A compound of the formula: wherein: R 1 and R 2 are each independently selected from hydrogen, hydroxy, alkyl (C1-12), substituted aikyl (C1-12), alkenyl (C2-12), substituted alkenyl (C2 - 12), alkynyl (C2-12), substituted alkynyl (C2-12), aryl (C6-12), substituted aryl (C6-12), aralkyl (C7-12), substituted aralkyl (C7-12), heteroaryl (C1-12), substituted heteroaryl (C1-12), heterocycloalkyl (C2-12), substituted heterocycloalkyl (C2-12), acyl (C1-12), substituted acyl (C1-12), acyloxy (C1-12), substituted acyloxy (C1-12), alkylamino (C1-12), substituted alkylamino (C1-12); a monovalent amine protecting group, -C O(CH 2) n S-A 1, -C O(CH 2) n S -A 1, or -C O(CH 2) n S 2 -A 1, wherein: A 1 is aryl (C6-12) or substituted aryl (C6-12); and n is 1, 2, 3, 4, or 5; or R 1 and R 2 are taken together and form a divalent amine protecting group, R 3 is hydrogen, hydroxy, halo, or alkoxy (C1-12) or substituted alkoxy (C1-12); o is 1, 2, or 3; R 4 is hydrogen, a monovalent amine protecting group, alkyl (C1-12), or substituted alkyl (C1-12); R 5, R 6, and R 7 are each independently hydrogen, hydroxy, amino, mercapto, -OX 1, -NX 2 X 3, or -SX 4; or alkyl (C1-12) or substituted alkyl (C1-12); wherein: X 1 is a hydroxy protecting group; X 2 and X 3 are independently selected from hydrogen, a monovalent amine protecting group, or when X 2 and X 3 are taken together form a divalent amine protecting group; and X 4 is a thiol protecting group; and R 8 is hydroxy, amino, or mercapto; wherein: each amine protecting group is independently selected from the list consisting of formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoroacetyl, trichloroacetyl, o-nitrophenoxyacetyl, α-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, a sulfonyl group, an aralkyl group, and a silyl group; the hydroxyl protecting group is selected from the list consisting of as formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoroacetyl, trichloroacetyl, o-nitrophenoxyacetyl, α-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, a sulfonyl group, an acyloxy group, an aralkyl group, and a silyl group; and the thiol protecting group is selected from the list consisting of formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoroacetyl, trichloroacetyl, o-nitrophenoxyacetyl, α-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, a sulfonyl group, an acyloxy group, an aralkyl group, and a silyl group; or a pharmaceutically acceptable salt thereof. R 1 and R 2 are each independently selected from hydrogen, hydroxy, alkyl (C1-12), substituted aikyl (C1-12), alkenyl (C2-12), substituted alkenyl (C2 - 12), alkynyl (C2-12), substituted alkynyl (C2-12), aryl (C6-12), substituted aryl (C6-12), aralkyl (C7-12), substituted aralkyl (C7-12), heteroaryl (C1-12), substituted heteroaryl (C1-12), heterocycloalkyl (C2-12), substituted heterocycloalkyl (C2-12), acyl (C1-12), substituted acyl (C1-12), acyloxy (C1-12), substituted acyloxy (C1-12), alkylamino (C1-12), substituted alkylamino (C1-12); a monovalent amine protecting group, -C O(CH 2) n S-A 1, -C O(CH 2) n S -A 1, or -C O(CH 2) n S 2 -A 1, wherein: A 1 is aryl (C6-12) or substituted aryl (C6-12); and n is 1, 2, 3, 4, or 5; or R 1 and R 2 are taken together and form a divalent amine protecting group, A 1 is aryl (C6-12) or substituted aryl (C6-12); and n is 1, 2, 3, 4, or 5; or R 1 and R 2 are taken together and form a divalent amine protecting group, R 3 is hydrogen, hydroxy, halo, or alkoxy (C1-12) or substituted alkoxy (C1-12); o is 1, 2, or 3; R 4 is hydrogen, a monovalent amine protecting group, alkyl (C1-12), or substituted alkyl (C1-12); R 5, R 6, and R 7 are each independently hydrogen, hydroxy, amino, mercapto, -OX 1, -NX 2 X 3, or -SX 4; or alkyl (C1-12) or substituted alkyl (C1-12); wherein: X 1 is a hydroxy protecting group; X 2 and X 3 are independently selected from hydrogen, a monovalent amine protecting group, or when X 2 and X 3 are taken together form a divalent amine protecting group; and X 4 is a thiol protecting group; and X 1 is a hydroxy protecting group; X 2 and X 3 are independently selected from hydrogen, a monovalent amine protecting group, or when X 2 and X 3 are taken together form a divalent amine protecting group; and X 4 is a thiol protecting group; and R 8 is hydroxy, amino, or mercapto; wherein: each amine protecting group is independently selected from the list consisting of formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoroacetyl, trichloroacetyl, o-nitrophenoxyacetyl, α-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, a sulfonyl group, an aralkyl group, and a silyl group; the hydroxyl protecting group is selected from the list consisting of as formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoroacetyl, trichloroacetyl, o-nitrophenoxyacetyl, α-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, a sulfonyl group, an acyloxy group, an aralkyl group, and a silyl group; and the thiol protecting group is selected from the list consisting of formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoroacetyl, trichloroacetyl, o-nitrophenoxyacetyl, α-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, a sulfonyl group, an acyloxy group, an aralkyl group, and a silyl group; or