Patent ID: 6916958

Claim:
A compound of the following formula: wherein: R 1 is selected from the group consisting of alkyl (C 1 to C 20 ), aminoalkyl (C 1 to C 20 ) and cycloalkyl (C 3 to C 20 ); R 2 and R 3 are the same or different and are selected from the group consisting of hydrogen, alkyl (C 1 to C 20 ), aminoalkyl (C 1 to C 20 ) and cycloalkyl (C 3 to C 20 ); R 4 is selected from the group consisting of alkyl (C 1 to C 20 ), aminoalkyl (C 1 to C 20 ) and cycloalkyl (C 3 to C 20 ); and X is selected from the group consisting of alkyl (C 2 to C 10 ) and alkyl (C 2 to C 10 ) substituted with cycloalkyl (C 3 to C 20 ); or a pharmaceutically acceptable salt thereof.