Synthesis of Entecavir and Its Novel Class of Analogs

Ravindra K. Rawal1, Uma Sharan Singh1, Srinivas Gadthula1, Chung K. Chu1

1 The University of Georgia College of Pharmacy, Athens, Georgia
Publication Name:  Current Protocols in Nucleic Acid Chemistry
Unit Number:  Unit 14.7
DOI:  10.1002/0471142700.nc1407s47
Online Posting Date:  December, 2011
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Abstract

Due to the slow kinetics of viral clearance and the spontaneous genetic variability of hepatitis B virus (HBV), antiviral therapy of chronic hepatitis B remains a clinical challenge. Entecavir (S.10; a 2′‐deoxy carbocyclic guanosine analog with an exo‐cyclic double bond on the 5′‐position; Fig. 14.7.1) has been approved in the U.S. for the therapy of chronic hepatitis B. Entecavir is synthesized from D‐ribose via a key allylic alcohol (S.3) intermediate. This intermediate is also utilized to synthesize entecavir‐modified carbocyclic nucleosides S.13, S.15, S.19, and S.22. Curr. Protoc. Nucleic Acid Chem. 47:14.7.1‐14.7.17. © 2011 by John Wiley & Sons, Inc.

Keywords: carbocyclic nucleoside; entecavir; Mannich reaction; Hoffman elimination reaction; Mitsunobu coupling

     
 
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Table of Contents

  • Introduction
  • Basic Protocol 1: Preparation of Entecavir from Protected 5‐Exocyclic Methylene Substituted Carbocyclic Moiety
  • Basic Protocol 2: Preparation of 4‐(Hydroxymethyl)‐5‐Methylenecyclopentane‐1,2,3‐Triol Derivatives of Adenine, Guanine, Cytosine, and Thymine
  • Reagents and Solutions
  • Commentary
  • Literature Cited
  • Figures
     
 
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Materials

Basic Protocol 1: Preparation of Entecavir from Protected 5‐Exocyclic Methylene Substituted Carbocyclic Moiety

  Materials
  • n‐Butyl lithium
  • Anhydrous tetrahydrofuran (THF)
  • Argon gas
  • Lithium diisopropylamide (LDA)
  • (3aR,6R,6aR)‐6‐(tert‐butoxymethyl)‐2,2‐dimethyl‐5‐methylenedihydro‐3aH‐cyclopenta‐[d] [1,3]dioxol‐4(5H)‐one ( S.1) (Moon et al., ; Jin et al., )
  • Echenmoser's salt
  • Iodomethane (MeI)
  • Sodium bicarbonate (NaHCO 3)
  • Anhydrous diethyl ether (Et 2O)
  • Brine
  • Anhydrous sodium sulfate (Na 2SO 4)
  • Ethyl acetate (EtOAc)
  • Hexane
  • Cerium (III) chloride heptahydrate (CeCl 3.7H 2O)
  • Anhydrous methanol (MeOH)
  • Sodium borohydride (NaBH 4)
  • Saturated ammonium chloride (NH 4Cl) solution
  • Anhydrous methylene chloride (CH 2Cl 2)
  • Sodium hydride (NaH) in 60% mineral oil
  • Benzyl bromide (BnBr)
  • Trifluoroacetic acid (CF 3COOH)
  • Ethanol (EtOH)
  • Ammonia gas (NH 3)
  • 1,3‐Dichloro‐1,1,3,3‐tetraisopropyldisiloxane (TIPDSCl 2)
  • Imidazole
  • Anhydrous N′N dimethyl formamide (DMF)
  • Anhydrous carbon disulfide (CS 2)
  • Tributyltin hydride (Bu 3SnH)
  • Azobis isobutyronitrile (AIBN)
  • Anhydrous toluene
  • Sodium metal (Na)
  • Diisopropyl azodicarboxlate (DIAD)
  • 2‐Isobutyroylamino‐6‐chloropurine
  • Triphenylphosphine (Ph 3P)
  • Tetrabutylammonium fluoride (TBAF)
  • Formic acid (HCOOH)
  • Methanolic ammonia (see recipe)
  • 1‐L round‐bottom flasks equipped with magnetic stir bar
  • Magnetic stirrer
  • Cannula
  • 3‐L separatory funnel
  • Rotary evaporator
  • Glass funnels with cotton plug
  • Additional reagents and equipment for flash silica gel column chromatography ( appendix 3E)

Basic Protocol 2: Preparation of 4‐(Hydroxymethyl)‐5‐Methylenecyclopentane‐1,2,3‐Triol Derivatives of Adenine, Guanine, Cytosine, and Thymine

  Materials
  • Nitrogen gas (N 2)
  • S.3 (see protocol 1)
  • 6‐Chloropurine
  • Triphenyl phosphine (Ph 3P)
  • Anhydrous tetrahydrofuran (THF)
  • Diisopropyl azodicarboxlate (DIAD)
  • Ethyl acetate (EtOAc)
  • Brine
  • Anhydrous sodium sulfate (Na 2SO 4)
  • Hexane
  • Methanolic ammonia (NH 3/MeOH; see recipe)
  • Trifluoroacetic acid (CF 3CO 2H)
  • Ethanol (EtOH)
  • Anhydrous methylene chloride (CH 2Cl 2)
  • Anhydrous methanol (MeOH)
  • N2i‐Butyroyl‐6‐chloropurine
  • 85% formic acid (HCO 2H)
  • Anhydrous toluene
  • N3‐Benzoyluracil
  • 4‐(Dimethylamino)pyridine (DMAP)
  • Triethylamine (Et 3N)
  • 2,4,6‐Triisopropylbenzenesulfonyl chloride (TIBSCl)
  • Anhydrous acetonitrile (MeCN)
  • 30% ammonium hydroxide (NH 4OH)
  • CHCl 3
  • Saturated ammonium chloride (NH 4Cl) solution
  • N3‐Benzoylthymine
  • Sodium bicarbonate (NaHCO 3)
  • 50‐mL round‐bottom flasks equipped with magnetic stir bars
  • Magnetic stirrer
  • Ice‐salt cooling baths
  • Rotary evaporator
  • 100‐mL separatory funnels
  • 100‐mL capacity steel bomb
  • Preparative TLC (Analtech)
  • Additional reagents and equipment for flash silica gel column chromatography ( appendix 3E)
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Figures

Videos

Literature Cited

Literature Cited
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