A compound of structural Formula I: or pharmaceutically acceptable salt thereof, wherein: R A is a D-amino acid ester residue of formula (i) or a D-proline ester residue of formula (ii): R 1, if present, is (a) H, or (b) -C 1-3 alkyl; R 2, if present, is (a) H, (b) -C 1-4 alkyl; R 3 is (a) -C 1-10 alkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 7, -SH, -NR 8 R 9, -C 3-6 cycloalkyl or spiro-C 3-6 cycloalkyl; or (b) -C 3-8 cycloalkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 10, -SH, -NR 8 R 9 or -C 1-3 alkyl; R B is a geminally di-substituted amino acid ester residue of formula (iii): R 4 and R 5 are each independently selected from -CH 3, -CH 2 CH 3, -C 3 alkyl or -C 4 alkyl; or R 4 and R 5 are joined together with the carbon to which they are both attached to form -C 3-6 cycloalkyl or a 4 to 6-membered heterocyclic ring; R 6 is (a) -C 1-10 alkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 11, -SH, -NR 12 R 13, -C 3-6 cycloalkyl or spiro-C 3-6 cycloalkyl; or (b) -C 3-8 cycloalkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 14, -SH, -NR 12 R 13 or -C 1-3 alkyl; R 7 and R 11 are each independently selected from -H or -C 3-6 cycloalkyl; R 8 and R 9 are each independently selected from -H, -C 1-3 alkyl or -C 3-6 cycloalkyl; R 12 and R 13 are each independently selected from -H, -C 1-3 alkyl or -C 3-6 cycloalkyl; and R 10 and R 14 are each independently selected from -H, -C 1-3 alkyl or -C 3-6 cycloalkyl. R A is a D-amino acid ester residue of formula (i) or a D-proline ester residue of formula (ii): R 1, if present, is (a) H, or (b) -C 1-3 alkyl; R 2, if present, is (a) H, (b) -C 1-4 alkyl; R 3 is (a) -C 1-10 alkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 7, -SH, -NR 8 R 9, -C 3-6 cycloalkyl or spiro-C 3-6 cycloalkyl; or (b) -C 3-8 cycloalkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 10, -SH, -NR 8 R 9 or -C 1-3 alkyl; (a) -C 1-10 alkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 7, -SH, -NR 8 R 9, -C 3-6 cycloalkyl or spiro-C 3-6 cycloalkyl; or (b) -C 3-8 cycloalkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 10, -SH, -NR 8 R 9 or -C 1-3 alkyl; R B is a geminally di-substituted amino acid ester residue of formula (iii): R 4 and R 5 are each independently selected from -CH 3, -CH 2 CH 3, -C 3 alkyl or -C 4 alkyl; or R 4 and R 5 are joined together with the carbon to which they are both attached to form -C 3-6 cycloalkyl or a 4 to 6-membered heterocyclic ring; R 6 is (a) -C 1-10 alkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 11, -SH, -NR 12 R 13, -C 3-6 cycloalkyl or spiro-C 3-6 cycloalkyl; or (b) -C 3-8 cycloalkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 14, -SH, -NR 12 R 13 or -C 1-3 alkyl; (a) -C 1-10 alkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 11, -SH, -NR 12 R 13, -C 3-6 cycloalkyl or spiro-C 3-6 cycloalkyl; or (b) -C 3-8 cycloalkyl unsubstituted or substituted with one to three substituents independently selected from fluoro, chloro, bromo, -OR 14, -SH, -NR 12 R 13 or -C 1-3 alkyl; R 7 and R 11 are each independently selected from -H or -C 3-6 cycloalkyl; R 8 and R 9 are each independently selected from -H, -C 1-3 alkyl or -C 3-6 cycloalkyl; R 12 and R 13 are each independently selected from -H, -C 1-3 alkyl or -C 3-6 cycloalkyl; and R 10 and R 14 are each independently selected from -H, -C 1-3 alkyl or -C 3-6 cycloalkyl.