The reaction of cyclopeptide (V) with 2-sulfanylethylamine (VI) by means of camphorsulfonic acid (CSA) in DMF gives the epi-2-aminoethylsulfanyl compound (VII), which is oxidized with oxone in acetonitrile/water, affording the sulfone (VIII). Finally, this compound is treated with ethylenediamine in DMF to afford the target compound.
The reaction of cyclopeptide (I) with phenylboronic acid in THF gives the bis boronate (II), which is reduced at the carbamoyl group with BH3/S(Me)2 in THF and deprotected with HCl to afford the cyclopeptide (III). The reaction of (III) with thiophenol and TFA in acetonitrile affords the phenylsulfanyl derivative (IV), which is finally treated with ethylenediamine to afford the target compound. Alternatively, cyclopeptide (I) can be reduced directly to cyclopeptide (II) with BH3/S(Me)2 in THF.