Analgesic compounds, methods, and formulations

A compound, or salt thereof, of formula I:

• wherein A is
• R1 is hydrogen, C1-C5 alkyl, C1-C5 haloalkyl, C1-C5 alkanol, —(C1-C5 alkyl)phenyl, or phenyl, or a group of the formula —C(O)—R12, where R12 is C1-C5 alkyl, C1-C5 alkoxy, C1-C5 haloalkyl, C1-C5 alkanol, —(C1-C5 alkyl)phenyl, or phenyl;
• R2 is hydrogen, C1-C5 alkyl, C1-C5 alkoxy, halogen, C1-C5 haloalkyl, or C1-C5 haloalkoxy;
• R3 is hydrogen, C1-C5 alkyl, C1-C5 alkoxy, halogen, C1-C5 haloalkyl, or C1-C5 haloalkoxy;
• R4 is hydrogen, C1-C5 alkyl, or —(C1-C5 alkyl)phenyl;
• R5 is hydrogen, C1-C5 alkyl, or —(C1-C5 alkyl)phenyl;
• R6 is hydrogen, hydroxy, or is absent;
• R7 is hydrogen;
• R8 is hydrogen or methyl;
• R9 is hydrogen or methyl;
• R10 is hydrogen;
• R11 is hydrogen or C1-C5 alkyl;
• provided that one of A), B), and C) is present, wherein A), B) and C) are:
• A) R7 and R10 combine to form —CH2— or —(CH2)2—;
• B) R8 and R9 combine to form a cyclopropyl group with the carbon to which they are attached;
• and
• C) R10 and R11 combine to form —CH2— or —(CH2)3.