<unk>  is a product of the lysis of cystathionine.
It is also one of the degradation products of threonine.
It can be converted to propionyl-CoA (and subsequently methylmalonyl CoA, which can be converted to succinyl CoA, a CAC intermediate), and thus enter the citric<unk>  cycle.
Alpha-ketobutyric acid
Gamma-amino-beta-hydroxybutyric acid
Gamma-aminobutyric acid
Glycocyamine
Choline
Acetylcholine
Glutamine
Dopamine