"合酯" seems to make sense here, which is called "ester" in English (You may find an example here http://www.wekenchem.com/pages/Gatifloxacin_Intermediate-c.h... & http://cypharm.cn.chemnet.com/show/pdetail--1054333.html), and "丙酸盐" is called "propionate". So the whole term could be "propionate ester". This is a reference, and you may have to check with the chemical structure to see if the so called "propionate ester" matches the chemicals indicated in your source.