Reaction of cyanosafracin B (I) with Boc2O in ethanol gives the amino-protected compound (II), which is treated with methoxymethyl bromide (MOM-Br), DIEA and DMAP in acetonitrile yielding the O-protected compound (III). The demethylation of (III) with NaOH in methanol affords the hydroxyquinone (IV), which is reduced with H2 over Pd/C and cyclized with bromochloromethane and Cs2CO3 in hot DMF to provide compound (V). Reaction of (V) with allyl bromide (VI) and Cs2CO3 in DMF gives the allyl ether (VII), which first is treated with TFA, phenyl isothiocyanate and HCl to yield the primary amine (VIII) and then protected at the free NH2 group with Troc-Cl and pyridine, to afford the amino protected compound (IX).
Reaction of (IX) with MOM-Br and DIEA as before affords the ether (X), which is treated with Zn/HOAc in order to regenerate the primary amino group giving (XI). The reaction of (XI) with NaNO2 and HOAc eliminates the NH2 group, affording the primary alcohol (XII), which is esterified with the protected (S)-cysteine (XIII) by means of EDC and DMAP in dichloromethane furnishing the cysteine ester (XIV). Reaction of (XIV) with Bu3SnH and PdCl2(PPh3)2, followed by oxidation with (PhSeO)2O in dichloromethane gives the hydroxyketone (XV), which is cyclized with Tf2O and Ac2O yielding the heptacyclic compound (XVI). Elimination of the MOM protecting group with TMSCl and NaI in CH3CN/CH2Cl2 affords the phenolic compound (XVII).
Intermediate (XVII) by a treatment with Zn and HOAc eliminates the Troc protecting group, giving the primary amine (XVIII). This compound by treatment with 4-formyl-1-methylpyridinium iodide (NMPC), DBU and oxalic acid in order to convert the nitrile group into an alcohol, provides compund (XIX), which is finally cyclized with 2-(3-hydroxy-4-methoxyphenyl)ethylamine (XX) by means of SiO2 / EtOH, followed treatment with and AgNO3 in acetonitrile/water.
The reaction of cyanosafracin B (I) with Boc2O in ethanol gives the amino protected compound (II), which is treated with Mom-Br, DIEA and DMAP in acetonitrile yielding the O-protected compound (III). The demethylation of (III) with NaOH in methanol affords the hydroxyquinone (IV), which is reduced with H2 over Pd/C and cyclized with bromochloromethane and Cs2CO3 in hot DMF providing the methylenedioxy compound (V). The reaction of (V) with acetyl chloride and pyridine in dichloromethane gives the acetate (VI), which is treated with TFA, phenyl isothiocyanate and HCl yielding the primary amine (VII). Finally, this compound is treated with phthalic anhydride (VIII) and CDI in dichloromethane to afford the target phthalimide (phthalascidin Pt-650).