The difference between Folic Acid and Folate. There are cases when taking a synthetic supplement can yield more benefit than a natural one. For example, Acetyl-L-Carnitine is a synthesised version of L-Carnitine, which is a derivative of the amino acids lysine and methionine. Acetyl-L-Carnitine is more bioavailable than L-Carnitine because it easily crosses the blood-brain barrier and delivers L-Carnitine across cell membranes (which it would not be able to cross on its own).