Potent 7-Hydroxy-l,2,3,4-tetrahydroisoquinoline-3-carboxylic Acid-Based Macrocyclic Inhibitors of Hepatitis C Virus NS3 Protease

摘要

The NS3 protease of hepatitis C virus (HCV) has emerged as one of the best characterized targets for next-generation HCV therapy.The tetrapeptide 1 and pentapeptide 2 are alpha-ketoamide-type HCV serine protease inhibitors with modest potency.We envisioned that the l,2,3,4-tetrahydroisoquinoline-3-carboxylamide (Tic) moiety could be cyclized to the P3 capping group.The resulting macrocycle could enhance the binding through its extra contact with the Ala156 methyl group.Macrocyclization could also provide a less peptidic HCV inhibitor.Synthesis started from dipeptide 5,which was obtained via a coupling of two amino acid derivatives.The N-terminal was capped as hept-6-enoylamide to give 6.Hydroboration of the double bond afforded alcohol 7,the precursor to the macrocycle 8.The macrocyclization was achieved under Mitsunobu conditions (PPh_3,ADDP).The macrocyclic acid 9 was then combined with appropriate right-hand fragments 12,14,or 16,which was prepared from common intermediate 11.Finally,oxidation of alpha-hydroxyamide provided target molecule alpha-ketoamides 17,18,and 21.The C-terminal esters were then elaborated to carboxylic acids 19 and 20,and amides 20 and 23.The inhibitors 17-23 were tested in HCV NS3 protease continuous assay.Tripeptide 17 was more potent than the larger acyclic tetrapeptide 1.The tetrapeptides 18-20 were as active as 17.Most significantly,the pentapeptides (21-23) were much better inhibitors (K_i = 0.015-0.26 mu M).The carboxylic acid (22) and amide (23) were 57-80 times more potent than the acyclic analogue 2.The X-ray crystal structure of compound 23 bound to the protease revealed that the macrocycle adopted a donutlike conformation and had close contact with the Ala 156 methyl group.The ketone carbonyl formed a reversible covalent bond with Ser139.The n-propyl of P1 novaline and the aromatic ring of P2' phenylglycine formed a C-shaped clamp around the Lys136 side chain.