A review. Science has unveiled tricks hidden in the unique chem. structures and biol. activities of naturally occurring compounds Triggered by these findings, scientists have discovered substances and developed them into new drugs, which have been used in the mid 20th century and beyond to cure the sick. The author recalls his educational research experiences in the chem. synthesis of kanamycin, an antibiotic, in the isolation and structural determination of aplysiatoxin, a marine toxin, and in his corporate research and development of drugs with active forms of vitamin D from the 1960s to the 1980s. Biol. active natural products from marine sources often have highly complex structures. He hopes that in the 21st century the highly advanced organic syntheses will play a key role in the discovery and development of new drugs from marine natural products to treat unmet needs.