6-methoxy-1,2,3,4-tetrahydroquinoline moiety in prior leads
2-chloro- and 2-methyl-4-(6-methoxy-3,4-dihydroquinolin-1(2H)-yl)quinazoline (1a and 1b)
was modified to produce 4-(N-cycloamino)quinazolines
(4a–c and 5a–m). The new compounds were evaluated in cytotoxicity and tubulin
inhibition assays, resulting in the discovery of new tubulin-polymerization
2(1H)-one (5f), the most potent compound,
exhibited high in vitro cytotoxic activity (GI50 1.9–3.2
nM), significant potency against tubulin assembly (IC50 0.77 μM), and substantial inhibition of colchicine binding
(99% at 5 μM). In mechanism studies, 5f caused
cell arrest in G2/M phase, disrupted microtubule formation, and competed
mostly at the colchicine site on tubulin. Compound 5f and N-methylated analogue 5g were evaluated in nude
mouse MCF7 xenograft models to validate their antitumor activity.
Compound 5g displayed significant in vivo activity (tumor
inhibitory rate 51%) at a dose of 4 mg/kg without obvious toxicity,
whereas 5f unexpectedly resulted in toxicity and death
at the same dose.
Structural optimizations of the prior lead 1a led to the discovery of a series of N-aryl-6-methoxy-1,2,3,4-tetrahydroquinoline derivatives as a novel class of tubulin polymerization inhibitors targeted at the colchicine binding site. The most active compound 6d showed extremely high cytotoxicity against a human tumor cell line panel (A549, KB, KBvin, and DU145) with GI50 values ranging from 1.5 to 1.7 nM, significantly more potent than paclitaxel, especially against the drug-resistant KBvin cell line, in the same assays. Analogues 5f, 6b, 6c, and 6e were also quite potent, with a GI50 range of 0.011–0.19 μM. In further studies, active compounds 6b–6e and 5f significantly inhibited tubulin assembly, with IC50 values of 0.92 to 1.0 μM and strongly inhibited colchicine binding to tubulin, with inhibition rates of 75–99% (at 5 μM), comparable with or more potent than combretastatin A-4 (IC50 0.96 μM). Current studies included design, synthesis, and biological evaluations of 24 new compounds (series 3–6). Related SAR analysis, molecular modeling, and evaluation of essential drug-like properties, i.e. water solubility, log P, and in vitro metabolic stability, were also performed.
N-aryl-6-methoxy-1,2,3,4-tetrahydroquinolines; cytotoxicity; tubulin polymerization inhibitors; colchicine binding site
Five novel tigliane-type diterpenes, stelleracins A–E (3–7), a novel flavanone dimer, chamaeflavone A (8), and six known compounds were isolated from roots of Stellera chamaejasme. Their structures were elucidated by extensive spectroscopic analyses. The isolated compounds were evaluated for anti-HIV activity in MT4 cells. New compounds 3–5 showed potent anti-HIV activity (EC90 0.00056–0.0068 μM) and relatively low or no cytotoxicity (IC50 4.4–17.2 μM). These new compounds represent promising new leads for development into anti-AIDS clinical trial candidates.
Bevirimat (1, BVM) is an anti-HIV agent that blocks HIV-1 replication by interfering with HIV-1 Gag-SP1 processing at a late stage of viral maturation. However, clinical trials of 1 have revealed a high baseline drug resistance that is attributed to naturally-occurring polymorphisms in HIV-1 Gag. To overcome the drug resistance, 28 new derivatives of 1 were synthesized and tested against compound 1-resistant (BVM-R) HIV-1 variants. Among them, compound 6 exhibited much improved activity against several HIV-1 strains carrying BVM-R polymorphisms. Compound 6 was at least 20-fold more potent than 1 against the replication of NL4-3/V370A, which carries the most prevalent clinical BVM-R polymorphism in HIV-1 Gag-SP1. Thus, compound 6 merits further development as a potential anti-AIDS clinical trial candidate.
Betulinic acid; Bevirimat; HIV-1; Maturation inhibitors; Bevirimat-resistance
Accumulation of aberrant protein aggregates, such as
peptide (Aβ), due to decreased proteasome activities, might
contribute to the neurodegeneration in Alzheimer's disease. In this
study, lithocholic acid derivatives 3α-O-pimeloyl-lithocholic
acid methyl ester (2) and its isosteric isomer (6) were found to activate the chymotrypsin-like activity of
the proteasome at an EC50 of 7.8 and 4.3 μM, respectively.
Replacing the C24 methyl ester in 2 with methylamide
resulted in a complete devoid of proteasome activating activity. Epimerizing
the C3 substituent from an α to β orientation transformed
the activator into a proteasome inhibitor. Unlike the cellular proteasome
activator PA28, proteasome activated by 2 was not inhibited
by Aβ. Furthermore, 2 potently antagonized the
inhibitory effect of Aβ on the proteasome. In summary, compound 2 represents a novel class of small molecules that not only
activates the proteasome but also antagonizes the inhibitory effect
of Aβ on the proteasome.
proteasome activator; lithocholic acid; Alzheimer's
disease; amyloid β
In a continuing study of bevirimat (2), the anti-HIV-maturation clinical trials agent, 28 new betulinic acid (BA, 1) derivatives were designed and synthesized. Among these compounds, 17, with a C-28 MEM ester moiety, and 22, with a C-28 ethyl hexanoate, increased the anti-HIV replication activity compared with 2 by two-fold, while compounds 40–41 and 48–49, with C-28 piperazine or piperidine amide substitutions, increased the activity by three- to fifteen-fold. The best new compound 41 exhibited an anti-HIV IC50 value of 0.0059 μM, compared with 0.087 μM for 2. All of the active compounds showed only anti-maturation effects, as confirmed by TZM-bl assay, in blocking the HIV replication. The results suggest that proper C-28 substitutions can further enhance the anti-maturation activity of 2, without any anti-entry effects. Thus, 41 may serve as a promising new lead for development of anti-AIDS clinical trial candidates.
This article reviews the antitumor and anti-HIV activities of naturally occurring triterpenoids, including the lupane, ursane, oleanane, lanostane, dammarane, and miscellaneous scaffolds. Structure–activity relationships of selected natural compounds and their synthetic derivatives are also discussed.
This review discusses recent progress in the development of anti-HIV agents targeting the viral entry process. The three main classes (attachment inhibitors, co-receptor binding inhibitors, and fusion inhibitors) are further broken down by specific mechanism of action and structure. Many of these inhibitors are in advanced clinical trials, including the HIV maturation inhibitor bevirimat, from the authors’ laboratories. In addition, the CCR5 inhibitor maraviroc has recently been FDA-approved. Possible roles for these agents in anti-HIV therapy, including treatment of virus resistant to current drugs, are also discussed.
HIV entry inhibitors; attachment inhibitors; co-receptor binding inhibitors; fusion inhibitors; maraviroc (MVC; UK-427, 857); enfuvirtide (T20;fuzeon); bevirimat (DSB;PA-457)
Twenty-one new 4-substituted diarylaniline compounds (DAANs) (Scheme 2, series 13, 14, and 15) were designed, synthesized, and evaluated against wild-type and drug resistant HIV-1 viral strains. As a result, approximately a dozen new DAANs showed high potency with low nano- to sub-nanomolar EC50 values ranging from 0.2 to 10 nM. The three most promising compounds 14e, 14h, and 15h exhibited high potency against wild-type and drug-resistant viral strains with EC50 values at the sub-nanomolar level (0.29–0.87 nM), and were comparable to or more potent than the new NNRTI drug riplivirine (2) in the same assays. Drug-like physicochemical property assessments revealed that the most active DAANs (EC50 <10 nM) have better aqueous solubility (>1–90 μg/mL at pH 7.4 and pH 2) and metabolic stability in vitro than 2, as well as desirable log P values (<5) and polar surface area (PSA) (<140 Å2). These promising results warrant further development of this novel compound class as potential potent anti-AIDS clinical trial candidates.
Betulinic acid derivatives modified at the C28 position are HIV-1entry inhibitors such as compound A43D; however, modified at the C3 position instead of C28 give HIV-1 maturation inhibitor such as bevirimat. Bevirimat exhibited promising pharmacokinetic profiles in clinical trials, but its effectiveness was compromised by the high baseline drug resistance of HIV-1 variants with polymorphism in the putative drug binding site. In an effort to determine whether the viruses with bevirimat resistant polymorphism also altered their sensitivities to the betulinic acid derivatives that inhibit HIV-1 entry, a series of new betulinic acid entry inhibitors were synthesized and tested for their activities against HIV-1 NL4-3 and NL4-3 variants resistant to bevirimat. The results show that the bevirimat resistant viruses were approximately 5- to10-fold more sensitive to three new glutamine ester derivatives (13, 15 and 38) and A43D in an HIV-1 multi-cycle replication assay. In contrast, the wild type NL4-3 and the bevirimat resistant variants were equally sensitive to the HIV-1 RT inhibitor AZT. In addition, these three new compounds markedly improved microsomal stability compared to A43D.
HIV-1; Entry inhibitor; Maturation inhibitor; Betulinic acid; Berivimat; Berivimat-resistance
Accumulation of aberrant protein aggregates, such as amyloid beta peptide (Aβ), due to decreased proteasome activities might contribute to the neurodegeneration in Alzheimer's disease. In this study, lithocholic acid derivatives 3α-O-pimeloyl-lithocholic acid methyl ester (2) and its isosteric isomer (6) were found to activate the chymotrypsin-like activity of the proteasome at an EC50 of 7.8 and 4.3 μM, respectively. Replacing the C24 methyl ester in 2 with methylamide resulted in a complete devoid of proteasome activating activity. Epimerizing the C3 substituent from an alpha to beta orientation transformed the activator into a proteasome inhibitor. Unlike the cellular proteasome activator PA28, proteasome activated by 2 was not inhibited by Aβ. Furthermore, 2 potently antagonized the inhibitory effect of Aβ on the proteasome. In summary, compound 2 represents a novel class of small molecules that not only activates the proteasome but also antagonizes the inhibitory effect of Aβ on the proteasome.
proteasome activator; lithocholic acid; Alzheimer's disease; amyloid beta
3-Hydroxymethyl-4-methyl-DCK (3, HMDCK) was discovered previously as a potent HIV non-nucleoside reverse transcriptase inhibitor (NNRTIs) (EC50: 0.004 μM, TI: 6225) with a novel mechanism of action. It exerts anti-HIV activity by inhibiting the production of HIV-1 double-stranded viral DNA from a single-stranded DNA intermediate, rather than blocking the generation of single-stranded DNA from a RNA template, which is the mechanism of action of current HIV-1 RT inhibitors. However, the insufficient metabolic stability of 3 limits its further clinical development. In the current study, a series of ester prodrugs of 3 was designed and synthesized to explore the new drug candidates as NNRTIs. The l-alanine ester prodrug 10 exhibited desirable pharmacokinetic properties in vitro and in vivo and showed improved oral bioavailability of 26% in rat, and would be a potential clinical candidate as a new anti-AIDS drug.
3-Hydroxymethyl-4-methyl-DCK; Synthesis; Pharmacokinetic; Prodrug
In the present study, a new strategy to link AZT with betulin/betulinic acid (BA) by click chemistry was designed and achieved. This conjugation via a triazole linkage offers a new direction for modification of anti-HIV triterpenes. Click chemistry provides an easy and productive way for linking two molecules, even when one of them is a large natural product. Among the newly synthesized conjugates, compounds 15 and 16 showed potent anti-HIV activity with EC50 values of 0.067 and 0.10 µM, respectively, which are comparable to that of AZT (EC50: 0.10 µM) in the same assay.
Betulin; Betulinic acid; AZT; Anti-HIV; Click chemistry
The current optimization of 2,4-diarylaniline analogs (DAANs) on the central phenyl ring provided a series of new active DAAN derivatives 9a–9e, indicating an accessible modification approach that could improve anti-HIV potency against wild-type and resistant strains, aqueous solubility, and metabolic stability. A new compound 9e not only exhibited extremely high potency against wild-type virus (EC50 0.53 nM) and several resistant viral strains (EC50 0.36 – 3.9 nM), but also showed desirable aqueous solubility and metabolic stability, which were comparable or better than those of the anti-HIV-1 drug TMC278 (2). Thus, new compound 9e might be a potential drug candidate for further development of novel next-generation NNRTIs.
Diarylaniline; NNRTIs; lead optimization; anti-HIV agents
Six 3′R,4′R-di-O-(S)-camphanoyl-2′,2′-dimethyldihydropyrano[2,3-f]chromone (DCP) and two 3′R,4′R-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) derivatives were designed, synthesized, and evaluated for inhibition of HIV-1NL4-3 replication in TZM-bl cells. 2-Ethyl-2′-monomethyl-1′-oxa- and -1′-thia-DCP (5a, 6a), as well as 2-ethyl-1′-thia-DCP (7a) exhibited potent anti-HIV activity with EC50 values of 30, 38 and 54 nM and therapeutic indexes of 152.6, 48.0 and 100.0, respectively, which were better than or comparable to those of the lead compound 2-ethyl-DCP in the same assay. 4-Methyl-1′-thia-DCK (8a) also showed significant inhibitory activity with an EC50 of 128 nM and TI of 237.9.
2′-Monomethyl-1′-oxa-DCP; 2′-Monomethyl-1′-thia-DCP; 2-Ethyl-1′-thia-DCP; 4-Methyl-1′-thia-DCK; Anti-HIV activity
In this study, 22 new betulinic acid (BA) derivatives were synthesized and tested for their inhibition of the chymotrypsin-like activity of 20S proteasome. From the SAR study, we concluded that the C-3 and C-30 positions are the pharmacophores for increasing the proteasome inhibition effects, and larger lipophilic or aromatic side chains are favored at these positions. Among the BA derivatives tested, compounds 13, 20, and 21 showed the best proteasome inhibition activity with IC50 values of 1.42, 1.56, and 1.80 µM, respectively, which are three- to four-fold more potent than the proteasome inhibition controls LLM-F and lactacystin.
In a continuing study of novel anti-HIV agents with drug-like structures and properties, 30 1′-O-, 1′-S-, 4′-O- and 4′-substituted-2′,3′-seco-3′-nor DCP and DCK analogues (8–37) were designed and synthesized. All newly synthesized seco-compounds were screened against HIV-1NL4-3 and a multiple reverse transcriptase (RT) inhibitor-resistant (RTMDR) strain in the TZM-bl cell line, using seco-DCK (7) and 2-ethyl-DCP (4) as controls. Several compounds (14, 18, 19, 22–24, and 32) exhibited potent anti-HIV activity with EC50 values ranging from 0.93 to 1.93 μM and therapeutic index (TI) values ranging from 20 to 39. 1′-O-Isopropoxy-2′,3′-seco-3′-nor-DCP (12) showed the greatest potency among the newly synthesized compounds with EC50 values of 0.47 and 0.88 μM, and TI of 96 and 51, respectively, against HIV-1NL4-3 and RTMDR strains. The seco-compounds exhibited better chemical stability in acidic conditions compared with DCP and DCK compounds. Overall, the results suggested that seco-DCP analogues with simplified structures may be more favorable for development as novel anti-HIV candidates.
2′, 3′-Seco-3′-nor-DCPs; Anti-HIV activity; Structure–activity relationship (SAR)
We prepared 1-(4′-azido-2′-deoxy-2′-fluoro-β -D-arabinofuranosyl)cytosine (10) and its hydrochloride salt (11) as potential antiviral agents based on the favorable antiviral profiles of 4′-substituted nucleosides. Compounds 10 and 11 were synthesized from 1,3,5-O-tribenzoyl-2-deoxy-2-fluoro-D-arabinofuranoside in multiple steps, and their structures were unequivocally established by IR, 1H NMR, 13C NMR, and 19F NMR spectroscopy, HRMS, and X-ray crystallography. Compounds 10 and 11 exhibited potent anti-HIV-1 activity (EC50: 0.3 and 0.13 nM, respectively) without significant cytotoxicity in concentrations up to 100 μM. Compound 11 exhibited extremely potent anti-HIV activity against NL4-3 (wild-type), NL4-3 (K101E), and RTMDR viral strains, with EC50 values of 0.086, 0.15, and 0.11 nM, respectively. Due to the high potency of 11, it was also screened against an NIH Reagent Program NRTI-resistant virus panel containing eleven mutated viral strains and for cytotoxicity against six different human cell lines. The results of this screening indicated that 11 is a novel NRTI that could be developed as an anti-AIDS clinical trial candidate to overcome drug-resistance issues.
4′-Azido-2′-deoxy-2′-fluoro nucleosides; Anti-HIV activity; Nucleoside reverse transcriptase inhibitor (NRTI); Drug resistance
Three novel 1-alkyldaphnane-type diterpenes, stelleralides A–C (4–6), and five known compounds were isolated from the roots of Stellera chamaejasme L. The structures of 4–6 were elucidated by extensive spectroscopic analyses. Several isolated compounds showed potent anti-HIV activity. Compound 4 showed extremely potent anti-HIV activity (EC90 0.40 nM) with the lowest cytotoxicity (IC50 4.3 μM), and appears to be a promising compound for development into anti-AIDS clinical trial candidates.
Two new saponins, panajaponol (1) and pseudoginsenoside RT1 butyl ester (2), together with 35 known compounds (3–37), were isolated from the roots of Panax japonicus. The structures of 1 and 2 were elucidated on the basis of spectroscopic analysis and chemical methods. Furthermore, a LC-MS/MS method was developed for confirming 2, 3, and 8 as natural compounds containing a butyl ester group. This method should be useful for distinguishing between minor natural and artifactual compounds in Panax species. Moreover, compounds 3, 6, 8, 9, 11, 13, and 15 exhibited strong inhibition of superoxide anion generation and elastase release by human neutrophils in response to formyl-L-methionyl-L-leucyl-L-phenylalanine/cytochalasin B (fMLP/CB), with IC50 values ranging from 0.78 to 43.6 μM. In addition, 1 showed greater than two- to three-fold selective cytotoxic activity against KB and DU145 cancer cell lines.
A series of novel bichalcone analogs were synthesized and evaluated in lipopolysaccharide (LPS)-activated microglial cells as inhibitors of nitric oxide (NO) and for in vitro anticancer activity using a limited panel of four human cancer cell lines. All analogs inhibited NO production. Compounds 4 and 11 exhibited optimal activity with IC50 values of 0.3 and 0.5 µM, respectively, and were at least 38-fold better than the positive control. A mechanism of action study showed that both compounds significantly blocked the nuclear translocation of NF-κB p65 and up-regulation of iNOS at 1.0 µM. Compound 4 and three other analogs (3, 20, and 23) exerted significant in vitro anticancer activity GI50 values ranging from 0.70~13.10 µM. A mode of action study using HT-29 colon cancer cells showed that 23 acts by inducing apoptosis signaling.
bichalcone analogs; nitric oxide production inhibition; cytotoxicity; apoptosis
Epiceanothic acid (1) is a naturally occurring, but very rare pentacyclic triterpene with a unique pentacyclic triterpene (PT) structure. An efficient synthesis of 1 starting from betulin (3) has been accomplished in 12 steps with a total yield of 10% in our study. Compound 1 and selected synthetic intermediates were further evaluated as anti-HIV-1 agents, inhibitors of glycogen phosphorylase (GP), and cytotoxic agents. Compound 1 exhibited moderate HIV-1 inhibition. Most importantly, compound 5, with an opened A-ring, showed significant GP inhibitory activity with an IC50 of 0.21 μM, suggesting a potential for development as an anti-diabetic agent. On the other hand, compound 12, with a closed A-ring, showed potent cytotoxicity against A549 and MCF-7 human tumor cell lines, with IC50 values of 0.89 and 0.33 μM, respectively. These results suggest that the A-ring of PTs is an important pharmacophore that could be modified to involve different biological activities.
epiceanothic acid; pentacyclic triterpene; anti-HIV agents; glycogen phosphorylase inhibitors; cytotoxic agents
Five new benzenoids, benzocamphorins A–E (1–5), and ten recently isolated triterpenoids, camphoratins A–J (16–25), together with 23 known compounds including seven benzenoids (6–12), three lignans (13–15), and 13 triterpenoids (26–38) were isolated from the fruiting body of Taiwanofungus camphoratus. Their structures were established by spectroscopic analysis. Selected compounds were examined for cytotoxic and anti-inflammatory activities. Compounds 9 and 21 showed moderate cytotoxicity against MCF-7 and Hep2 cell lines with ED50 values of 3.4 and 3.0 µg/mL, respectively. Compounds 21, 25, 26, 29–31, 33, and 36 demonstrated potent anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced nitric oxide (NO) production with IC50 values of 2.5, 1.6, 3.6, 0.6, 4.1, 4.2, 2.5, and 1.5 µM, respectively, which were better than those of the nonspecific nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME) (IC50: 25.8 µM). These results may substantiate the use of T. camphoratus in traditional Chinese medicine (TCM) for the treatment of inflammation and cancer-related diseases. The newly discovered compounds deserve further development as anti-inflammatory candidates.
Taiwanofungus camphoratus; Fruiting bodies; Anti-inflammatory; NOX; ROS; Cytotoxicity
This article will review selected herbal products from Chinese Materia Medica that are used in Traditional Chinese Medicine. The herbs come from the upper, middle, and lower class medicines as listed in The Divine Husbandman's Herbal Foundation Canon (神農本草經 Shén Nóng Běn Cǎo Jīng). The review will focus on the active constituents of the herbs and their bioactivities, with emphasis on the most recent progress in research for the period of 2003 to 2011.
Herbal products; Chinese Materia Medica (CMM) (中藥 zhōng yào); Traditional Chinese Medicine (TCM); Shén Nóng Běn Cǎo Jīng (神農本草經 The Divine Husbandman's Herbal Foundation Canon by Shen Nong)
Ten new triterpenoids, camphoratins A–J (1–10), along with 12 known compounds were isolated from the fruiting body of Taiwanofungus camphoratus. Their structures were established by spectroscopic analysis and chemical methods. Compound 10 is the first example of a naturally occurring ergosteroid with an unusual cis-C/D ring junction. Compounds 2–6 and 11 showed moderate to potent cytotoxicity with EC50 values ranging from 0.3 to 3 μM against KB and KB-VIN human cancer cell lines. Compounds 6, 10, 11, 14–16, 18, and 21 exhibited anti-inflammatory NO-production inhibition activity with IC50 values of less than 5 μM, which was more potent than the nonspecific NOS inhibitor Nω-nitro-L-arginine methyl ester (L-NAME).