A compound of formula: or a pharmaceutically acceptable salt thereof, wherein R is hydrogen, or -CO(C 1 -C 6 alkyl); R 1 is C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, or C 1 -C 6 alkoxy, each optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 6, -NR 6 2, -CO 2 R 6, and -CONR 6 2; where each R 6 independently is hydrogen or C 1 -C 6 alkyl; R 2 is C 7 -C 20 alkyl, C 2 -C 20 alkenyl, or C 2 -C 20 alkynyl, wherein C 7 -C 20 alkyl is optionally substituted with one to four -OR 7, where each R 7 independently is hydrogen, C 1 -C 6 alkyl, or halo(C 1 -C 6 alkyl), and wherein each of C 2 -C 20 alkenyl and C 2 -C 20 alkynyl is optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, and -CON(R 7) 2; where each R 7 independently is hydrogen, C 1 -C 6 alkyl, or halo(C 1 -C 6 alkyl); X is CR 3 or N; where R 3 is hydrogen, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, or -CON(R 7) 2; Y is CR 4 or N; where R 4 is hydrogen, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, -CON(R 7) 2, aryl, heteroaryl or heterocyclyl ring, which is optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, and -CON(R 7) 2; and Z is CR 5 or N; where R 5 is hydrogen, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, or -CON(R 7) 2, or where R 4 and R 5 together with the atoms to which they are attached form 5-7 member heteroaryl or heterocyclyl ring, which is optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, and -CON(R 7) 2, provided that at least one of X, Y, and Z is N. R is hydrogen, or -CO(C 1 -C 6 alkyl); R 1 is C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, or C 1 -C 6 alkoxy, each optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 6, -NR 6 2, -CO 2 R 6, and -CONR 6 2; where each R 6 independently is hydrogen or C 1 -C 6 alkyl; R 2 is C 7 -C 20 alkyl, C 2 -C 20 alkenyl, or C 2 -C 20 alkynyl, wherein C 7 -C 20 alkyl is optionally substituted with one to four -OR 7, where each R 7 independently is hydrogen, C 1 -C 6 alkyl, or halo(C 1 -C 6 alkyl), and wherein each of C 2 -C 20 alkenyl and C 2 -C 20 alkynyl is optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, and -CON(R 7) 2; where each R 7 independently is hydrogen, C 1 -C 6 alkyl, or halo(C 1 -C 6 alkyl); X is CR 3 or N; where R 3 is hydrogen, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, or -CON(R 7) 2; Y is CR 4 or N; where R 4 is hydrogen, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, -CON(R 7) 2, aryl, heteroaryl or heterocyclyl ring, which is optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, and -CON(R 7) 2; and Z is CR 5 or N; where R 5 is hydrogen, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, or -CON(R 7) 2, or where R 4 and R 5 together with the atoms to which they are attached form 5-7 member heteroaryl or heterocyclyl ring, which is optionally substituted with one to four substituents selected from halogen, cyano, nitro, C 1 -C 6 alkyl, halo(C 1 -C 6 alkyl), -OR 7, -NR 7 2, -CO 2 R 7, and -CON(R 7) 2, provided that at least one of X, Y, and Z is N.