This document summarizes research from several publications investigating compounds that act on serotonin, dopamine, opioid, and calcium receptor systems. It describes the synthesis and evaluation of analogs of aporphine, an alkaloid, examining their effects on serotonin and dopamine receptors. It also discusses the development of opioid receptor agonists and antagonists through stereospecific synthesis and evaluation of derivative compounds. Finally, it mentions the development of cinacalcet and other calcium sensing receptor modulators for the treatment of hyperparathyroidism.