The alkylation of thiosemicarbazide (I) with methyl iodide in hot ethanol gives the corresponding S-methyl derivative (II), which is treated with pentylamine (III) in refluxing methanol to yield N1-amino-N3-pentylguanidine hydroiodide (IV). Finally, this compound is condensed with 5-methoxy-1H-indole-3-carbaldehyde (V) by means of HCl in methanol.