A compound having the structure wherein Z is tetrazole or CO 2 Q; each Q is independently selected from hydrogen or a protecting group; and wherein m is 0, 1, 2, 3, 4, 5, or 6; R is a pyridine ring selected from the group consisting of wherein X is fluorine, iodine, a radioisotope of fluorine, a radioisotope of iodine, chlorine, bromine, a radioisotope of bromine, a radioisotope of astatine, NO 2, NH 2, N + (R 2) 3, Sn(R 2) 3, Si(R 2) 3, Hg(R 2), B 2, -NHNH 2, -NHN=CHR 3, -NHNH-CH 2 R 3; n is 1, 2, 3, 4, or 5; Y is O, S, N(R'), C, NR'C, C N(R'), OC, C O, NR'C NR', NR'C NR', NR'S 2, S(CH 2) p, NR'(CH 2) p, O(CH 2) p, OC CHR 8 NHC, NHC CHR 8 NHC, or a covalent bond; wherein p is 1, 2, or 3, R' is H or C 1 -C 6 alkyl, and R 8 is hydrogen, alkyl, aryl or heteroaryl, each of which may be substituted; R 2 is C 1 -C 6 alkyl; and R 3 is alkyl, alkenyl, alkynyl, aryl, or heteroaryl each of which is substituted by fluorine, iodine, a radioisotope of fluorine, a radioisotope of iodine, chlorine, bromine, a radioisotope of bromine, or a radioisotope of astatine, NO 2, NH 2, N + (R 2) 3, Sn(R 2) 3, Si(R 2) 3, Hg(R 2), or B 2; or a pharmaceutically acceptable salt thereof. Z is tetrazole or CO 2 Q; each Q is independently selected from hydrogen or a protecting group; and wherein m is 0, 1, 2, 3, 4, 5, or 6; R is a pyridine ring selected from the group consisting of wherein X is fluorine, iodine, a radioisotope of fluorine, a radioisotope of iodine, chlorine, bromine, a radioisotope of bromine, a radioisotope of astatine, NO 2, NH 2, N + (R 2) 3, Sn(R 2) 3, Si(R 2) 3, Hg(R 2), B 2, -NHNH 2, -NHN=CHR 3, -NHNH-CH 2 R 3; n is 1, 2, 3, 4, or 5; Y is O, S, N(R'), C, NR'C, C N(R'), OC, C O, NR'C NR', NR'C NR', NR'S 2, S(CH 2) p, NR'(CH 2) p, O(CH 2) p, OC CHR 8 NHC, NHC CHR 8 NHC, or a covalent bond; wherein p is 1, 2, or 3, R' is H or C 1 -C 6 alkyl, and R 8 is hydrogen, alkyl, aryl or heteroaryl, each of which may be substituted; R 2 is C 1 -C 6 alkyl; and R 3 is alkyl, alkenyl, alkynyl, aryl, or heteroaryl each of which is substituted by fluorine, iodine, a radioisotope of fluorine, a radioisotope of iodine, chlorine, bromine, a radioisotope of bromine, or a radioisotope of astatine, NO 2, NH 2, N + (R 2) 3, Sn(R 2) 3, Si(R 2) 3, Hg(R 2), or B 2; or a pharmaceutically acceptable salt thereof. wherein X is fluorine, iodine, a radioisotope of fluorine, a radioisotope of iodine, chlorine, bromine, a radioisotope of bromine, a radioisotope of astatine, NO 2, NH 2, N + (R 2) 3, Sn(R 2) 3, Si(R 2) 3, Hg(R 2), B 2, -NHNH 2, -NHN=CHR 3, -NHNH-CH 2 R 3; n is 1, 2, 3, 4, or 5; Y is O, S, N(R'), C, NR'C, C N(R'), OC, C O, NR'C NR', NR'C NR', NR'S 2, S(CH 2) p, NR'(CH 2) p, O(CH 2) p, OC CHR 8 NHC, NHC CHR 8 NHC, or a covalent bond; wherein p is 1, 2, or 3, R' is H or C 1 -C 6 alkyl, and R 8 is hydrogen, alkyl, aryl or heteroaryl, each of which may be substituted; R 2 is C 1 -C 6 alkyl; and R 3 is alkyl, alkenyl, alkynyl, aryl, or heteroaryl each of which is substituted by fluorine, iodine, a radioisotope of fluorine, a radioisotope of iodine, chlorine, bromine, a radioisotope of bromine, or a radioisotope of astatine, NO 2, NH 2, N + (R 2) 3, Sn(R 2) 3, Si(R 2) 3, Hg(R 2), or B 2; or a pharmaceutically acceptable salt thereof.