N-hydroxy 4-sulfonyl butanamide compounds

A compound or a salt thereof, wherein:

• the compound corresponds in structure to Formula I:
• R1 is cyclohydrocarbyl, heterocyclo, aryl, or heteroaryl. wherein such substituent:
• has 5 or 6 ring members, and
• is substituted at its own 4-position when a 6-membered ring and at its own 3- or 4-position when a 5-membered ring with a substituent, R4;
• R4 is selected from the group consisting of single-ringed cyclohydrocarbyl, single-ringed heterocyclo, single-ringed aryl, single-ringed heteroaryl, C3-C14 hydrocarbyl, C2-C14 hydrocarbyloxy, phenoxy, thiophenoxy group, 4-thiopyridyl, phenylazo, phenylureido, nicotinamido, isonicotinamido, picolinamido, anilino, and benzamido;
• as to R2 and R3:
• R3 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R2 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R2 and R3, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring, wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent selected from the group consisting of C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• as to R6 and R7:
• R7 is independently selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R6 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R6 and R7, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent selected from the group consisting of C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• each —Y is independently selected from the group consisting of —O and —NR11;
• each R11 is independently selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• each —Z is independently selected from the group consisting of hydrido, C1-C4 hydrocarbyl, benzoyl, (2-pyridinyl)methyl, (3-pyridinyl)methyl, (4-pyridinyl)methyl, 2-(morpholinyl)ethyl, 2-(piperidinyl)ethyl, 2-(piperazinyl)ethyl, 2-(N-methylpiperazinyl)ethyl, 2-(thiomorpholinyl)ethyl, 2-(thiomorpholinyl sulfone)ethyl, 2-(succinimidyl)ethyl, 2-(hydantoinyl), 2-(3-methylhydantoinyl)ethyl, 2-(N-C1-C4 hydrocarbylamino)ethyl, 2-[N,N-di(C1-C4 hydrocarbyl)amino]ethyl, carboxy C1-C4 hydrocarbyl, piperidinyl, 2-pyridinyl, 3-pynidinyl, 4-pyndinyl, sulfonamido, C1-C4 hydrocarbylsulfonyl, C1-C4 hydrocarbylphosphonyl, and —C(O)—W;
• each —W is independently selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy, and —CHR12NH2;
• each R12 is independently selected from the group consisting of a side chain of a D amino acid, a side chain of an L amino acid, benzyloxy, benzylamino, and amino;
• and
• only one of R2, R3, R6, and R7 may be other than hydrido, C1-C4 hydrocarbyl, or a part of a heterocyclic ring structure.

A compound or a salt thereof, wherein:

• the compound corresponds in structure to Formula I:
• R1 is phenyl substituted with R4 at the 4-position;
• and
• R4 is selected from the group consisting of phenyl, phenoxy, thiophenoxy, phenylazo, benzamido, anilino, nicotinamido, isonicotinamido, picolinamido, and phenylureido, wherein any such substituent is optionally substituted:
• at the meta- or para-position or both with a substituent that is selected from the group consisting of halogen, C1-C9 hydrocarbyloxy, C1-C10 hydrocarbyl, di-C1-C9 hydrocarbylamino, carboxyl C1-C8 hydrocarbyl, C1-C4 hydrocarbyloxy carbonyl C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxycarbonyl C1-C4 hydrocarbyl, and carboxamido C1-C8 hydrocarbyl, or
• at the meta- and para-positions by two methyl groups or by a methylenedioxy group;
• as to R2 and R3:
• R3 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R2 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R2 and R3, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring, wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent selected from the group consisting of C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• as to R6 and R7:
• R7 is independently selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R6 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R6 and R7, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent selected from the group consisting of C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• each —Y is independently selected from the group consisting of —O and —NR11;
• each R11 is independently selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• each —Z is independently selected from the group consisting of hydrido, C1-C4 hydrocarbyl, benzoyl, (2-pyridinyl)methyl, (3-pyridinyl)methyl, (4-pyridinyl)methyl, 2-(morpholinyl)ethyl, 2-(piperidinyl)ethyl, 2-(piperazinyl)ethyl, 2-(N-methylpiperazinyl)ethyl, 2-(thiomorpholinyl)ethyl, 2-(thiomorpholinyl sulfone)ethyl, 2-(succinimidyl)ethyl, 2-(hydantoinyl), 2-(3-methylhydantoinyl)ethyl, 2-(N-C1-C4 hydrocarbylamino)ethyl, 2-[N,N-di(C1-C4 hydrocarbyl)amino]ethyl, carboxy C1-C4 hydrocarbyl, piperidinyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl, sulfonamido, C1-C4 hydrocarbylsulfonyl, C1-C4 hydrocarbylphosphonyl, and —C(O)—W;
• each —W is independently selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy, and —CHR12NH2;
• each R12 is independently selected from the group consisting of a side chain of a D amino acid, a side chain of an L amino acid, benzyloxy, benzylamino, and amino;
• and
• only one of R2, R3, R6, and R7 may be other than hydrido, C1-C4 hydrocarbyl, or a part of a heterocyclic ring structure.

A compound or a salt thereof, wherein:

• the compound corresponds in structure to Formula II:
• PhR4 is phenyl substituted at its 4-position with R4;
• R4 is selected from the group consisting of single-ringed aryl, single-ringed heteroaryl, C3-C14 hydrocarbyl, C2-C14 hydrocarbyloxy, phenoxy, thiophenoxy, 4-thiopyridyl, phenylazo, phenylureido, nicotinamido, isonicotinamido, picolinamido, anilino group, and benzamido;
• as to R2 and R3:
• R3 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R2 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R2 and R3, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring, wherein each heteroatom of the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent, R5, that is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• —Y is selected from the group consisting of —O and —NR11;
• R11 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• —Z is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, benzoyl, (2-pyridinyl)methyl, (3-pyridinyl)methyl, (4-pyridinyl)methyl, 2-(morpholinyl)ethyl, 2-(piperidinyl)ethyl, 2-(piperazinyl)ethyl, 2-(N-methylpiperazinyl)ethyl, 2-(thiomorpholinyl)ethyl, 2-(thiomorpholinyl sulfone)ethyl, 2-(succinimidyl)ethyl, 2-(hydantoinyl), 2-(3-methylhydantoinyl)ethyl, 2-(N-C1-C4 hydrocarbylamino)ethyl, 2-[N,N-di(C1-C4 hydrocarbyl)amino]ethyl, carboxy C1-C4 hydrocarbyl, piperidinyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl, sulfonamide, C1-C4 hydrocarbylsulfonyl, C1-C4 hydrocarbylphosphonyl, and —C(O)—W;
• —W is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy, and —CHR12NH2;
• and
• R12 is selected from the group consisting of a side chain of a D amino acid, a side chain of an L amino acid, benzyloxy, benzylamino, and amino.

A compound or a salt thereof, wherein:

• the compound corresponds in structure to Formula II:
• PhR4 is phenyl substituted at its 4-position with R4;
• R4 is selected from the group consisting of phenyl, phenoxy, anilino, thiophenoxy, benzamido, nicotinamido, isonicotinamido, picolinamido, and phenylureido, wherein any such substituent is itself optionally substituted:
• at the meta or para position or both with a substituent that is selected from the group consisting of halogen, C1-C9 hydrocarbyloxy, C1-C10 hydrocarbyl, di-C1-C9 hydrocarbylamino, carboxyl C1-C8 hydrocarbyl, C1-C4 hydrocarbyloxy carbonyl C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxycarbonyl C1-C4 hydrocarbyl, and carboxamido C1-C8 hydrocarbyl;
• at the meta- and para-positions by two methyl groups or by a C1-C2 alkylenedioxy group;
• as to R2 and R3:
• R3 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R2 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R2 and R3, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring, wherein each heteroatom of the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent, R5, that is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• —Y is selected from the group consisting of —O and —NR11;
• R11 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• —Z is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, benzoyl, (2-pyridinyl)methyl, (3-pyridinyl)methyl, (4-pyridinyl)methyl, 2-(morpholinyl)ethyl, 2-(piperidinyl)ethyl, 2-(piperazinyl)ethyl, 2-(N-methylpiperazinyl)ethyl, 2-(thiomorpholinyl)ethyl, 2-(thiomorpholinyl sulfone)ethyl, 2-(succinimidyl)ethyl, 2-(hydantoinyl), 2-(3-methylhydantoinyl)ethyl, 2-(N-C1-C4 hydrocarbylamino)ethyl, 2-[N,N-di(C1-C4 hydrocarbyl)amino]ethyl, carboxy C1-C4 hydrocarbyl, piperidinyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl, sulfonamide, C1-C4 hydrocarbylsulfonyl, C1-C4 hydrocarbylphosphonyl, and —C(O)—W;
• —W is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy, and —CHR12NH2;
• and
• R12 is selected from the group consisting of a side chain of a D amino acid, a side chain of an L amino acid, benzyloxy, benzylamino, and amino.

A compound or a salt thereof, wherein:

• the compound corresponds in structure to Formula VII:
• PhR4 is phenyl substituted at its 4-position with R4;
• R4 is selected from the group consisting of single-ringed aryl, single-ringed heteroaryl, C3-C14 hydrocarbyl, C2-C14 hydrocarbyloxy, phenoxy, thiophenoxy, 4-thiopyridyl, phenylazo, phenylureido, nicotinamido, isonicotinamido, picolinamido, anilino, and benzamido;
• as to R2 and R3:
• R3 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R2 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R2 and R3, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring, wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent, R5, that is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 carbonylhydrocarbyl, and sulfonyl C1-C4 hydrocarbyl;
• —Y is selected from the group consisting of —O and —NR11;
• R11 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• —Z is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, benzoyl, (2-pyridinyl)methyl, (3-pyridinyl)methyl, (4-pyridinyl)methyl, 2-(morpholinyl)ethyl, 2-(piperidinyl)ethyl, 2-(piperazinyl)ethyl, 2-(N-methylpiperazinyl)ethyl, 2-(thiomorpholinyl)ethyl, 2-(thiomorpholinyl sulfone)ethyl, 2-(succinimidyl)ethyl, 2-(hydantoinyl), 2-(3-methylhydantoinyl)ethyl, 2-(N-C1-C4 hydrocarbylamino)ethyl, 2-[N,N-di(C1-C4 hydrocarbyl]amino)ethyl, carboxy C1-C4 hydrocarbyl, piperidinyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl, sulfonamido, C1-C4 hydrocarbylsulfonyl, C1-C4 hydrocarbylphosphonyl and —C(O)—W;
• —W is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy, and —CHR12NH2;
• and
• R12 is selected from the group consisting of a side chain of a D amino acid, a side chain of an L amino acid, benzyloxy, benzylamino, and amino.

A compound or a salt thereof, wherein:

• the compound corresponds in structure to Formula VII:
• PhR4 is phenyl substituted at its 4-position with R4;
• R4 is selected from the group consisting of phenyl, phenoxy, anilino, thiophenoxy, benzamido, nicotinamido, isonicotinamido, picolinamido, and phenylureido, wherein any such substituent is itself optionally substituted:
• at the meta or para position or both with a substituent that is selected from the group consisting of halogen, C1-C9 hydrocarbyloxy, C1-C10 hydrocarbyl, di-C1-C9 hydrocarbylamino, carboxyl C1-C8 hydrocarbyl, C1-C4 hydrocarbyloxy carbonyl C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxycarbonyl C1-C4 hydrocarbyl, and carboxamido C1-C8 hydrocarbyl group, or
• at the meta- and para-positions by two methyl groups or by a C1-C2 alkylenedioxy group;
• as to R2 and R3:
• R3 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• and R2 is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, N-piperidinyl, N-piperazinyl, N-(C1-C4 hydrocarbyl)piperazinyl, N-pyrrolidinyl, N-morpholinyl, and —Y—Z, or
• R2 and R3, together with the depicted carbon atom to which they are bonded, form a 6-membered heterocyclic ring, wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent, R5, that is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 carbonylhydrocarbyl, and sulfonyl C1-C4 hydrocarbyl;
• —Y is selected from the group consisting of —O and —NR11;
• R11 is selected from the group consisting of hydrido and C1-C4 hydrocarbyl;
• —Z is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, benzoyl, (2-pyridinyl)methyl, (3-pyridinyl)methyl, (4-pyridinyl)methyl, 2-(morpholinyl)ethyl, 2-(piperidinyl)ethyl, 2-(piperazinyl)ethyl, 2-(N-methylpiperazinyl)ethyl, 2-(thiomorpholinyl)ethyl, 2-(thiomorpholinyl sulfone)ethyl, 2-(succinimidyl)ethyl, 2-(hydantoinyl), 2-(3-methylhydantoinyl)ethyl, 2-(N-C1-C4 hydrocarbylamino)ethyl, 2-[N,N-di(C1-C4 hydrocarbyl]amino)ethyl, carboxy C1-C4 hydrocarbyl, piperidinyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl, sulfonamido, C1-C4 hydrocarbylsulfonyl, C1-C4 hydrocarbylphosphonyl and —C(O)—W;
• —W is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy, and —CHR12NH2;
• and
• R12 is selected from the group consisting of a side chain of a D amino acid, a side chain of an L amino acid, benzyloxy, benzylamino, and amino.

A process for treating a host mammal having a condition associated with pathological matrix metalloprotease activity, wherein:

• the process comprises administering a compound or a salt thereof in an MMP enzyme-inhibiting effective amount to a mammalian host having such a condition;
• the compound corresponds in structure to Formula I:
• R1 is a substituted 5- or 6-membered cyclohydrocarbyl, heterocyclo, aryl, or heteroaryl;
• the number of non-hydrogen atoms in the longest linear chain of atoms in R1 is greater than 6 and less than about 20 atoms;
• R1 defines a three-dimensional volume, when rotated about an axis drawn through the SO2-bonded 1-position and the 4-position of a 6-membered ring or drawn through the SO2-bonded 1-position and the center of the 3,4-bond of a 5-membered ring, whose widest dimension in a direction transverse to the axis of rotation is about that of one furanyl ring to about that of two phenyl rings;
• as to R2 and R3:
• R2 and R3 are independently selected from the group consisting of hydrido, C1-C4 hydrocarbyl, heteroaryl-C1-C4 hydrocarbyl, aryl-C1-C4 hydrocarbyl, hydroxy-C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy-C1-C4 hydrocarbyl, aryloxy-C1-C4 hydrocarbyl, amino-C1-C4 hydrocarbyl, C1-C4 hydrocarbylthio-C1-C4 hydrocarbyl, C1-C4 hydrocarbylsulfonyl-C1-C4 hydrocarbyl, aminosulfonylamino-C1-C4 hydrocarbyl, aminocarbonylamino-C1-C4 hydrocarbyl, C1-C4 hydrocarbylcarbonylamino-C1-C4 hydrocarbyl, aryl-C1-C4 hydrocarbyl, heteroaryl-C1-C4 hydrocarbyl, and benzyloxy-C1-C4 hydrocarbyl, except that only one of R2 and R3 may be other than hydrido or C1-C4 hydrocarbyl, or
• R2 and R3, together with the depicted carbon atom to which they are bonded, form a heterocyclic ring, wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent, R5, that is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• as to R6 and R7:
• R6 and R7 are independently selected from the group consisting of hydrido, C1-C4 hydrocarbyl, heteroaryl-C1-C4 hydrocarbyl, aryl-C1-C4 hydrocarbyl, hydroxy-C1-C4 hydrocarbyl, C1-C4 hydrocarbyloxy-C1-C4 hydrocarbyl, aryloxy-C1-C4 hydrocarbyl, amino-C1-C4 hydrocarbyl, C1-C4 hydrocarbylthio-C1-C4 hydrocarbyl, C1-C4 hydrocarbylsulfonyl-C1-C4 hydrocarbyl, aminosulfonylamino-C1-C4 hydrocarbyl, aminocarbonylamino-C1-C4 hydrocarbyl, C1-C4 hydrocarbylcarbonylamhio-C1-C4 hydrocarbyl, aryl-C1-C4 hydrocarbyl, heteroaryl-C1-C4 hydrocarbyl, and benzyloxy-C1-C4 hydrocarbyl, except that only one of R6 and R7 may be other than hydrido or C1-C4 hydrocarbyl, or
• R6 and R7, together with the depicted carbon atom to which they are bonded, form a heterocyclic ring, wherein each heteroatom in the heterocyclic ring is:
• independently selected from the group consisting of oxygen, sulfur, and nitrogen,
• when sulfur, optionally substituted with one or two oxygens, and
• when nitrogen, optionally substituted with a substituent, R5, that is selected from the group consisting of hydrido, C1-C4 hydrocarbyl, C3-C6 cyclohydrocarbyl, C1-C4 hydrocarbylcarbonyl, and C1-C4 hydrocarbylsulfonyl;
• and
• only one of R2, R3, R6, and R7 may be other than hydrido, C1-C4 hydrocarbyl, or a part of a heterocyclic ring structure.