[gmx-users] Generating topology for Tetrahydrofolate within CHARMM ff

[zeineb SI CHAIB]

Dear gmx users, 

I'm working on simulating a protein with two cofactors (hem and tetrahydrofolat) and its substrate. I'm in the first stage; generating topology. I choose CHARMM27 as a force field and I'm little bit confused on how to generate tetrahydrofolate's topology. 

I tried the online tool of SwissParam but it doesn't work, although it worked with the substrate ( an amino-acide). 
Failure message: "Unfortunately, topology and parameters were not successfully generated for THG."

Is there any other tools that I can use? Are they reliable? In other words: what are my options (pros and cons of each server/method?).

Thank you in advance for your help. 

Regards. 

Zeineb