Patent ID: 8324174

Claim:
A method for preparing a compound having formula (II), or a pharmaceutically acceptable salt thereof: wherein X is O; R 2 and R 4 are each isobutyl; R 5 is selected from the group consisting of: (i) —NHC(═O)CH 2 OH; (ii) —NHC(═O)CH 2 OP(O)(O − Na + ) 2 ; (iii) —NHC(═O)CH 2 N(CH 3 ) 2 ; (iv) —NHC(═O)CH 2 -(1-piperidyl); (v) —NHC(═O)CH 2 -(cyclopropyl); and (vi) —NHC(═O)CH 2 CH 2 CH 2 N(CH 3 ) 2 ; the method comprising reacting a first compound, or a salt thereof, having a first formula, which is selected from the group consisting of: with a second compound, or a salt thereof, having a second formula: