It is actually replaced at R1 by using a pentyl chain. The indole core is substituted at R3 with a carbonyl group and that is also linked to a naphthalene moiety.Also, the indole Main is substituted at R3 that has a carbonyl group that's also bonded into a napthalene moeity. Napthalene can be a bicyclic construction of two fused benzene rings. This