A compound of Formula: or a pharmaceutically acceptable salt thereof, wherein R 1a is selected from the group consisting of-H, -OH, and -F; R 1b is selected from the group consisting of-H, -OH, and -F, wherein at least one of R 1a and R 1b is -H; R 4a is selected from the group consisting of-H, -OH, and -F; R 4b is selected from the group consisting of-H, -OH, and -F, wherein at least one of R 4a and R 4b is -H; P 1 and P 2 each independently has an S or R stereochemical configuration; Z is -O- or -NH-; X 1a and X 2a are the same or different and are independently selected from =O or =S; X 1b and X 2b are the same or different and are independently selected from -OR 5 and -SR 5; wherein R 5 is selected from the group consisting of-H, -C 1-6 alkyl, -C C 1-6 alkyl, and -CH 2 OC OC 1-6 alkyl; L 1 in formula is four, five, or six carbons in length, and is wherein indicates a single bond, a double bond, or a triple bond and wherein (i) either 0 or 1 occurrence of in L 1 indicates a triple bond; or (ii) 0, 1, or 2 occurrences of in L 1 indicates a double bond, wherein geometry about each double bond is cis or trans; and (iii) wherein when 1 occurrence of in L 1 indicates a triple bond, 0 occurrences of in L 1 indicates a double bond; and (iv) wherein, when 2 occurrences of in L 1 indicate a double bond, those double bonds are either adjacent bonds or alternating bonds; wherein X 10, X 11, X 12, X 13, X 14, and X 15 are independently selected from a bond, - CH 2 -, or -CH-, wherein the -CH 2 - or -CH- is unsubstituted or substituted by (i) -OH, (ii) - F, (iii) -Cl, (iv) -NH 2, or (v) -D, and when X 10 or X 15 is a bond, that bond is not a double bond or triple bond; and wherein any two adjacent members of the group including X 10, X 11, X 12, X 13, X 14, and X 15 may optionally form, with additional atoms, a C 3 cycloalkyl or a C 3 heterocycloalkyl, said C 3 heterocycloalkyl including an N or O atom; wherein B 1 and B 2 are independently selected from: where the bonds at points q and r on B 1 and B 2 are attached at points q and r on Formula. R 1a is selected from the group consisting of-H, -OH, and -F; R 1b is selected from the group consisting of-H, -OH, and -F, wherein at least one of R 1a and R 1b is -H; R 4a is selected from the group consisting of-H, -OH, and -F; R 4b is selected from the group consisting of-H, -OH, and -F, wherein at least one of R 4a and R 4b is -H; P 1 and P 2 each independently has an S or R stereochemical configuration; Z is -O- or -NH-; X 1a and X 2a are the same or different and are independently selected from =O or =S; X 1b and X 2b are the same or different and are independently selected from -OR 5 and -SR 5; wherein R 5 is selected from the group consisting of-H, -C 1-6 alkyl, -C C 1-6 alkyl, and -CH 2 OC OC 1-6 alkyl; L 1 in formula is four, five, or six carbons in length, and is wherein indicates a single bond, a double bond, or a triple bond and wherein (i) either 0 or 1 occurrence of in L 1 indicates a triple bond; or (ii) 0, 1, or 2 occurrences of in L 1 indicates a double bond, wherein geometry about each double bond is cis or trans; and (iii) wherein when 1 occurrence of in L 1 indicates a triple bond, 0 occurrences of in L 1 indicates a double bond; and (iv) wherein, when 2 occurrences of in L 1 indicate a double bond, those double bonds are either adjacent bonds or alternating bonds; wherein X 10, X 11, X 12, X 13, X 14, and X 15 are independently selected from a bond, - CH 2 -, or -CH-, wherein the -CH 2 - or -CH- is unsubstituted or substituted by (i) -OH, (ii) - F, (iii) -Cl, (iv) -NH 2, or (v) -D, and when X 10 or X 15 is a bond, that bond is not a double bond or triple bond; and wherein any two adjacent members of the group including X 10, X 11, X 12, X 13, X 14, and X 15 may optionally form, with additional atoms, a C 3 cycloalkyl or a C 3 heterocycloalkyl, said C 3 heterocycloalkyl including an N or O atom; wherein B 1 and B 2 are independently selected from: where the bonds at points q and r on B 1 and B 2 are attached at points q and r on Formula. wherein X 10, X 11, X 12, X 13, X 14, and X 15 are independently selected from a bond, - CH 2 -, or -CH-, wherein the -CH 2 - or -CH- is unsubstituted or substituted by (i) -OH, (ii) - F, (iii) -Cl, (iv) -NH 2, or (v) -D, and when X 10 or X 15 is a bond, that bond is not a double bond or triple bond; and wherein any two adjacent members of the group including X 10, X 11, X 12, X 13, X 14, and X 15 may optionally form, with additional atoms, a C 3 cycloalkyl or a C 3 heterocycloalkyl, said C 3 heterocycloalkyl including an N or O atom; wherein B 1 and B 2 are independently selected from: where the bonds at points q and r on B 1 and B 2 are attached at points q and r on Formula.