A compound which is of formula I: where R is selected from the group consisting of: where the * indicates the point of attachment of R to the remainder of the molecule; R 1, R 2, and R 3 are independently selected from the group consisting of hydrogen and C 1 -C 6 -alkyl; R 4 is C 1 -C 6 -alkyl; R 5 and R 6 are independently selected from the group consisting of hydrogen, hydroxy, alkoxy, C 1 -C 40 -alkyl, C 1 -C 40 -alkenyl, C 1 -C 40 -alkynyl, and aryl; where the alkyl, alkenyl, alkynyl, or aryl groups are optionally substituted with -OR 10, -S 0-2 R 10, -CN, -F, -Cl, -Br, -I, -NR 10 R 10', oxo, C 3 -C 6 -cycloalkyl, aryl, aryl-C 1 -C 6 -alkyl, heteroaryl, heterocyclyl, -C -R 11, -C -C 0 -C 6 -alkyl-aryl, -C -OR 11, -C -O-C 0 -C 6 -alkyl-aryl, -C -N-R 11 R 11', -C -NH-C 0 -C 6 -alkyl-aryl, -NH-C -R 11, or -NH-C -C 0 -C 6 -alkyl-aryl; where the aryl, heteroaryl and heterocyclyl ring substituents are optionally further substituted with C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl, oxo, hydroxy, C 1 -C 6 -alkoxy, -C -C 1 -C 6 -alkyl, or -C -O-C 1 -C 6 -alkyl; and where one of the carbons of the alkyl, alkenyl, or alkynyl groups is optionally substituted with a heteroatom selected from the group consisting of -O-, -N- and -S-; or R 5 and R 6 together with the atom to which they are attached form a saturated or unsaturated 3-8 membered ring, optionally incorporating 1, 2, or 3 additional N, O, or S atoms, optionally substituted with oxo, -OR 10, -SR 10, -CN, -F, -Cl, -Br, -I, -NR 10 R 10', C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl, hydroxy-C 1 -C 6 -alkyl-, -C -H, -C -C 1 -C 6 -alkyl, -C -aryl, -C -OH, or -C -O-C 1 -C 6 -alkyl; or R 5 and R 6 together with the nitrogen atom to which they are attached form a N,N'- disubstituted piperazine where the nitrogen substitution at the 4-position is a group identical to the substitution at the 1-position forming a compound of formula Iaa or Ibb, where R 1, R 2, R 3, and R 4 are as defined above: R 10 and R 10' are independently selected from the group consisting of hydrogen, C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl, aryl, aryl-C 1 -C 6 -alkyl, heteroaryl, heterocyclyl, -C -H,-C -C 1 -C 6 -alkyl, -C -aryl, and -C -C 1 -C 6 -alkyl-aryl; R 11 and R 11' are selected from the group consisting of hydrogen and C 1 -C 6 -alkyl; and M and M' are independently selected from the group consisting of hydrogen, -C -R 12 -C -C 1 -C 6 -alkenyl, -C -C 1 -C 6 -alkynyl, -C -aryl, -C -heteroaryl, -C O-R 12, -C NR 12 R 12, -SO 2 OR 12, -SO 2 -C 1 -C 6 -alkyl, -SO 2 -haloC 1 -C 6 -alkyl, -SO 2 -aryl, -SO 2 -NR 12 R 12, -P (OR 12)(OR 12), and C-linked mono or di-peptide, where R 12 is hydrogen or C 1 -C 6 -alkyl optionally substituted with -OH, -NH 2, -NH(C 1 -C 4 alkyl), -N(C 1 -C 4 alkyl) 2,-C -OH, -C -O-C 1 -C 4 -alkyl, or halogen; or a salt, a stereoisomer, or a mixture of stereoisomers thereof. where the * indicates the point of attachment of R to the remainder of the molecule; R 1, R 2, and R 3 are independently selected from the group consisting of hydrogen and C 1 -C 6 -alkyl; R 4 is C 1 -C 6 -alkyl; R 5 and R 6 are independently selected from the group consisting of hydrogen, hydroxy, alkoxy, C 1 -C 40 -alkyl, C 1 -C 40 -alkenyl, C 1 -C 40 -alkynyl, and aryl; where the alkyl, alkenyl, alkynyl, or aryl groups are optionally substituted with -OR 10, -S 0-2 R 10, -CN, -F, -Cl, -Br, -I, -NR 10 R 10', oxo, C 3 -C 6 -cycloalkyl, aryl, aryl-C 1 -C 6 -alkyl, heteroaryl, heterocyclyl, -C -R 11, -C -C 0 -C 6 -alkyl-aryl, -C -OR 11, -C -O-C 0 -C 6 -alkyl-aryl, -C -N-R 11 R 11', -C -NH-C 0 -C 6 -alkyl-aryl, -NH-C -R 11, or -NH-C -C 0 -C 6 -alkyl-aryl; where the aryl, heteroaryl and heterocyclyl ring substituents are optionally further substituted with C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl, oxo, hydroxy, C 1 -C 6 -alkoxy, -C -C 1 -C 6 -alkyl, or -C -O-C 1 -C 6 -alkyl; and where one of the carbons of the alkyl, alkenyl, or alkynyl groups is optionally substituted with a heteroatom selected from the group consisting of -O-, -N- and -S-; or R 5 and R 6 together with the atom to which they are attached form a saturated or unsaturated 3-8 membered ring, optionally incorporating 1, 2, or 3 additional N, O, or S atoms, optionally substituted with oxo, -OR 10, -SR 10, -CN, -F, -Cl, -Br, -I, -NR 10 R 10', C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl, hydroxy-C 1 -C 6 -alkyl-, -C -H, -C -C 1 -C 6 -alkyl, -C -aryl, -C -OH, or -C -O-C 1 -C 6 -alkyl; or R 5 and R 6 together with the nitrogen atom to which they are attached form a N,N'- disubstituted piperazine where the nitrogen substitution at the 4-position is a group identical to the substitution at the 1-position forming a compound of formula Iaa or Ibb, where R 1, R 2, R 3, and R 4 are as defined above: R 10 and R 10' are independently selected from the group consisting of hydrogen, C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl, aryl, aryl-C 1 -C 6 -alkyl, heteroaryl, heterocyclyl, -C -H,-C -C 1 -C 6 -alkyl, -C -aryl, and -C -C 1 -C 6 -alkyl-aryl; R 11 and R 11' are selected from the group consisting of hydrogen and C 1 -C 6 -alkyl; and M and M' are independently selected from the group consisting of hydrogen, -C -R 12 -C -C 1 -C 6 -alkenyl, -C -C 1 -C 6 -alkynyl, -C -aryl, -C -heteroaryl, -C O-R 12, -C NR 12 R 12, -SO 2 OR 12, -SO 2 -C 1 -C 6 -alkyl, -SO 2 -haloC 1 -C 6 -alkyl, -SO 2 -aryl, -SO 2 -NR 12 R 12, -P (OR 12)(OR 12), and C-linked mono or di-peptide, where R 12 is hydrogen or C 1 -C 6 -alkyl optionally substituted with -OH, -NH 2, -NH(C 1 -C 4 alkyl), -N(C 1 -C 4 alkyl) 2,-C -OH, -C -O-C 1 -C 4 -alkyl, or halogen;