Lead Diversification at the Nanomole Scale Using Liver Microsomes and Quantitative Nuclear Magnetic Resonance Spectroscopy: Application to Phosphodiesterase 2 Inhibitors

In this report, we
describe a method whereby lead molecules can
be converted into several new analogues each using liver microsomes.
Less than one micromole of substrate is incubated with liver microsomes
(mouse, rat, hamster, guinea pig, rabbit, dog, monkey, or human) to
produce multiple products which are isolated and analyzed by quantitative
cryomicroprobe NMR (qNMR) spectroscopy. The solutions from qNMR analysis
were then used as stocks that were diluted into biochemical assays.
Nine human phosphodiesterase-2 (PDE2) inhibitors yielded 36 new analogues.
Products were tested for PDE2 inhibition, intrinsic clearance in human
hepatocytes, and membrane permeability. Two of the products (2c and 4b) were 3–10× more potent
than their respective parent compounds and also had improved metabolic
stability. Others offered insights into structure−activity
relationships. Overall, this process of using liver microsomes at
a submicromole scale of substrate is a useful approach to rapid and
cost-effective late-stage lead diversification.