L Carnitine vs Acetyl L Carnitine: Key Differences L carnitine is primarily synthesized in the liver from the amino acids lysine and methionine through a series of four enzymatic reactions, with the liver and kidneys converting the precursor butyrobetaine into active Amazon.com: Alpha Lipoic Acid 600mg N Acetyl Cysteine 600mg Acetyl L Carnitine 500mg Benfotiamine 300mg Nerve Support Supplement for Women and Men with Vitamin B1 B6 & B12 Made in USA 90 NAC (N Acetyl L Cysteine)