The powerful olefin metathesis reaction was employed for the construction of late-phase clinical agents SB1317 and SB1518. In both cases RCM seems to proceed only in the presence of an acid and to predominantly furnish trans isomers. In case of SB1518 it proceeded in the presence of acid HCl, while for SB1317, it mainly proceeds in the presence of TFA (trifluroacetic acid).