Discovery of berberine analogs as potent and highly selective p300/CBP HAT inhibitors.

The protein p300 is a positive regulator of cancer progression and is related to many human pathological conditions. To find effective p300/CBP HAT inhibitors, we screened an internal compound library and identified berberine as a lead compound. Next, we designed, synthesized, and screened a series of novel berberine analogs, and discovered that analog 5d was a potent and highly selective p300/CBP HAT inhibitor with IC50 values of 0.070 µM and 1.755 µM for p300 and CBP, respectively. Western blotting further proved that 5d specifically decreased H3K18Ac and interfere with the function of histone acetyltransferase. Although 5d had only a moderate inhibitory effect on the MDA-MB-231 cell line, 5d suppressed the growth of 4T1 tumor growth in mice with a tumor weight inhibition ratio (TWI) of 39.7%. Further, liposomes-encapsulated 5d increased its inhibition of tumor growth to 57.8 % TWI. In addition, 5d has no obvious toxicity to the main organ of mice and the pharmacokinetic study confirmed that 5d has good absorption properties in vivo.

Design, synthesis, and antitumor study of a series of novel 1-Oxa-4-azaspironenone derivatives.

A series of 1-oxa-4-azaspiro[4,5]deca-6,9-diene-3,8-dione derivatives containing structural fragments of conjugated dienone have been synthesized previously by our group, however the Michael addition reaction between conjugated dienone and nucleophilic groups in the body may generate harmful and adverse effects. To reduce harmful side effects, the authors started with p-aminophenol to make 1-oxo-4- azaspirodecanedione derivatives, then utilized the Michael addition and cyclopropanation to eliminate α, ß unsaturated olefinic bond and lower the Michael reactivity of the compounds in vivo for optimization. At the same time, heteroatoms are put into the molecules in order to improve the hydrophilicity of the molecules and the binding sites of the molecules and the target molecules, establishing the groundwork for improved antitumor activity. The majority of the compounds had moderate to potent activity against A549 human lung cancer cells, MDA-MB-231 breast cancer cells, and Hela human cervical cancer cells. Among them, the compound 6d showed the strongest effect on A549 cell line with IC50 of 0.26 µM; the compound 8d showed the strongest cytotoxicity on MDA-MB-231 cell line with IC50 of 0.10 µM; and the compound 6b showed the strongest activity on Hela cell line with IC50 of 0.18 µM.

Design, synthesis, and antitumor activity evaluation of novel acyl sulfonamide spirodienones.

Based on the promising results of benzenesulfonamide spirodienones as antineoplastic agents, we have designed and synthesized a series of novel acyl sulfonamides spirodienone for antineoplastic evaluation. Of these, compound 4a exhibited remarkable in vitro antiproliferative activity by arresting the cell cycle and inducing apoptosis of MDA-MB-231 cells. Acute toxicity study has demonstrated 4a at 100 mg/kg dose caused no obvious toxicity to the major organs of mice. Moreover, compound 4a suppressed the growth of murine 4T1 tumor in vivo. Preliminary enzyme assay showed that 4a was a potential MMP2 inhibitor for cancer therapy. In all, these results indicate that compound 4a may be a lead compound for the development of anticancer agents.

One-Pot Synthesis of Seven-Membered Heterocyclic Derivatives of Diazepines Involving Copper-Catalyzed Rearrangement Cascade Allyl-Amination.

A novel and efficient method has been proposed for the synthesis of 1,4-benzodiazepine-5-ones from o-nitrobenzoic N-allylamides by using molybdenyl acetylacetonate and copper(II) trifluoromethanesulfonate as catalysts in the presence of triphenylphosphine. This synthesis process involves nitrene formation, C-H bond insertion, C═C bond rearrangement, and C-N bond formation cascade reactions via copper- and molybdenum-catalyzed mediation. The method features a wide substrate scope and a moderate to high yield (up to 90%), exhibiting the possibility for practical applications.

Development of a bioavailable boron-containing PI-103 Bioisostere, PI-103BE.

PI-103 (7) is a potent dual phosphatidylinositol 3-kinase (PI3K)/mTOR inhibitor, but its rapid in vivo metabolism hinders its further clinical development. To improve the bioavailability of PI-103, we designed and synthesized a PI-103 bioisostere, PI-103BE (9) in which the phenolic hydroxyl group of PI-103 was replaced by a boronate, a structural modification known to enhance bioavailability of molecules containing phenolic hydroxyl moieties. In cell culture, PI-103BE is partially converted to its corresponding boronic acid (10) and to a lesser extent the active ingredient, PI-103. This mixture contributes to the in vitro activity of 9 that shows reduced potency compared to the parent compound. When administered to mice by oral gavage, 9 displays a significantly improved pharmacokinetic profile compared to PI-103, which shows no oral bioavailability at the same dose. Drug exposure of 9 as measured by the area under curve (AUC) value is 88.2 ng/mL*h for 7 and 8879.9 ng/mL*h for 10. When given by intraperitoneal injection (IP), the prodrug afforded an AUC of 32.3 ng/mL*h for 7 and 400.9 ng/mL*h for 10, compared to 9.7 ng/mL*h from PI-103 injection. In plasma from both pharmacokinetic studies, 9 is fully converted to 10 and 7, with the boronic acid metabolite (10) displaying antiproliferative activities comparable to 9, but weaker than 7. The boronic bioisostere of PI-103 thus offers an improved bioavailability that could be translated to in vivo efficacy of PI-103.

Novel one-pot synthesis of imidazolinones from esters: a concise synthesis of GSK2137305.

A new copper-catalyzed one-pot reaction resulted in the practical synthesis of imidazolinones in moderate yields from esters. The use of inexpensive copper iodide as the catalyst, (NH4)2CO3 as the nitrogen source and readily available starting materials makes this process economically viable. Applying this protocol to the synthesis of GSK2137305, a concise approach was developed to obtain GSK2137305 from the ester in only three steps with an overall yield of 26.9%.

Design, Synthesis, and Antitumor Activity of a Series of Novel 4-(Aromatic Sulfonyl)-1-oxa-4-azaspiro[4.5]deca-6,9-dien-8-ones.

Many sulfonamides show anticancer activity. Based on benzenesulfonylazaspirodienone (HL-X9) identified in our previous work, we optimized the lead compound for better efficacy, thereby synthesizing a series of novel 4-(aromatic sulfonyl)-1-oxa-4-azaspiro[4.5]deca-6,9-dien-8-one derivatives through a key step of metal-catalyzed cascade cyclization. The preliminary antiproliferative tests have shown that the anticancer activities of acetyl-protected mannose-linked sulfonylazaspirodienone derivatives (7i-7l) have been greatly improved. Among them, 7j is the most potent derivative, with IC50 values of 0.17 µM, 0.05 µM, and 0.07 µM for A549, MDA-MB-231, and HeLa cell lines, respectively. Flow cytometry analysis shows that 7j arrests MDA-MB-231 cells in the G2/M phase and has a certain effect on the apoptosis of MDA-MB-231 cells. In addition, the acute toxicity of 7j was lower than that of adriamycin.

Synthesis and antiproliferative evaluation of new zampanolide mimics.

(-)-Zampanolide is a marine microtubule-stabilizing macrolide that has been shown by in vitro experiments to be a promising anticancer lead compound. Through its unique covalent-binding with ß-tubulin, zampanolide exhibits cytotoxic potency towards multi-drug resistant cancer cells that is superior to paclitaxel. However, the limited availability of zampanolide impedes its further in vivo evaluation as a viable drug candidate. Zampanolide is envisioned to become more drug-like if its chemically fragile side chain can be stabilized; hence, this project aims to develop mimics of zampanolide with a stable side chain using straightforward synthetic methods. To this end, twelve novel zampanolide mimics (51-62) with conjugated and planar side chains have been synthesized via a 24-step sequence for each mimic from commercially available 2-butyn-1-ol as starting material. A Horner-Wadsworth-Emmons reaction incorporates the α,ß-unsaturated ketone side chain and also closes the core macrocycle. WST-1 cell proliferation assays in three docetaxel-sensitive and two docetaxel-resistant human prostate cancer cell models confirm that a suitably designed side chain can serve as a bioisostere for the N-acyl hemiaminal side chain in zampanolide. Mimic 52 with a 17R chiral center was identified as the optimal candidate with IC50 values of 0.29-0.46 µM against both docetaxel-sensitive (PC-3 and DU145) and docetaxel-resistant prostate cancer cell lines (PC-3/DTX and DU145/DTX). Zampanolide mimic 52 exhibited equivalent antiproliferative potency towards both docetaxel-sensitive and docetaxel-resistant cell lines, with relative resistance in the range of 0.9-1.6.

Nitrogen-containing derivatives of O-tetramethylquercetin: Synthesis and biological profiles in prostate cancer cell models.

Forty-eight nitrogen-containing quercetin derivatives were synthesized from readily available rutin or quercetin for the in vitro evaluation of their biological profiles. The WST-1 cell proliferation assay data indicate that thirty-nine out of the forty-eight derivatives possess significantly improved antiproliferative potency as compared with quercetin and fisetin, as well as the parent 3,3',4',7-O-tetramethylquercetin toward both androgen-sensitive (LNCaP) and androgen-insensitive (PC-3 and DU145) human prostate cancer cell lines. 5-O-Aminoalkyl-3,3',4',7-O-tetramethylquercetins were established as a better scaffold for further development as anti-prostate cancer agents. Among them, 5-O-(N,N-dibutylamino)propyl-3,3',4',7-O-tetramethylquercetin (44) was identified as the optimal derivative with IC50 values of 0.55-2.82 µM, being over 35-182 times more potent than quercetin. The flow cytometry-based assays further demonstrate that 44 effectively activates PC-3 cell apoptosis.

Synthesis and Antitumor Activity of a Series of Novel 1-Oxa-4-azaspiro[4,5]deca-6,9-diene-3,8-dione Derivatives.

A series of novel 1-oxa-4-azaspiro[4.5]deca-6,9-diene-3,8-diones were designed and synthesized by using 4-aminophenol and α-glycolic acid or lactic acid as starting materials in three or four steps. The key step is the metal-catalyzed oxidative cyclization of the amide to 1-oxa-4-azaspiro[4.5]deca-6,9-diene-3,8-diones (10a and 10b), the reaction conditions of which are investigated and optimized. The anticancer activity of 17 1-oxa-4-azaspiro[4.5]deca-6,9-diene-3,8-dione derivatives was evaluated. Preliminary results showed that 15 compounds have moderate to potent activity against human lung cancer A549, human breast cancer MDA-MB-231, and human cervical cancer HeLa cancer cell lines. Among them, compounds 11b and 11h were the most potent against A549 cell line with 0.18 and 0.19 µM of IC50, respectively; compounds 11d, 11h, and 11k showed the most potent cytotoxicity against MDA-MB-231 cell line with 0.08, 0.08, and 0.09 µM of IC50, respectively, while the activities of 11h, 11k, and 12c against HeLa cell line were the most potent with 0.15, 0.14, and 0.14 µM of IC50, respectively. Compound 11h is a promising candidate for further development, which emerged as the most effective compound overall against the three tested cancer cell lines.

Optimization of diarylpentadienones as chemotherapeutics for prostate cancer.

Our earlier studies indicate that (1E,4E)-1,5-bis(1-alkyl-1H-imidazol-2-yl)penta-1,4-diene-3-ones and (1E,4E)-1,5-bis(1-alkyl-1H-benzo[d]imidazol-2-yl)penta-1,4-diene-3-ones exhibit up to 121-fold greater antiproliferative potency than curcumin in human prostate cancer cell models, but only 2-10 fold increase in mouse plasma concentrations. The present study aims to further optimize them as anti-prostate cancer agents with both good potency and bioavailability. (1E,4E)-1,5-Bis(1H-imidazol-2-yl)penta-1,4-diene-3-one, the potential metabolic product of (1E,4E)-1,5-bis(1-alkyl-1H-imidazol-2-yl)penta-1,4-diene-3-ones, was synthesized and evaluated for its anti-proliferative activity. The promising potency of 1,5-bis(1-alkyl-1H-imidazol-2-yl)penta-1,4-diene-3-ones was completely abolished by removing the 1-alkyl group, suggesting the critical role of an appropriate group on the N1 position. We then envisioned that N-aryl substitution to exclude the C-H bond on the carbon adjacent to the N1 position (α-H) may increase the metabolic stability. Consequently, seven (1E,4E)-1,5-bis(1-aryl-1H-imidazol-2-yl)penta-1,4-dien-3-ones and three (1E,4E)-1,5-bis(1-aryl-1H-benzo[d]imidazol-2-yl)penta-1,4-dien-3-ones, as well as three (1E,4E)-1,5-bis(1-aryl-1H-pyrrolo[3,2-b]pyridine-2-yl)penta-1,4-dien-3-ones, were synthesized through a three-step transformation, including N-arylation via Ullmann condensation, formylation, and Horner-Wadsworth-Emmons reaction. Six optimal (1E,4E)-1,5-bis(1-aryl-1H-imidazol-2-yl)penta-1,4-dien-3-ones exhibit 24- to 375-fold improved potency as compared with curcumin. Replacement of the imidazole with bulkier benzoimidazole and 4-azaindole results in a substantial decrease in the potency. (1E,4E)-1,5-Bis(1-(2-methoxyphenyl)-1H-imidazol-2-yl)penta-1,4-dien-3-one (17d) was established as an optimal compound with both superior potency and good bioavailability that is sufficient to provide the therapeutic efficacy necessary to suppress in vivo tumor growth.

Optimized synthesis and antiproliferative activity of desTHPdactylolides.

Dactylolide and certain analogues are attractive targets for study due to their structural resemblance to zampanolide, a very promising anticancer lead compound and a unique covalent-binding microtubule stabilizing agent. The primary goal of this project is identification and synthesis of simplified analogues of dactylolide that would be easier to prepare and could be investigated for antiproliferative activity in comparison with zampanolide. Extension of Almann's concept of a simplified zampanolide analogue to dactylolide in the form of desTHPdactylolide was attractive not only for reasons of synthetic simplification but also for the prospect that analogues of dactylolide could be prepared in both (17S) and (17R) configurations. Since Altmann's overall yield for the six-step procedure leading to the C9-C18 fragment of desTHPdactylolide was only 8.7%, a study focused on optimized synthesis and antiproliferative evaluation of each enantiomer of desTHPdactylolide was initiated using Altmann's route as a framework. To this end, two optimized approaches to this fragment C9-C18 were successfully developed by us using allyl iodide or allyl tosylate as the starting material for a critical Williamson ether synthesis. Both (17S) and (17R) desTHPdactylolides were readily synthesized in our laboratory using optimized methods in yields of 37-43%. Antiproliferative activity of the pair of enantiomeric desTHPdactylolides, together with their analogues, was evaluated in three docetaxel-sensitive and two docetaxel-resistant prostate cancer cell models using a WST-1 cell proliferation assay. Surprisingly, (17R) desTHPdactylolide was identified as the eutomer in the prostate cancer cell models. It was found that (17S) and (17R) desTHPdactylolide exhibit equivalent antiproliferative potency towards both docetaxel-sensitive (PC-3 and DU145) and docetaxel-resistant prostate cancer cell lines (PC-3/DTX and DU145/DTX).

O-Aminoalkyl-O-Trimethyl-2,3-Dehydrosilybins: Synthesis and In Vitro Effects Towards Prostate Cancer Cells.

As part of our ongoing silybin project, this study aims to introduce a basic nitrogen-containing group to 7-OH of 3,5,20-O-trimethyl-2,3-dehydrosilybin or 3-OH of 5,7,20-O-trimethyl-2,3-dehydrosilybin via an appropriate linker for in vitro evaluation as potential anti-prostate cancer agents. The synthetic approaches to 7-O-substituted-3,5,20-O-trimethyl-2,3-dehydrosilybins through a five-step procedure and to 3-O-substituted-5,7,20-O-trimethyl-2,3- dehydrosilybins via a four-step transformation have been developed. Thirty-two nitrogen-containing derivatives of silybin have been achieved through these synthetic methods for the evaluation of their antiproliferative activities towards both androgen-sensitive (LNCaP) and androgen-insensitive prostate cancer cell lines (PC-3 and DU145) using the WST-1 cell proliferation assay. These derivatives exhibited greater in vitro antiproliferative potency than silibinin. Among them, 11, 29, 31, 37, and 40 were identified as five optimal derivatives with IC50 values in the range of 1.40⁻3.06 µM, representing a 17- to 52-fold improvement in potency compared to silibinin. All these five optimal derivatives can arrest the PC-3 cell cycle in the G0/G1 phase and promote PC-3 cell apoptosis. Derivatives 11, 37, and 40 are more effective than 29 and 31 in activating PC-3 cell apoptosis.

3-O-Substituted-3',4',5'-trimethoxyflavonols: Synthesis and cell-based evaluation as anti-prostate cancer agents.

Twenty-two 3-O-substituted-3',4',5'-trimethoxyflavonols have been designed and synthesized for their anti-proliferative activity towards three human prostate cancer cell lines. Our results indicate that most of them are significantly more potent than the parent 3',4',5'-trimethoxyflavonol in inhibiting the cell proliferation in PC-3 and LNCaP prostate cancer cell models. 3-O-Substituted-3',4',5'-trimethoxyflavonols have generally higher potency towards PC-3 and LNCaP cell lines than the DU145 cell line. Incorporation of an ethyl group to 3-OH of 3',4',5'-trimethoxyflavonol leads to 3-O-ethyl-3',4',5'-trimethoxyflavonol as the optimal derivative with up to 36-fold enhanced potency as compared with the corresponding lead compound 3',4',5'-trimethoxyflavonol, but with reversed PC-3 cell apoptotic response. Introduction of a dipentylaminopropyl group to 3-OH increases not only the antiproliferative potency but also the ability in activating PC-3 cell apoptosis. Our findings imply that modification on 3-OH of trimethoxyflavonol can further enhance its in vitro anti-proliferative potency and PC-3 cell apoptosis induction.

5- or/and 20-O-alkyl-2,3-dehydrosilybins: Synthesis and biological profiles on prostate cancer cell models.

To investigate the effects of alkylation at 5-OH and 20-OH of 2,3-dehydrosilybin on prostate cancer cell proliferation, the synthetic approaches to 5- or/and 20-O-alkyl-2,3-dehydrosilybins, through a multi-step sequence from commercially available silybin, have been successfully developed. The first three reactions in the syntheses were completed through a one-pot procedure by managing anaerobic and aerobic conditions. With these synthetic methods in hand, twenty-one 2,3-dehydrosilybins, including seven 20-O-alkyl, seven 5,20-O-dialkyl, and seven 5-O-alkyl-2,3-dehydrosilybins, have been achieved for the evaluation of their biological profiles. Our WST-1 cell proliferation assay data indicate that nineteen out of the twenty-one 2,3-dehydrosilybins possess significantly improved antiproliferative potency as compared with silybin toward both androgen-sensitive (LNCaP) and androgen-insensitive prostate cancer cell lines (PC-3 and DU145). 5-O-Alkyl-2,3-dehydrosilybins were identified as the optimal subgroup that can consistently inhibit cell proliferation in three prostate cancer cell models with all IC50 values lower than 8µM. Our flow cytometry-based assays also demonstrate that 5-O-heptyl-2,3-dehydrosilybin effectively arrests the cell cycle in the G0/G1 phase and activates PC-3 cell apoptosis.

Ligands of Therapeutic Utility for the Liver X Receptors.

Liver X receptors (LXRs) have been increasingly recognized as a potential therapeutic target to treat pathological conditions ranging from vascular and metabolic diseases, neurological degeneration, to cancers that are driven by lipid metabolism. Amidst intensifying efforts to discover ligands that act through LXRs to achieve the sought-after pharmacological outcomes, several lead compounds are already being tested in clinical trials for a variety of disease interventions. While more potent and selective LXR ligands continue to emerge from screening of small molecule libraries, rational design, and empirical medicinal chemistry approaches, challenges remain in minimizing undesirable effects of LXR activation on lipid metabolism. This review provides a summary of known endogenous, naturally occurring, and synthetic ligands. The review also offers considerations from a molecular modeling perspective with which to design more specific LXRß ligands based on the interaction energies of ligands and the important amino acid residues in the LXRß ligand binding domain.

A new class of flavonol-based anti-prostate cancer agents: Design, synthesis, and evaluation in cell models.

Flavonoids are a large class of polyphenolic compounds ubiquitously distributed in dietary plants with an array of biological activities. Flavonols are a major sub-class of flavonoids featuring a hydroxyl group at C-3. Certain natural flavonols, such as quercetin and fisetin, have been shown by in vitro cell-based and in vivo animal experiments to be potential anti-prostate cancer agents. However, the Achilles' heel of flavonols as drug candidates is their moderate potency and poor pharmacokinetic profiles. This study aims to explore the substitution effect of 3-OH in flavonols on the in vitro anti-proliferative potency against both androgen-sensitive and androgen-insensitive human prostate cancer cell lines. Our first lead flavonol (3',4'-dimethoxyflavonol), eight 3-O-alkyl-3',4'-dimethoxyflavonols, and six 3-O-aminoalkyl-3',4'-dimethoxyflavonols have been synthesized through aldol condensation and the Algar-Flynn-Oyamada (AFO) reaction. The WST-1 cell proliferation assay indicates (i) that all synthesized 3-O-alkyl-3',4'-dimethoxyflavonols and 3-O-aminoalkyl-3',4'-dimethoxyflavonols are more potent than the parent 3',4'-dimethoxyflavonol and the natural flavonol quercetin in suppressing prostate cancer cell proliferation; and (ii) that incorporation of a dibutylamino group to the 3-OH group through a three- to five-carbon linker leads to the optimal derivatives with up to 292-fold enhanced potency as compared with the parent flavonol. Flow cytometry analysis showed that the most potent derivative 22 can activate PC-3 cell cycle arrest at the G2/M phase and induce PC-3 cell apoptosis. No inhibitory ability of 22 up to 50µM concentration was observed against PWR-1E normal human epithelial prostate cells, suggesting its in vitro safety profile. The results indicate that chemical modulation at 3-OH is a vital strategy to optimize flavonols as anti-prostate cancer agents.

3-O-Alkyl-2,3-dehydrosilibinins: Two synthetic approaches and in vitro effects toward prostate cancer cells.

Eight 3-O-alkyl-2,3-dehydrosilibinins have been synthesized from commercially available silibinin through two synthetic approaches. A one-pot reaction, starting with aerobic oxidation of silibinin followed by direct alkylation of the phenolic hydroxyl group in the subsequent 2,3-dehydrosilibinin, furnishes the desired derivatives in 11-16% yields. The three-step procedure employing benzyl ether to protect 7-OH in silibinin generates the desired derivatives in 30-46% overall yields. The antiproliferative activity of the 2,3-dehydrosilibinin derivatives against both androgen-sensitive and androgen-insensitive prostate cancer cells have been assessed using a WST-1 cell proliferation assay. All derivatives exhibited greater antiproliferative potency than silibinin, with 2,3-dehydrosilibinins each possessing a three- to five-carbon linear alkyl group to 3-OH (IC50 values in a range of 1.71-3.06µM against PC-3 and LNCaP cells) as the optimal derivatives. The optimal potency was reached with three- to five-carbon alkyl groups. Our findings suggest that 3-O-propyl-2,3-dehydrosilibinin effectively inhibits the growth of PC-3 prostate cancer cells by arresting cell cycle in the G0/G1 phase, but not by activating PC-3 cell apoptosis.

Design, synthesis, and biological evaluation of 1,9-diheteroarylnona-1,3,6,8-tetraen-5-ones as a new class of anti-prostate cancer agents.

In search of more effective chemotherapeutics for the treatment of castration-resistant prostate cancer and inspired by curcumin analogues, twenty five (1E,3E,6E,8E)-1,9-diarylnona-1,3,6,8-tetraen-5-ones bearing two identical terminal heteroaromatic rings have been successfully synthesized through Wittig reaction followed by Horner-Wadsworth-Emmons reaction. Twenty-three of them are new compounds. The WST-1 cell proliferation assay was employed to assess their anti-proliferative effects toward both androgen-sensitive and androgen-insensitive human prostate cancer cell lines. Eighteen out of twenty-five synthesized compounds possess significantly improved potency as compared with curcumin. The optimal compound, 78, is 14- to 23-fold more potent than curcumin in inhibiting prostate cancer cell proliferation. It can be concluded from our data that 1,9-diarylnona-1,3,6,8-tetraen-5-one can serve as a new potential scaffold for the development of anti-prostate cancer agents and that pyridine-4-yls and quinolin-4-yl act as optimal heteroaromatic rings for the enhanced potency of this scaffold. Two of the most potent compounds, 68 and 75, effectively suppress PC-3 cell proliferation by activating cell apoptosis and by arresting cell cycle in the G0/G1 phase.

Discovery of Novel Allopurinol Derivatives with Anticancer Activity and Attenuated Xanthine Oxidase Inhibition.

A series of pyrazolo[3,4-d]pyrimidine derivatives related to allopurinol has been synthesized and evaluated for its cytotoxicity against a panel of three cancer cell lines as well as its xanthine oxidase (XOD) inhibitory activities. Among them, compound 4 showed potent cytotoxicity with IC50 values of 25.5 and 35.2 µM against human hepatoma carcinoma cell lines, BEL-7402 and SMMC-7221, respectively. The anticancer activity of 4 was comparable to that of Tanespimycin (17-N-allylamino-17-demethoxy geldanamycin, 17-AAG) that inhibited the growth of BEL-7402 and SMMC-7221 cells at IC50 values of 12.4 and 9.85 µM, respectively. However, unlike allopurinol, which is also a strong inhibitor of XOD, compound 4 is a much weaker XOD inhibitor, suggesting that the anticancer activities of the allopurinol derivatives may not be associated with XOD inhibition. Moreover, the cytotoxicity of 4 toward normal cells is significantly lower than that of 17-AAG, making 4 a promising lead compound for further optimization of structure-activity relationships that may lead to anticancer agents of clinical utility.