Have you purified it? Betulinic acid should be soluble in CDCl3. As for removing Pyridine rests, one could add small volumes of Toluene (e.g., 3 times) and co-evaporate at reduced pressure.

You can also use deuterated DMSO, however, getting back your sample might be complicated because DMSO is difficult to evaporate.

Anyway, it really work (https://www.researchgate.net/publication/236172806_High_resolution_HPLC_biological_profiling_for_the_rapid_identification_of_antifungal_compounds_in_plants_from_French_Polynesia?ev=prf_pub).

CDCl3 should also work.

Conference Paper High resolution HPLC biological profiling for the rapid iden...

Try in deuterated chloroform. It should be sufficiently soluble to run NMR experiments.

Dear Haoxin,

Try with DMSO or DMF. Also check with THF.All the best.

Similar class of products should be soluble in CDCl3

I've worked with betullinic acid and I also had solubility issues. I had to make the methyl ester derivative using Diazald but there are easier methods of protecting the carboxylic group. The methylated betullinic acid was very soluble in CDCl3, etc. and my spectra looked great. The NMR data for the methylbetulinate is well documented in the literature.

I used cdcl3

Deuterated THF or Pyridine are the best solvents for dissolving betulinic acid. If you want to get rid of the pyridine, just coevaporate your sample three times with toluene and put it on high vacuum overnight. Good luck!

Betulinic acid dissolves in DMSO. The best way is to leave it in DMSO overnight to see good solubility for NMR.

dear  friend  , I am also working on Betulin and betulinic acid , its better to dissolve your sample in dichloomethane and methanol 1:1 ,or gradual decreasing/increasing  ratio  , i m sure u vl get  positive result .

best regard from India