Which of the following is NOT a focus of medicinal chemistry?

The focus of medicinal chemistry primarily lies in the design, development, and evaluation of pharmaceutical agents. This involves understanding the chemical properties and biological interactions of compounds that can lead to the creation of effective medications.

The emphasis on chemical synthesis of compounds is crucial, as medicinal chemists are responsible for developing new chemical entities that can serve as potential drugs. Drug design principles are integral to the field because they involve the strategic planning and design of molecules that can interact effectively with biological targets. Additionally, the development of pharmaceutical agents is a core aspect of medicinal chemistry, encompassing everything from the initial concept to the characteristics that make a compound a viable drug candidate.

Clinical trial enrollment procedures, however, fall outside the realm of medicinal chemistry. This area is more specifically related to clinical research and regulatory affairs, focusing on how to enroll participants for trials, maintaining ethical standards, and ensuring compliance with regulations during clinical development. Thus, this is the correct answer as it does not align with the key responsibilities and activities involved in medicinal chemistry.