High quantities of the ethyl ester 22 were found in the worms treated with this compound, while lower quantities of the acid 15 were found in the worms treated with 15 (Figure ). Interestingly, a similar amount of the acid 15 was also observed in the worms treated with the ester 22, indicating that it can be converted from the ester to the acid in the worm. However, some ester hydrolysis was also seen in media alone (Figure ). These data confirm the high worm permeability of the ethyl ester 22 and demonstrate that it is possible for this compound to be converted to the corresponding acid 15. Using this approach, it was also shown that OXFBD03 (2) is rapidly deacetylated to give OXFBD02 (1) in media in the presence or absence of worms. As both 1 and 2 have similar affinities for SmBRD3 (1,2) this does not affect the ability of the compound to interact with this protein once in the parasite.