4-isopropylcatechol has been known as a potent depigmenting agent for more than 35 years. Like other phenolic compounds, it is a tyrosinase inhibitor. In a study done in the early 1970s, most of the melasma patients treated showed skin irritation, and atopic dermatitis. Yet two-thirds also showed significant improvement (5). Due to its specific mechanism of action targeting melanocytes, it has promise for use in melanoma and melasma patients (6-8).
N-Acetyl-4-S-Cystalminylphenol (NA-CAP)
N-acetyl-4-S-cystalminylphenol (NA-CAP) is one of the four known synthesized phenolic thioether amines that are tyrosine-amine derivative analogues. Their toxicity is tyrosinase dependent and targets only melanocytes. This makes NA-CAP, a promising antimelanoma and anti-melasma medication (9). In vitro and in vivo studies of NA-CAP have demonstrated its selective melanocytotoxic and antimelanoma effects (10,11), particularly in the selective disintegration of melanocytes in black hair and skin. NA-CAP is more stable than catechols, and its toxicity appears after oxidation by tyrosinase. A small study showed its efficacy in melasma patients (12). Due to the fact that it is less irritating than hydroquinone, this phenolic thioether known for 20 years is a promising stable molecule for use in melasma patients.