I worked on telaprevir and I found a paper that says that it converts spontaneously to its sterioisomer VRT-127394 in culture. and the reverse also occurs (from VRT-127394 to telaprevir). so is there a way to prevent this.
It depends on which isomer is thermodyanamically more stable. Temperature control may be useful. Use of solvents which preferentially stabilises one or the other isomer by specific interactions may also be helpful.