The reaction of S-methylisothiourea (I) with Boc2O by means of NaHCO3 gives the N-Boc protected isothiourea (II), which is condensed with 1,4-butanediamine (III) in hot THF to yield the guanidine derivative (IV). The acylation of the amino group of (IV) with 3,4-dimethoxycinnamoyl chloride (V) with THF/DMF affords the corresponding amide (VI), which is deprotected with TFA to provide N-(4-guanidinobutyl)-3,4-dimethoxycinnamamide (VII). Finally, the guanidino group of (VII) is alkylated with 3-methyl-2-butenyl bromide (VIII) catalyzed by DMAP in THF to provide the target, caracasanamide.

The condensation of 3,4-dimethoxy-N-(4-aminobutyl)cinnamamide (I) with N,N'-bis(tert-butoxycarbonyl)-S-methyl-N-(3-methyl-2-butenyl)isothiourea (II) gives the protected target compound (III), which is finally deprotected by treatment with methanesulfonic acid.