Tai-Shun Lin

Anti-HIV-1 activity and cellular pharmacology of various analogs of gossypol

We previously reported that the racemic mixture and both enantiomers of gossypol inhibit the replication of human immunodeficiency virus-type 1 (HIV-1) (Lin et al., Antimicrob Agents Chemother 33: 2149-2151, 1989). The present study evaluates the activities of a variety of analogs of gossypol as well as a few non-gossypol analogs. Compounds 2, 3, 10, and 13 were slightly more inhibitory than (-)-gossypol to the replication of HIV-1 in cell culture. Compounds 4 and 8 were cytotoxic to human peripheral blood monocyte (PBM) cells, and compounds 2 and 3 were cytotoxic to Vero cells but not PBM cells. The effects of the two enantiomers of gossypol on the cell volume and migration of H9 cells through the cell cycle were evaluated during 72 hr of incubation. The (-)-enantiomer of gossypol was more toxic to H9 cells than the (+)-enantiomer of gossypol as evidenced by cell destruction. Prior to cell destruction, there appeared to be no significant effect on cell cycle distribution with either enantiomer.

Synthesis of several pyrimidine l-nucleoside analogues as potential antiviral agents

Abstract β- l -5-Iodo-2′-deoxyuridine (β- l -IUdR, 7) and 1-[(β- l - arabinofuranosyl )-E-5-(2- bromovinyl)]uracil (β- l -BV-ara-U, 10) have been synthesized via a multi-step synthesis from l -arabinose. 2′,3′-Dideoxy-β- l -5-azacytidine (18), 2′,3′-dideoxy-β- l -2-thiocytidine (20) and their respective α-anomers, compounds 19 and 21, also were synthesized by direct coupling of 1-O- acetyl -5-O-(tert- butyldimethylsilyl )-2,3-dideoxy- l - ribofuranose (13) with the corresponding silylated bases, in the presence of EtAlCl2 in CH2Cl2, followed by separation of the α- and β-isomers and deblocking of the 5′-protecting groups. In addition, 2′,3′-dideoxy-β- l -5-fluorocytidine (34), a potent anti-HIV and anti-HBV agent, was synthesized by an alternative methodology from 2′,3′-dideoxy-β- l -5-fluorouridine (31) via a 4-triazolylpyrimidinone intermediate. These l -nucleoside analogues were tested in vitro against HIV, HBV, HSV-1, and HSV-2. Among these compounds, 2′,3′-dideoxy-β- l -5-azacytidine (18) was found to show significant activity against HBV in vitro at approximately the same level as 2′,3′-dideoxy-β- d -cytidine (ddC), which is a known potent anti-HBV agent.

5-Fluoro-2-pyrimidinone, a liver aldehyde oxidase-activated prodrug of 5-fluorouracil

5-Fluorouracil (5-FU) is an effective antitumor agent used in treating various cancers. Because of its metabolism by intestinal and other cells, 5-FU has an inconsistent bioavailability that limits its oral use. 5-Fluoro-2-pyrimidione (5-FP), a 5-FU prodrug, was synthesized and found to be converted to 5-FU by aldehyde oxidase, an enzyme present in high concentrations in the livers of mice and humans but not in the gastrointestinal tract. Using BDF1 mice, the pharmacokinetics of 5-FP were studied and compared with those of 5-FU. The bioavailability of 5-FP given orally was 100% at a dosage of 25 mg/kg and 78% at a dosage of 50 mg/kg. The half-lives of both doses of 5-FP were at least 2-fold longer than the half-lives of the same doses of 5-FU, and the clearance rates of 5-FP were 3-fold slower. 5-FP was converted rapidly to 5-FU, in vivo. The resulting 5-FU was measured at a steady-state level of 40-70 microM in plasma, at a dosage of 25 mg/kg, that was sustained for at least 4 hr. Also, when given orally, 5-FP was shown to have potent activity against Colon 38 tumor cells and P388 leukemia cells in mice. The therapeutic index of 5-FP was similar to that of 5-FU in these mouse tumor models. The potential clinical use of 5-FP as a prodrug of 5-FU should be considered.

Synthesis and biological evaluation of l- and d-configuration 1,3-dioxolane 5-azacytosine and 6-azathymine nucleosides

Novel L- and D-configuration dioxolane 5-azacytosine and 6-azathymine nucleosides have been synthesized and evaluated for biological activity. (-)-(2S,4S)-1-[2-(Hydroxymethyl)-1,3-dioxolan-4-yl]-5-azacytosine (6) showed significant activity against HBV, whereas the D-configuration analogue (14) has been found to exhibit potent anti-HIV activity.

Potential targets for antiviral chemotherapy

Serendipity and random screening have been successful in producing effective antiviral agents. The increase in our knowledge of the basic biochemistry of viral replication and of virus-host interrelationships has revealed not only an understanding of the targets upon which existing antiviral agents exert their inhibitory effect, but also has uncovered new potential targets. The hope is that such molecular understanding will afford the synthesis of compounds with selective antiviral activity. A review of various viral targets which are potentially susceptible to attack, and a few approaches for development of antiviral agents are presented.

SYNTHESIS OF HALOGEN-SUBSTITUTED 3-DEAZAADENOSINE AND 3-DEAZAGUANOSINE ANALOGUES AS POTENTIAL ANTITUMOR/ANTIVIRAL AGENTS

Various 2-halogen-substituted analogues (38, 39, 43 and 44), 3-halogen- substituted analogues (51 and 52), and 2′, 3′-dihalogen-substituted analogues (57–60) of 3-deazaadenosine and 3-halogen-substituted analogues (61 and 62) of 3-deazaguanosine have been synthesized as potential anticancer and/or antiviral agents. Among these compounds, 3-deaza-3-bromoguanosine (62) showed significant cytotoxicity against L1210, P388, CCRF-CEM and B16F10 cell lines in vitro, producing IC50 values of 3, 7, 9 and 7,μM, respectively. Several 3-deazaadenosine analogues (38, 51, 57 and 59) showed moderate to weak activity against hepatitis B virus. †Deceased.

A stereospecific synthesis of 2′,3′-dideoxy-β-l-cytidine (β-l-ddC), a potent inhibitor against human hepatitis B virus (HBV) and human immunodeficiency virus (HIV)

Abstract 2′,3′-Dideoxy-β- l -cytidine (β- l -ddC), a potent inhibitor against human hepatitis B virus (HBV) and human immunodeficiency virus (HIV), has been stereospecifically synthesized from l -arabinose in 9 steps.

SYNTHESIS OF A SERIES OF PURINE 2',3'-DIDEOXY-L-NUCLEOSIDE ANALOGUES AS POTENTIAL ANTIVIRAL AGENTS

Abstract Various 2′,3′-dideoxy-L-nucleoside analogues, 6-amino-9-(2,3-dideoxy-β-L-ribofuranosyl) purine (19), 2-chloro-6-amino-9-(2,3-dideoxy-β-L-ribofuranosyl)-purine (20), 2-chloro-6-amino-9-(2,3-dideoxy-4-thio-β-L-ribofuranosyl) purine (21), 2,6-diamino-9-(2,3-dideoxy-β-L-ribofuranosyl) purine (26), 2,6-diamino-9-(2,3-dideoxy-β-thio-β-L-ribofuranosyl)-purine (27), 2-amino-6-chloro-9-(2,3-dideoxy-β-L-ribofuranosyl) purine (28), 6-chloro-9-(2,3-dideoxy-4-thio-β-L-ribofuranosyl) purine (29), and 6-amino-9-(2,3-dideoxy-4-thio-β-L-ribofuran-osyl) purine (30) have been synthesized by coupling of the sodium salt of 2-amino-6-chloropurine (1), 6-chloropurine (2), and 2,6-dichloropurine (3) with 1-O-acetyl-5-O-(tert-butyldimethylsilyl)-2,3-dideoxy-L-ribofuranose (4) or 1-O-acetyl-5-O-(tert-butyldimethylsilyl)-2,3-dideoxy-4-thio-L-ribofuranose (5) in anhydrous MeCN in the presence of either EtAlCl2 or Et2AlCl followed by separation of the α/β-anomers and deprotection of the blocking groups. However, the synthesi...

Synthesis of 2',3'-unsaturated and 2',3'-dideoxy analogs of 6-azapyrimidine nucleosides as potential anti-HIV agents

Abstract Several 2′, 3′-unsaturated and 2′, 3′-dideoxy analogs of 6-azapyrimidine nucleosides, compounds 2′, 3′ -dideoxy-6-azacytidine (12), 2′, 3′ -dideoxy-6-azauridin-2′ - ene (15a), 3′ -deoxy-6-azathymidin-2′ -ene (15b) and 3′ -deoxy-6-azathymidine (16b), have been synthesized via a multi-step synthesis from 6-azauridine and 6-azathymidine, respectively. These compounds were evaluated against HIV-1 in vitro and found to be inactive.

Structural Features of 2′,3′-Dideoxy-2′,3′-Didehydrocytidine, A Potent Inhibitor of the HIV (AIDS) Virus

Abstract The structure and conformation of 2′,3′-dideoxy-2′,3′-didehydrocytidine (2′,3′-dideoxycytidin-2′-ene, d4C), a potent inhibitor of the human immunodeficiency virus, was determined by X-ray crystallography. The nucleoside crystallizes in the orthorhombic space group P212121 with cell dimensions a = 8.603(1), b = 9.038(1), c = 25.831(2) A and with two independent molecules in the asymmetric unit (Z = 8). Atomic parameters were refined by full-matrix least squares to a final value of R = 0.033 for 2258 observed reflections. The molecules are quite flexible: in molecule A the glycosyl torsion angle (XCN) is 61.3° and the -CH2OH side chain is in the gauche + orientation while in molecule B XCN = 19.8° and the side chain is trans. The five-membered rings are slightly puckered (∼0.1 A), 04′ being endo in molecule A and exo in molecule B. A mechanism is proposed for the known instability of 2′,3′-unsaturated nucleosides.