Chien-Shu Chen

Benzyl Ether-Linked Glucuronide Derivative of 10-Hydroxycamptothecin Designed for Selective Camptothecin-Based Anticancer Therapy

A beta-glucuronidase-activated prodrug approach was applied to 10-hydroxycamptothecin, a Camptotheca alkaloid with promising antitumor activity but poor water solubility. We synthesized a glucuronide prodrug of 10-hydroxycamptothecin ( 7) in which glucuronic acid is connected via a self-immolative 3-nitrobenzyl ether linker to the 10-OH group of 10-hydroxycamptothecin. Compound 7 was 80 times more soluble than 10-hydroxycamptothecin in aqueous solution at pH 4.0 and was stable in human plasma. Prodrug 7 was 10- to 15-fold less toxic than the parent drug to four human tumor cell lines. In the presence of beta-glucuronidase, prodrug 7 could be activated to elicit similar cytotoxicity to the parent drug in tumor cells. Enzyme kinetic studies showed that Escherichia coli beta-glucuronidase had a quite low K m of 0.18 microM for compound 7 and exhibited 520 times higher catalytic efficiency for 7 than for 6 (a glucuronide prodrug of 9-aminocamptothecin). Molecular modeling studies predicted that compound 7 would have a higher binding affinity to human beta-glucuronidase than compound 6. Prodrug 7 may be useful for selective cancer chemotherapy by a prodrug monotherapy (PMT) or antibody-directed enzyme prodrug therapy (ADEPT) strategy.

Structure-based discovery of triphenylmethane derivatives as inhibitors of hepatitis C virus helicase.

Hepatitis C virus nonstructural protein 3 (HCV NS3) helicase is believed to be essential for viral replication and has become an attractive target for the development of antiviral drugs. A fluorescence resonant energy transfer helicase assay was established for fast screening of putative inhibitors selected from virtual screening using the program DOCK. Soluble blue HT (1) was first identified as a novel HCV helicase inhibitor. Crystal structure of the NS3 helicase in complex with soluble blue HT shows that the inhibitor bears a significantly higher binding affinity mainly through a 4-sulfonatophenylaminophenyl group, and this is consistent with the activity assay. Subsequently, fragment-based searches were utilized to identify triphenylmethane derivatives for more potent inhibitors. Lead optimization resulted in a 3-bromo-4-hydroxyl substituted derivative 12 with an EC(50) value of 2.72 microM to Ava.5/Huh-7 cells and a lower cytotoxicity to parental Huh-7 cells (CC(50) = 10.5 microM), and it indeed suppressed HCV replication in the HCV replicon cells. Therefore, these inhibitors with structural novelty may serve as a useful scaffold for the discovery of new HCV NS3 helicase inhibitors.

Studies on 1,2,4-benzothiadiazine 1,1-dioxides VII1 and quinazolinones IV2: synthesis of novel built-in hydroxyguanidine tricycles as potential anticancer agents

Two representative built-in hydroxyguanidine tricycles containing 1,2,4-benzothiadiazine 1,1-dioxides (3) and quinazolinones (4) were prepared by reductive cyclization of 1-(2-nitrophenylsulfonyl)-2-benzylthio-2-imidazoline (9a), 1-(2-nitrophenylsulfonyl)-2-benzylthio-1,4,5,6-tetrahydropyrimidine (9b), 1-(2-nitrobenzoyl)-2-benzylthio-2-imidazolidine (10a) and 1-(2-nitrobenzoyl)-2-benzylthio-1,4,5,6-tetrahydropyrimidine hydrobromide respectively (10b) with zinc dust in acetic acid under ice-cooling. 2,10-Dihydro-10-hydroxy-3H-imidazo[1,2-b][1,2,4]benzothiadiazine 5,5-dioxide (3a) and 2,3,4,11-tetrahydro-11-hydroxypyrimido[1,2-b][1,2,4]benzothiadiazine 6,6-dioxide (3b) were found to be active against solid tumor cell lines such as KB, Colo 205, HeLa, and Hepa-2

Discovery of 3-(4-bromophenyl)-6-nitrobenzo[1.3.2]dithiazolium ylide 1,1-dioxide as a novel dual cyclooxygenase/5-lipoxygenase inhibitor that also inhibits tumor necrosis factor-α production

In the present study we have discovered compound 1, a benzo[1.3.2]dithiazolium ylide-based compound, as a new prototype dual inhibitor of cyclooxygenase (COX) and 5-lipoxygenase (5-LOX). Compound 1 was initially discovered as a COX-2 inhibitor, resulting indirectly from the COX-2 structure-based virtual screening that identified compound 2 as a virtual hit. Compounds 1 and 2 inhibited COX-1 and COX-2 in mouse macrophages with IC(50) in the range of 1.5-18.1microM. Both compounds 1 and 2 were also found to be potent inhibitors of human 5-LOX (IC(50)=1.22 and 0.47microM, respectively). Interestingly, compound 1 also had an inhibitory effect on tumor necrosis factor-alpha (TNF-alpha) production (IC(50)=0.44microM), which was not observed with compound 2. Docking studies suggested the (S)-enantiomer of 1 as the biologically active isomer that binds to COX-2. Being a cytokine-suppressive dual COX/5-LOX inhibitor, compound 1 may represent a useful lead structure for the development of advantageous new anti-inflammatory agents.

Design, synthesis and biological evaluation of benzo[1.3.2]dithiazolium ylide 1,1-dioxide derivatives as potential dual cyclooxygenase-2/5-lipoxygenase inhibitors.

3-(4-Bromophenyl)-6-nitrobenzo[1.3.2]dithiazolium ylide 1,1-dioxide (5) was discovered as a new prototype for dual inhibitors of cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX). Thus, the structure-activity relationships of benzo[1.3.2]dithiazolium ylide 1,1-dioxide skeleton were carried out. The 6-NO(2) group played an essential role in the inhibitory activity. In addition, moderate-sized lipophilic substituents at the para-position of the 3-aryl moiety were required for dual COX-2/5-LOX inhibitory activity. Among the identified potent dual inhibitors, 3-(4-tbutylphenyl) derivative 30c (IC(50) values of 0.27 μM and 0.30 μM against COX-2 and 5-LOX, respectively) and 3-(4-biphenyl) derivative 30f (IC(50) values of 0.50 μM and 0.15μM against COX-2 and 5-LOX, respectively) were the most potent dual COX-2/5-LOX inhibitors. Intraperitoneal administration of 30c at 100mg/kg demonstrated potent acute anti-inflammatory activity. As a result, benzo[1.3.2]dithiazolium ylide 1,1-dioxide represented a novel scaffold for the exploitation in developing dual COX-2/5-LOX inhibitors.

Nucleosides VIII: 1 Synthesis of 2′, 3′-Dideoxy- and 2′, 3′-Didehydro-2′, 3′-Di Deoxyisoguanosine as Potential Antiretroviral Agents

Abstract 2′, 3′-Didehydro-2′, 3′-dideoxyisoguanosine (2) and 2′, 3′- dideoxyisoguanosine (3) have been synthesized by utilizing the Corey-Winter approach starting from isoguanosine. The 6-amino and 5′-hydroxy biprotected isoguanosine derivative was converted to the corresponding 2′, 3′- thionocarbonate, which was heated with triethyl phosphite to afford the 2′,3′- olefinic product. Either a tert-butyldimethylsilyl or a 4, 4′-dimethoxytrityl group was used in the protection of 5′-hydroxy function. Compounds 2 and 3 were found inactive against human immunodeficiency virus (HIV), human cytomegalovirus (HCMV), and herpes simplex virus type 1 (HSV-1). 1. Previous paper in this series: Chien, T.-C.; Chen, C.-S.; Yeh, J.-Y.; Wang, K.C.; Chern, J.-W. Tetrahedron Lett. 1995, 36, 7881.

Discovery of N-arylalkyl-3-hydroxy-4-oxo-3,4-dihydroquinazolin-2-carboxamide derivatives as HCV NS5B polymerase inhibitors.

The metal ion chelating β‐N‐hydroxy‐γ‐ketocarboxamide pharmacophore was integrated into a quinazolinone scaffold, leading to N‐arylalkyl‐3‐hydroxy‐4‐oxo‐3,4‐dihydroquinazolin‐2‐carboxamide derivatives as hepatitis C virus (HCV) NS5B polymerase inhibitors. Lead optimization led to the identification of N‐phenylpropyl carboxamide 9 k (IC50=8.8 μM). Compound 9 k possesses selectivity toward HCV1b replicon Ava.5 cells (EC50=17.5 μM) over parent Huh‐7 cells (CC50=187.5 μM). Compound 9 k effects a mixed mode of NS5B inhibition, with NTP‐competitive displacement properties. The interaction between 9 k and NS5B is stabilized by the presence of magnesium ions. Docking studies showed that the binding orientation of 9 k occupies the central portions of both magnesium‐mediated and NTP‐ribose‐response binding sites within the active site region of NS5B. As a result, 3‐hydroxy‐4‐oxo‐3,4‐dihydroquinazolin‐2‐carboxamide derivatives are disclosed herein as novel, mainly active site inhibitors of HCV NS5B polymerase.