Neprilysin inhibitors

A compound of formula I:

• where:
• R1 is —OR10 or —NR60R70;
• R2 is H or —OR20;
• R3 is selected from Cl, F, —CH3, and —CF3;
• a is 0 or an integer from 1 to 3;
• R4 is selected from —C1-6alkyl;
• —C3-7cycloalkyl;
• —C0-2alkylene-COOR40;
• —NR41R42;
• —NHC(O)O—C1-6alkyl;
• —NHC(O)R43;
• —NHC(O)NH—R44;
• phenyl substituted with one or two groups independently selected from halo, —O—C1-6alkyl, —C0-1alkylene-COOR40, —SO2NH2, —C(O)NR41R42, and tetrazole;
• and —C0-2alkylene-C1-9heteroaryl or a partially unsaturated —C0-2alkylene-C3-5heterocycle both optionally substituted with 1-3 groups independently selected from halo, —OH, ═O, —CHO, —C1-6alkyl, —CF3, and —COOR40;
• R5 is selected from H, halo, —OH, —C1-6alkyl, —O—C1-6alkyl, phenyl, and morpholine;
• R6 is H or halo;
• R10 and R40 are independently selected from H, —C1-6alkyl, —C1-3alkylene-C6-10aryl, —C1-3alkylene-C1-9heteroaryl, —C3-7cycloalkyl, —[(CH2)2O]1-3CH3, —C1-6alkylene-OC(O)R13, —C1-6alkylene-NR14R15, —C1-6alkylene-C(O)R17, —C0-6alkylenemorpholine, —C1-6alkylene-SO2—C1-6alkyl,
• R13 is selected from —C1-6alkyl, —O—C1-6alkyl, —C3-7cycloalkyl, —O—C3-7cycloalkyl, phenyl, —O-phenyl, —NR14R15, and —CH(NH2)CH2COOCH3;
• R14 and R15 are independently selected from H, —C1-6alkyl, and benzyl, or R14 and R15 are taken together as —(CH2)3-6—, —C(O)—(CH2)3—, or —(CH2)2O(CH2)2—;
• R16 is —C1-6alkyl or —C0-6alkylene-C6-10aryl;
• R17 is selected from —O—C1-6alkyl, —O-benzyl, and —NR14R15;
• R20 is H or is taken together with R10 to form —CR21R22— or is taken together with R60 to form —C(O)—;
• R21 and R22 are independently selected from H, —C1-6alkyl, and —O—C3-7cycloalkyl, or R21 and R22 are taken together to form ═O;
• R43 is selected from —C1-6alkyl, —C1-3alkylene-COOR40, phenyl, and pyridine;
• R44 is selected from —C1-6alkyl, —C1-6alkylene-COOR40, phenyl, and thiophene-COOR40, where thiophene is optionally substituted with CH3;
• R60 is selected from H, —OH, —OC(O)R61, —CH2COOH, —O-benzyl, pyridyl, and —OC(S)NR62R63;
• R61 is selected from H, —C1-6alkyl, —C6-10aryl, —OCH2—C6-10aryl, —CH2O—C6-10aryl, and —NR62R63;
• R70 is selected from H, —C1-6alkyl, and —C(O)R71;
• R71 is selected from H, —C1-6alkyl, —C3-7cycloalkyl, —C6-10aryl, and —C1-9heteroaryl;
• R41, R42, R62, and R63 are independently H or —C1-4alkyl;
• or a pharmaceutically acceptable salt thereof.