Again, 'Natural Medicinal Chemistry' is a direct translation. However, this course is more commonly called 'Natural Products Chemistry'.

I know the title doesn't mention '药', but this branch of Chemistry - 'Natural Products Chemistry' is referred to the study of the chemical, biological and pharmacological properties of natural products.

References:
1. A natural product is a chemical compound or substance produced by a living organism - found in nature that usually has a pharmacological or biological activity for use in pharmaceutical drug discovery and drug design.
http://en.wikipedia.org/wiki/Natural_product

2. (Chem.) That branch of chemistry which deals with the isolation, identification, structure elucidation, and study of the chemical characteristics of chemical substances produced by living organisms.
http://www.thefreedictionary.com/Natural product chemistry

3. STUDIES IN NATURAL PRODUCTS CHEMISTRY, 32
Description
Natural Product Chemistry continues to expand to exciting new frontiers of great importance in medicine...
http://www.elsevier.com/wps/find/bookdescription.cws_home/70...