Flavonoid dimer FD18 is a new class of dimeric P-gp modulator that can reverse cancer drug resistance. FD18 is a potent (EC50 = 148 nM for paclitaxel), safe (selective index = 574), and selective P-glycoprotein (P-gp) modulator. FD18 can modulate multidrug resistance toward paclitaxel, vinblastine, vincristine, doxorubicin, daunorubicin, and mitoxantrone in human breast cancer LCC6MDR in vitro. FD18 (1 μM) can revert chemosensitivity of LCC6MDR back to parental LCC6 level. FD18 was 11- to 46-fold more potent than verapamil. FD18 (1 μM) can increase accumulation of doxorubicin by 2.7-fold, daunorubicin (2.1-fold), and rhodamine 123 (5.2-fold) in LCC6MDR. FD18 inhibited P-gp-mediated doxorubicin efflux and has no effect on influx. FD18 at 1 μM did not affect the protein expression level of P-gp. Pharmacokinetics studies indicated that intraperitoneal administration of 45 mg/kg FD18 was enough to maintain a plasma level above EC50 (148 nM) for more than 600 min. Toxicity studies with FD18 (90 mg/kg, i.p. for 12 times in 22 days) with paclitaxel (12 mg/kg, i.v. for 12 times in 22 days) revealed no obvious toxicity or death in mice. In vivo efficacy studies indicated that FD18 (45 mg/kg, i.p. for 12 times in 22 days) together with paclitaxel (12 mg/kg, i.v. for 12 times in 22 days) resulted in a 46% reduction in LCC6MDR xenograft volume (n = 11; 648 ± 84 mm3) compared to paclitaxel control (n = 8; 1201 ± 118 mm3). There were no animal deaths or significant drop in body weight and vital organ wet weight. FD18 can increase paclitaxel accumulation in LCC6MDR xenograft by 1.8- to 2.2-fold. The present study suggests that FD18 represents a new class of safe and potent P-gp modulator in vivo.

The present study found that synthetic flavonoid dimers with either polyethylene glycol linker or amino ethyleneglycol linker have marked leishmanicidal activity. Compound 39 showed very consistent and promising leishmanicidal activity for both extracellular promastigotes (IC50 ranging from 0.13 to 0.21 μM) and intracellular amastigotes (IC50 = 0.63 μM) irrespective of the drug-sensitivity of parasites. Moreover, compound 39 displayed no toxicity toward macrophage RAW 264.7 cells (IC50 > 100 μM) and primary mouse peritoneal elicited macrophages (IC50 > 88 μM). Its high value of therapeutic index (>140) was better than other highly potent antileishmanials such as amphotericin B (therapeutic index = 119). Compound 39 is therefore a new, safe, and effective antileishmanial candidate compound which is even effective against drug-refractory parasites.

Here we report a great improvement in reversal potency of cancer drug resistance when flavonoid dimers possess a functionally substituted aminopolyethylene glycol linker. The most potent compound, 18, contains a N-benzyl group at the linker. It has many advantages including (1) high potencies in reversing P-glycoprotein (P-gp) mediated resistance in LCC6MDR cells to various anticancer drugs with EC50 in the nanomolar range, (2) low toxicity and high therapeutic index, and (3) preferential inhibition of P-gp over multidrug resistance protein 1 and breast cancer resistance protein. Compound 18 stimulates P-gp-ATPase activity by 2.7-fold and mediates a dose-dependent inhibition of doxorubicin (DOX) transport activity. Lineweaver–Burk and Dixon plots suggest that 18 is a competitive inhibitor to DOX in binding to P-gp with a Ki of 0.28–0.34 μM and a Hill coefficient of 1.17. Moreover, the LCC6MDR cell displays about 2.1-fold lower intracellular accumulation of 18 compared to the wild type, suggesting that 18 is a P-gp substrate as well.

EGCG analogs 6 and 8 with 1,3-benzenediol, but not 2 and 4 with a 1,2-benzenediol structure, can enhance the anti-cancer effects of bortezomib (BZM) on human multiple myeloma cells.

A pro-drug 8 of a synthetic analog 7 is more active in its antiproliferative activity against human breast cancer MDA-MB-231 cells possessing high catechol-O-methyltransferase (COMT) activity than the pro-drugs of EGCG and the analog 5. The higher activity of 8 is attributed to it not being a substrate of COMT.

Here we showed that bivalency approach is effective in modulating multidrug resistance protein 1 (MRP1/ABCC1)-mediated doxorubicin (DOX) and etoposide (VP16) resistance in human 2008/MRP1 ovarian carcinoma cells. Flavonoid dimers bearing five or six ethylene glycol (EG) units with 6-methyl (4e, 4f) or 7-methyl (5e, 5f) substitution on the ring A of flavonoid dimers have the highest modulating activity for DOX against MRP1 with an EC50 ranging from 73 to 133 nM. At 0.5 μM, the flavonoid dimer 4e was sufficient to restore DOX accumulation in 2008/MRP1 to parental 2008/P level. Lineweaver−Burk and Dixon plot suggested that it is likely a competitive inhibitor of DOX transport with a Ki = 0.2 μM. Our data suggest that flavonoid dimers have a high affinity toward binding to DOX recognition site of MRP1. This results in inhibiting DOX transport, increasing intracellular DOX retention, and finally resensitizing 2008/MRP1 to DOX. The present study demonstrates that flavonoid dimers can be employed as an effective modulator of MRP1-mediated drug resistance in cancer cells.

The health benefits of green tea and its main constituent (-)-epigallocatechin gallate [(-)-EGCG] have been widely supported by results from epidemiological, cell culture, animal and clinical studies. On the other hand, there are a number of issues, such as stability, bioavailability and metabolic transformations under physiological conditions, facing the development of green tea polyphenols into therapeutic agents. We previously reported that the synthetic peracetate of (-)-EGCG has improved stability and better bioavailability than (-)-EGCG itself and can act as pro-drug under both in vitro and in vivo conditions. Analogs of catechins have been synthesized and their structure activity relationship provides an understanding to the mechanism of proteasome inhibition. Metabolic methylation of catechins leading to methylated (-)-EGCG may alter the biological activities of these compounds.

Analogs of (−)-EGCG containing a para-amino group on the D-ring in place of the hydroxyl groups have been synthesized and their proteasome inhibitory activities were studied. We found that, the O-acetylated (−)-EGCG analogs possessing a p-NH2 or p-NHBoc (Boc; tert-butoxycarbonyl) D-ring (5 and 7) act as novel tumor cellular proteasome inhibitors and apoptosis inducers with potency similar to natural (−)-EGCG and similar to (−)-EGCG peracetate. These data suggest that the acetylated amino-GTP analogs have the potential to be developed into novel anticancer agents.

Grignard reagents were generated from magnesium and organic iodides in the ionic liquid n-butylpyridinium tetrafluoroborate, [bpy][BF4], and they showed different reactivity from classical Grignard reagents in organic solvents.

Hydrogen peroxide can be electrosynthesized from oxygen in [bmim][BF4]–water and used in situ for the epoxidation of alkenes.

The structure–activity relationship of a number of synthetic green tea polyphenol analogs involving modifications of A ring and B ring of epi-gallocatechin gallate (EGCG) as proteasome inhibitors has been examined. It was found that in B ring, a decrease in the number of OH groups led to decreased potency. Introduction of a hydrophobic benzyl group into the 8 position of A ring did not significantly affect the proteasome-inhibitory potency.

The ionic liquids, [bmim][Br] (2a), [bmim][BF4] (2b), [bmim][PF6] (2c), [bdmim][BF4] (8) and [bpy][BF4] (9), were examined as the solvent media for dialkylzinc addition to aldehydes giving the corresponding alcohols. The ionic liquid [bpy][BF4] was found to be the solvent of choice, giving the best yields, easily recovered and reused.

Green tea has been shown to have many biological effects, including effects on metabolism, angiogenesis, oxidation, and cell proliferation. Unfortunately, the most abundant green tea polyphenol (−)-epigallocatechin gallate or (−)-EGCG is very unstable in neutral or alkaline medium. This instability leads to a low bioavailability. In an attempt to enhance the stability of (−)-EGCG, we introduced peracetate protection groups on the reactive hydroxyls of (−)-EGCG (noted in text as 1). HPLC analysis shows that the protected (−)-EGCG analog is six times more stable than natural (−)-EGCG under slightly alkaline conditions. A series of bioassays show that 1 has no inhibitory activity against a purified 20S proteasome in vitro, but exhibits increased proteasome-inhibitory activity in intact leukemic cells over natural (−)-EGCG, indicating an intercellular conversion. Inhibition of cellular proteasome activity by 1 is associated with induction of cell death. Therefore, our results indicate that the protected analog 1 may function as a prodrug of the green tea polyphenol proteasome inhibitor (−)-EGCG.

The green tea polyphenol catechin-3-gallate (CG) and epicatechin-3-gallate (ECG) were synthesized enantioselectively via a Sharpless hydroxylation reaction followed by a diastereoselective cyclization. Their potencies to inhibit the proteasome activity were measured. The unnatural enantiomers were found to be equally potent to the natural compounds.Graphic

Water moderation has been used for solvent-free microwave assisted reactions which generate over-heating. The method is demonstrated by the large scale preparation of ionic liquid precursors.

In, Sn and Zn metals mediate the allylation of carbonyl compounds in [bmim][BF4] or [emim][BF4] to give the corresponding homoallylic alcohols in good to excellent yields. Tin was found to be the metal of choice among the metals examined.