L-alloisoleucine (2S, 3R), a diastereomer of L-isoleucine (2S, 3S), is a normal constituent of human plasma. It was shown, that the plasma L-alloisoleucine above the cutoff value of 5 micromol/L is the most specific and most sensitive diagnostic marker for all forms of maple syrup urine disease (MSUD). The precise mechanism of L-alloisoleucine formation is unclear, but existed suggestions, that R-3-methyl-2-oxopentanoate is an immediate and inevitable byproduct of L-isoleucine transamination and that alloisoleucine is primarily formed via transamination of 3-methyl-2-oxopenanoate in vivo.

CGP-71683A is a non-peptidic neuropeptide Y (NPY) Y5 receptor antagonist that was under development by Novartis. CGP-71683A is an extremely selective, non-peptide NPY Y5 receptor antagonist, displaying > 1000-fold selectivity over Y1, Y2 and Y4 receptors; IC50 values are 1.4, 2765, 7187 and 5637 nM at cloned rat Y5, Y1, Y2 and Y4 receptors respectively. CGP-71683A potently inhibits NPY-induced food intake following i.p. administration in diabetic, free-feeding and fasted rats.