoglabrinol A, B and C, respectively, together with four known flavonols, (+)-catechin (4), (+)-catechin-7-O-gallate (5), catechin-7-4′-O-digallate (6A) and catechin-7-3′-O-digallate (6B). The structures of the compounds were established by 1D, 2D NMR and ESI-HRMS spectral analyses. The biological activity of the compounds was tested through a series of in vitro assays designed for determining cytotoxicity, antiviral activity against hepatitis B virus, and antidiabetic activity. All compounds were found non-toxic and showed moderate anti-HBV activity. Compounds 3 and 6 showed dual PPAR agonistic activity while others were not effective.     

Structure-based design of novel dihydroisoquinoline BACE-1 inhibitors that do not engage the catalytic aspartates

The structure–activity relationship of a series of dihydroisoquinoline BACE-1 inhibitors is described. Application of structure-based design to screening hit 1 yielded sub-micromolar inhibitors. Replacement of the carboxylic acid of 1 was guided by X-ray crystallography, which allowed the replacement of a key water-mediated hydrogen bond. This work culminated in compounds such as 31, which possess good BACE-1 potency, excellent permeability and a low P-gp efflux ratio.     

Synthesis of an intensely sweet chlorodeoxysucrose: Mechanism of 4′-chlorination of sucrose by sulphuryl chloride

Reaction of 6-O-acetylsucrose¹ with sulphuryl chloride in chloroform-pyridine affords, after dechlorosulphation and acetylation, a mixture of two isomeric 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-α-d-galactopyranosyl 3-O-acetyl-1,4,6-trichloro-1,4,6-trideoxy-β-d-hexulofuranosides (6 and 7) and 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-α-d-galactopyranosyl 3,4-di-O-acetyl-1,6-dichloro-1,6-dideoxy-β-d-fructofuranoside (4). Chlorination of C-4, C-1′, and C-6′ occurs by direct displacement of the initially formed chlorosulphonyloxy groups by chloride ions, but displacement of the 4′-chlorosulphate is sterically hindered. The introduction of a 4′-chloro substituent involves ring opening of intermediate 3′,4′-epoxides by chloride ions, the ribo-epoxide producing the sorbo-isomer 6 and the lyxo-epoxide giving the fructo-isomer 7. The proposed mechanism is supported by the formation of 4-chloro-4-deoxyfructofuranosides when 3′,4′-lyxo-hexulofuranosides are treated with sulphuryl chloride under the same conditions.     

Sesquiterpenoids and lignans from the fruits of Illicium simonsii Maxim

Twenty-two known compounds were isolated from the 95% alcohol extract of the fruits of Illicium simonsii Maxim, including seven sesquiterpenoids (16–22) and fifteen lignans (1–15). In the present research, compounds 3 ((7S,8R,8′S)-3,3′-dimethoxy-4,4′,9-trihydroxy-7,9′-epoxylignan-7′-one), 4 ((−)-(7′S,8S,8′R)-4,4′-dihydroxy-3,3′,5,5′-tetramethoxy-7′,9-epoxylignan-9′-ol-7-one), 5 ((+)-8-hydroxypinoresinol), 6 ((+)-8-hydroxymedioresinol), 8 ((2R,3R)-2β-(4″-hydroxy-3″-methoxybenzyl)-3α-(4′-hydroxy-3′-methoxybenzyl)-γ-butyrolactone 2-O-(β-D-glucopyranoside), 12 ((+)-8-methoxyisolariciresinol), 13 (α-conidendrin), 14 (boehmenan) and 15 (7R,8R,7′E-7′,8′-didehydro-4,7,9,9′- tetrahydroxy-3-methoxy-8-O-4′-neolignan) were reported from the Illicium genus for the first time, and compounds 1 (simulanol), 7 ((+)-secoisolariciresinol monoglucoside), 10 ((+)-9-O-β-D-glucopyranosyl lyoniresinol), 11 ((+)-isolariciresinol), 18 (neoanisatin), 19 (veranisatin A), 20 (4,5-d₂-8′-oxo-dihydrophaseic acid) and 22 (Oligandrumin A) were firstly isolated from the plant. Their structures were elucidated on the basis of NMR spectroscopic and mass spectrometric data. Moreover, the chemotaxonomic significance of the isolated compounds is discussed.     

Secondary metabolites from the leaves of the medicinal plant goldenseal (Hydrastis canadensis)

The study presented herein constitutes an extensive investigation of constituents in Hydrastis canadensis L. (Ranunculaceae) leaves. It describes the isolation and identification of two previously unknown compounds, 3,4-dimethoxy-2-(methoxycarbonyl)benzoic acid (1) and 3,5,3′-trihydroxy-7,4′-dimethoxy-6,8-C-dimethyl-flavone (2), along with the known compounds (±)-chilenine (3), (2R)-5,4′-dihydroxy-6-C-methyl-7-methoxy-flavanone (4), 5,4′-dihydroxy-6,8-di-C-methyl-7-methoxy-flavanone (5), noroxyhydrastinine (6), oxyhydrastinine (7) and 4′,5′-dimethoxy-4-methyl-3′-oxo-(1,2,5,6-tetrahydro-4H-1,3-dioxolo-[4′,5′:4,5]-benzo[1,2-e]-1,2-oxazocin)-2-spiro-1′-phtalan (8). Compounds 3–8 have been reported from other sources, but this is the first report of their presence in H. canadensis extracts. A mass spectrometry based assay was employed to demonstrate bacterial efflux pump inhibitory activity against Staphylococcus aureus for 2, with an IC₅₀ value of 180 ± 6 μM. This activity in addition to that of other bioactive compounds such as flavonoids and alkaloids, may explain the purported efficacy of H. canadensis for treatment of bacterial infections. Finally, this report includes high mass accuracy fragmentation spectra for all compounds investigated herein which were uploaded into the Global Natural Products Social molecular networking library and can be used to facilitate their future identification in H. canadensis or other botanicals.     

Understanding dihydro-β-agarofuran sesquiterpenes from Tripterygium hypoglaucum as the modulators of multi-drug resistance in HepG2/Adr cells

Multi-drug resistance (MDR) is one of the dominant reasons for the failure of cancer chemotherapy. P-glycoprotein (P-gp) over-expression in the plasma membrane of drug-resistant tumor cells promotes the efflux of chemotherapeutic agents and plays a significant role in MDR. Several investigations have suggested that dihydro-β-agarofuran sesquiterpenes are the potential modulators of MDR. However, their cellular mechanism in regulating P-gp has not been fully explored. Seven dihydro-β-agarofuran sesquiterpenes (1–7) from Tripterygium hypoglaucum was evaluated for the chemoreversal activity of HepG2/Adr cells. 1, 2, 4, 5, and 7 were active with reversal fold ranging from 47.68 to 456.90. The image-based high-screening indicated that all of the active compounds were capable of decreasing the efflux of doxorubicin (Dox). The most potent 4 did not affect the expression or subcellular distribution of P-gp. P-gp ATPase activity was stimulated by 4 in a dose-depend manner, suggesting that 4 may be the substrate of P-gp. The docking data implied that 4 took PHE 979, PHE 332, and GLN 986 to bind with P-gp. Taken together, the results demonstrated that dihydro-β-agarofuran sesquiterpenes from T. Hypoglaucum were the substrate of P-gp and potential modulators of MDR.     

The incorporation of ornithine-[2,3-13C2] into nicotine and nornicotine established by NMR

dl-Ornithine-[2,3-¹³C₂] was synthesized from acetate-[1-¹³C] and ethyl acetamidocyanoacetate-[2-¹³C]. This labelled material was mixed with dl-ornithine-[5-¹⁴C] and fed to Nicotiana glutinosa plants by the wick method. After 10 days the plants were harvested affording radioactive nicotine and nornicotine (0.14% and 0.051% specific incorporations, respectively). Even at these low specific incorporations an examination of their ¹³C NMR spectra established the incorporation of ornithine symmetrically into the pyrrolidine rings of these alkaloids. Satellites were observable at the signals due to C-2′, 3′, 4′ and 5′ positions, arising by the presence of contiguous carbons at C-2′, 3′ and C-4′, 5′.