An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals

Marcus Baumann,
Ian R. Baxendale,
Steven V. Ley and
Nikzad Nikbin

Review
Published 18 Apr 2011

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1. Graphical Abstract
2. Figure 1: Structures of atorvastatin and other commercial statins.
  
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3. Figure 2: Structure of compactin.
  
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4. Scheme 1: Synthesis of pentasubstituted pyrroles.
  
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5. Scheme 2: [3 + 2] Cycloaddition to prepare 5-isopropylpyrroles.
  
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6. Scheme 3: Regiospecific [3 + 2] cycloaddition to prepare the pyrrole scaffold.
  
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7. Scheme 4: Formation of the pyrrole core of atorvastatin via [3 + 2] cycloaddition.
  
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8. Scheme 5: Formation of pyrrole 33 via the Paal–Knorr reaction.
  
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9. Scheme 6: Convergent synthesis towards atorvastatin.
  
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10. Figure 3: Binding pocket of sunitinib in the TRK KIT.
  
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11. Scheme 7: Synthesis of sunitinib.
  
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12. Scheme 8: Alternative synthesis of sunitinib.
  
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13. Scheme 9: Key steps in the syntheses of sumatriptan and zolmitriptan.
  
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14. Scheme 10: Introduction of the N,N-dimethylaminoethyl side chain.
  
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15. Scheme 11: Japp–Klingemann reaction in the synthesis of sumatriptan.
  
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16. Scheme 12: Synthesis of the intermediate sulfonyl chlorides 62 and 63.
  
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17. Scheme 13: Alternative introduction of the sulfonamide.
  
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18. Scheme 14: Negishi-type coupling to benzylic sulfonamides.
  
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19. Scheme 15: Heck reaction used to introduce the sulfonamide side chain of naratriptan.
  
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20. Scheme 16: Synthesis of the oxazolinone appendage of zolmitriptan.
  
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21. Scheme 17: Grandberg indole synthesis used in the preparation of rizatriptan.
  
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22. Scheme 18: Improved synthesis of rizatriptan.
  
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23. Scheme 19: Larock-type synthesis of rizatriptan.
  
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24. Scheme 20: Synthesis of eletriptan.
  
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25. Scheme 21: Heck coupling for the indole system in eletriptan.
  
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26. Scheme 22: Attempted Fischer indole synthesis of elatriptan.
  
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27. Scheme 23: Successful Fischer indole synthesis for eletriptan.
  
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28. Scheme 24: Mechanistic rationale for the Bischler–Möhlau reaction.
  
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29. Scheme 25: Bischler-type indole synthesis used in the fluvastatin sodium synthesis.
  
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30. Scheme 26: Palladium-mediated synthesis of ondansetron.
  
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31. Scheme 27: Fischer indole synthesis of ondansetron.
  
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32. Scheme 28: Optimised Pictet–Spengler reaction towards tadalafil.
  
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33. Figure 4: Structures of carvedilol 136 and propranolol 137.
  
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34. Scheme 29: Synthesis of the carbazole core of carvedilol.
  
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35. Scheme 30: Alternative syntheses of 4-hydroxy-9H-carbazole.
  
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36. Scheme 31: Convergent synthesis of etodolac.
  
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37. Scheme 32: Alternative synthesis of etodolac.
  
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38. Figure 5: Structures of imidazole-containing drugs.
  
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39. Scheme 33: Synthesis of functionalised imidazoles towards losartan.
  
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40. Scheme 34: Direct synthesis of the chlorinated imidazole in losartan.
  
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41. Scheme 35: Synthesis of trisubstituted imidazoles.
  
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42. Scheme 36: Preparation of the imidazole ring in olmesartan.
  
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43. Scheme 37: Synthesis of ondansetron.
  
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44. Scheme 38: Alternative route to ondansetron and its analogues.
  
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45. Scheme 39: Proton pump inhibitors and synthesis of esomeprazole.
  
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46. Scheme 40: Synthesis of benzimidazole core pantoprazole.
  
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47. Figure 6: Structure of rabeprazole 194.
  
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48. Scheme 41: Synthesis of candesartan.
  
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49. Scheme 42: Alternative access to the candesartan key intermediate 216.
  
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50. Scheme 43: .Medicinal chemistry route to telmisartan.
  
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51. Scheme 44: Improved synthesis of telmisartan.
  
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52. Scheme 45: Synthesis of zolpidem.
  
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53. Scheme 46: Copper-catalysed 3-component coupling towards zolpidem.
  
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54. Figure 7: Structure of celecoxib.
  
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55. Scheme 47: Preparation of celecoxib.
  
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56. Scheme 48: Alternative synthesis of celecoxib.
  
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57. Scheme 49: Regioselective access to celecoxib.
  
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58. Scheme 50: Synthesis of pazopanib.
  
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59. Scheme 51: Syntheses of anastrozole, rizatriptan and letrozole.
  
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60. Scheme 52: Regioselective synthesis of anastrozole.
  
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61. Scheme 53: Triazine-mediated triazole formation towards anastrozole.
  
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62. Scheme 54: Alternative routes to 1,2,4-triazoles.
  
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63. Scheme 55: Initial synthetic route to sitagliptin.
  
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64. Figure 8: Binding of sitagliptin within DPP-IV.
  
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65. Scheme 56: The process route to sitagliptin key intermediate 280.
  
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66. Scheme 57: Synthesis of maraviroc.
  
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67. Scheme 58: Synthesis of alprazolam.
  
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68. Scheme 59: The use of N-nitrosoamidine derivatives in the preparation of fused benzodiazepines.
  
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69. Figure 9: Structures of itraconazole, ravuconazole and voriconazole.
  
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70. Scheme 60: Synthesis of itraconazole.
  
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71. Scheme 61: Synthesis of rufinamide.
  
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72. Scheme 62: Representative tetrazole formation in valsartan.
  
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73. Figure 10: Structure of tetrazole containing olmesartan, candesartan and irbesartan.
  
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74. Scheme 63: Early stage introduction of the tetrazole in losartan.
  
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75. Scheme 64: Synthesis of cilostazol.
  
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76. Figure 11: Structure of cefdinir.
  
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77. Scheme 65: Semi-synthesis of cefdinir.
  
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78. Scheme 66: Thiazole syntheses towards ritonavir.
  
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79. Scheme 67: Synthesis towards pramipexole.
  
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80. Scheme 68: Alternative route to pramipexole.
  
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81. Scheme 69: Synthesis of famotidine.
  
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82. Scheme 70: Efficient synthesis of the hyperuricemic febuxostat.
  
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83. Scheme 71: Synthesis of ziprasidone.
  
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84. Figure 12: Structure of mometasone.
  
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85. Scheme 72: Industrial access to 2-furoic acid present in mometasone.
  
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86. Scheme 73: Synthesis of ranitidine from furfuryl alcohol.
  
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87. Scheme 74: Synthesis of nitrofurantoin.
  
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88. Scheme 75: Synthesis of benzofuran.
  
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89. Scheme 76: Synthesis of amiodarone.
  
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90. Scheme 77: Synthesis of raloxifene.
  
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91. Scheme 78: Alternative access to the benzo[b]thiophene core of raloxifene.
  
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92. Scheme 79: Gewald reaction in the synthesis of olanzapine.
  
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93. Scheme 80: Alternative synthesis of olanzapine.
  
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94. Figure 13: Access to simple thiophene-containing drugs.
  
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95. Scheme 81: Synthesis of clopidogrel.
  
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96. Scheme 82: Pictet–Spengler reaction in the preparation of tetrahydrothieno[3,2-c]pyridine (422).
  
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97. Scheme 83: Alternative synthesis of key intermediate 422.
  
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98. Figure 14: Co-crystal structures of timolol (left) and carazolol (right) in the β-adrenergic receptor.
  
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99. Scheme 84: Synthesis of timolol.
  
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100. Scheme 85: Synthesis of tizanidine 440.
  
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101. Scheme 86: Synthesis of leflunomide.
  
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102. Scheme 87: Synthesis of sulfamethoxazole.
  
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103. Scheme 88: Synthesis of risperidone.
  
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104. Figure 15: Relative abundance of selected transformations.
  
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105. Figure 16: The abundance of heterocycles within top 200 drugs (5-membered rings).
  
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