Of course organic synthesis is needed to make drug candidates and optimize leads. That is not really the intellectual content of medicinal chemistry. Medicinal chemistry involves many topics not covered in organic chemistry: diversity oriented synthesis, bio-orthogonal chemistry, biophysical methods, bioisosteres, peptidomimetic chemistry to name a few. These topics now constitute a significant chunk of scientific knowledge, and are generally not covered in the undergraduate curriculum. The students in my Medicinal Chemistry course (Jrs and Srs, mostly Biochem majors) find the topic to be extremely interesting, but they have no previous exposure to the core ideas in modern drug development. That is why I think an Open, living textbook would be of interest.