The previously reported synthesis of 139221 (scheme 13922101a) has been investigated in order to find a more efficient, reproducible and economical route to work in the mutikilogram scale. Herein it is reported a new process which is simpler and proceeds with an overall yield of 54% (the original process, 35%). The condensation of intermediate aminolactone (I) (scheme 13922101a, intermediate (VII)) with acid (XLII) (the acid derived from scheme 13922101a, intermediate ester (IX)) by means of 2-chloro-1,3-dimethylimidazolidinium hexafluorophosphate (CIP), and 1-hydroxy-7-azabenzotriazole (HOAt) in THF/dichloromethane gives the coupling product (XLIII), which is allylated with allyl bromide (XLIV) and Cs2CO3 in DMF yielding the allyl ether (XLV). The reduction of the lactone group of (XLV) with LiAlH2(OEt)2 in ethyl ether affords the lactol (XLVI), which is desilylated with KF in methanol to provide the phenolic compound (XLVII). The opening of the lactol ring of (XLVII) with simultaneous cyclization by means of Tf-OH in water/trifluoroethanol gives the hexacyclic intermediate (XLVIII), which is finally reductocondensed with KCN by means of LiAlH2(OEt)2 in THF to furnish the previously reported pentacyclic intermediate (XI) (scheme 13922101a, intermediate (XI)).

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).

The condensation of benzaldehyde (I) with malonic ester (II) by means of piperidine and acetic acid in benzene gives the unsaturated malonate (III), which by a selective ester cleavage and a Curtius rearrangement by means of N3-PO(OPh)2 and Et3N in toluene yields the unsaturated aminoester (IV). The reduction of (IV) with a chiral rhodium catalyst affords the chiral protected aminoester (V), which is cyclized to the bridged lactone (VI) by means of BF3 ethearate in dichloromethane. Reductive cleavage of the benzyloxycarbonyl benzyl ether groups of (VI) with H2 over Pd/C affords the free aminophenol (VII). The condensation of (VII) with aldehyde (VIII) (obtained by reduction of ester (IX) with DIBAL in dichloromethane) by means of KCN and AcOH, and after allylation of the aromatic OH group with allyl bromide, the intermediate (X) is obtained. The reduction of the lactone group of (X) with DIBAL, followed by desilylation with KF and cyclization with CH3SO3H affords the polycyclic compound (XI).

The selective trifluoromethanesulfonation of the least hindered phenolic OH group of (XI) with Tf2NPh, TEA and DMAP gives monosulfonate (XII), which is selectively silylated at the primary OH group with TBDPSCl yielding silyl ether (XIII). The protection of the last OH group of (XIII) with Mom-Br and DIEA affords the fully protected intermediate (XIV), which is deallylated with Bu3SnH and PdCl2(PPh3)2 to give the intermediate (XV). The reductive methylation of the NH group of (XV) with formaldehyde and NaBH3CN yields the N-methyl derivative (XVI). The replacement of the CF3SO3 group of (XVI) by methyl is performed by treatment with Me4Sn and PdCl2(PPh3)2 in hot DMF provides the phenol (XVII), which is oxidized with (PhSeO)2O and desilylated with TBAF to give the dihydroxydienone (XVIII).

The esterification of the primary OH group of (XVIII) with the protected cysteine (XIX) by means of EDC and DMAP in dichloromethane gives ester (XX), which is cyclized by means of trifluoromethanesulfonic anhydride and DMSO yielding the bridged lactone (XXI). The oxidation of (XXI) with N-methylpyridinium-4-carbaldehyde (NMPA), DBU and PdCl2(PPh3)2 affords the oxolactone (XXII), which is finally cyclized with 2-(3-hydroxy-4-methoxyphenyl)ethylamine (XXIII) by means of TFA and AgNO3 in water.

6-(Benzyloxy)-7-methyl-1,3-benzodioxole-5-carbaldehyde (scheme 13922101a, cp. (I)). The protection of the OH group of phenol (XXIV) with Mom-Br and NaH in DMF/ethyl ether gives the methoxymethyl ether (XXV), which is methylated with MeI and BuLi in hexane yielding the 4-methyl derivative (XXVI). The formylation of (XXVI) with n-BuLi and DMF in THF affords the carbaldehyde (XXVII), which is deprotected with MsOH in dichloromethane giving 6-hydroxy-7-methyl-1,3-benzodioxole-5-carbaldehyde (XXVIII). Finally, this compound is benzylated with benzyl bromide and NaH in DMF providing the desired intermediate (I).

Malonic acid allyl, 2,2-dimethoxyethyl diester (scheme 13922101a, cp. (II)). The reaction of allyl acetate (XXIX) with LDA and CO2 in ethyl ether gives the malonic acid monoallyl ester (XXX), which is then esterified with 2,2-dimethoxyethanol (XXXI) by means of BOP-Cl and TEA in dichloromethane to afford the desired intermediate (II).

(S)-2-(Allyloxycarbonylamino)-3-[4-methoxy-3,5-bis(tert-butyldimethylsilyloxy)phenyl]propionic acid methyl ester (scheme 13922101a, cp. (IX)). The silylation of 3,5-dihydroxy-4-methoxybenzoic acid methyl ester (XXXII) with TBDMS-Cl, TEA and DMAP in dichloromethane gives the silylated compound (XXXIII), which is reduced with DIBAL in dichloromethane yielding the corresponding benzyl alcohol (XXXIV). The oxidation of (XXXIV) with pyridinium dichromate (PDC) in dichloromethane affords the benzaldehyde (XXXV), which is condensed with malonic acid monomethyl ester (XXXVI) by means of piperidine/AcOH in toluene providing the corresponding benzylidene derivative (XXXVII). The reaction of (XXXVII) with (PhO)2PO-N3 and benzyl alcohol in hot toluene affords the benzyloxycarbonylamino derivative (XXXVIII), which is enantioselectively reduced with H2 over a chiral Rh catalyst in methanol providing and (S)-2-(benzyloxycarbonylamino)-3-[4-methoxy-3,5-bis(tert-butyldimethylsilyloxy)phenyl]propionic acid methyl ester (XXXIX). Elimination of the benzyl protecting group of (XXXIX) with H2 over Pd/C in ethyl acetate gives the free aminoester (XL), which is finally reprotected with allyl chloroformate (XLI) and pyridine to furnish the desired intermediate (IX).

Synthesis of the amine intermediate (VIII): The condensation of 1,3-benzodioxole (I) with the didehydro morpholinone (II) by means of TFA in dichloromethane gives the chiral adduct (III), which is treated with Tf2O and pyridine in dichloromethane to yield the triflate (IV). The reductive cleavage of (IV) by means of NaBH4 in methanol affords the aminodiol (V), which is selectively monosilylated at the primary OH group with Tbdps-Cl and imidazole to provide the silyl ether (VI). The reaction of the triflate group of (VI) with MeZnCl and PdCl2(dppf) in refluxing THF gives the methylated compound (VII), which is treated with Pb(OAc)4 and NH2OH in ethanol to afford the target primary amine intermediate (VIII).

Synthesis of the iodo-L-phenylalanine intermediate (XVII): The condensation of catechol derivative (IX) with methyl orthoformate by means of BuLi and CSA in methanol gives the benzaldehyde dimethyl acetal (X), which is iodinated with I2 and BuLi in ethyl ether to yield the iodobenzaldehyde acetal (XI). The hydrolysis of the acetal group of (XI) by means of HCl in THF affords the 3-hydroxy benzaldehyde derivative (XII), which is treated with benzyl bromide and K2CO3 in refluxing acetonitrile to provide the benzyl protected benzaldehyde derivative (XIII). The Horner-Emmons condensation of aldehyde (XIII) with phosphonate (XIV) by means of TMG in dichloromethane gives the dehydrophenylalanine derivative (XV), which is submitted to an asymmetric hydrogenation with H2 over a chiral Rh catalyst in hot ethyl acetate to yield the L-enantiomer (XVI). Finally, the ester group of (XVI) is hydrolyzed with LiOH in methanol/water to afford the target iodo-L-phenylalanine intermediate (XVII).

The condensation of the amine intermediate (VIII) with iodo-L-phenylalanine intermediate (XVII), 4-methoxyphenyl isocyanide (XVIII) and acetaldehyde (XIX) in refluxing methanol gives the adduct (XX), which is desilylated with TBAF in THF and acylated with Ac2O and pyridine to yield the acetoxy derivative (XXI). Elimination of the Mom and Boc protecting groups of (XXI) by means of TFA in dichloromethane affords the aminophenol (XXII), which is submitted to cyclization in refluxing ethyl acetate to provide the piperazinedione derivative (XXIII). The reaction of the OH group of (XXIII) with MsCl and pyridine in dichloromethane and the piperazine NH with Boc2O and DMAP in acetonitrile gives the fully protected compound (XXIV), which is reduced with NaBH4 in EtOH/dichloromethane and dehydrated by means of CSA and quinoline in refluxing toluene to yield the tetrahydropyrazinone (XXV). The cyclization of (XXV) by means of Pd2(dba)3, P(o-tol)3 and TEA in refluxing acetonitrile affords the tricyclic compound (XXVI).

The hydrolysis of the mesylate group of (XXVI) with NaOH in refluxing MeOH/water, followed by reaction with Ac2O and pyridine gives the diacetate (XXVII). The cleavage of the Boc group of (XXVII) by means of TFA in dichloromethane, followed by reprotection with Troc-Cl and NaHCO3 in dichloromethane yields the expected compound (XXVIII). The reaction of (XXVIII) with dimethyldioxirane and CSA in MeOH/acetone affords the acid-sensitive epoxide (XXIX), which, without isolation, is treated with MeOH and CSA to provide the methoxy alcohol (XXX). The reduction of (XXX) with NaBH3CN and TFA provides the chiral alcohol (XXXI) as a single isomer, which is protected with Tbdms-Cl and imidazole to give the silyl ether (XXXII). Cleavage of the Ac groups of (XXXII) by means of guanidinium nitrate and NaOMe in methanol/dichloromethane yields the dihydroxy compound (XXXIII).

The selective protection of the phenolic OH of (XXXIII) by means of benzyl bromide and K2CO3 in refluxing acetonitrile gives the benzyl ether (XXXIV), which is reductocyclized by means of Red-Al in THF to yield the oxazolidine (XXXV). The cleavage of the oxazolidine ring of (XXXV) by means of Tms-CN and BF3/Et2O in dichloromethane affords the hydroxy nitrile (XXXVI), which is treated with Ac2O and pyridine to provide the acetate (XXXVII). The desilylation of (XXXVII) with HF in acetonitrile, followed by oxidation with DMP gives the carbaldehyde (XXXVIII), which is submitted to hydrogenolysis of the benzyl ethers by means of H2 over Pd/C in THF, performing a simultaneous cyclization to yield the pentacyclic compound (XXXIX). The reaction of (XXXIX) with allyl bromide (XL) and DIEA affords the allyl ether (XLI), which is treated with K2CO3 in methanol to provide the carbinol (XLII). The reaction of (XLII) with L-cysteine derivative (XLIII) by means of WSCD and DMAP in dichloromethane gives the corresponding ester (XLIV).

Cleavage of the thioacetate bond of (XLIV) by means of hydrazine yields the thiol (XLV), which is cyclized by means of TFA in trifluoroethanol under high dilution conditions to afford the macrocyclic compound (XLVI). The reaction of (XLVI) with Ac2O and pyridine provides the acetate (XLVII), which is treated with Zn and HOAc in ethyl ether to eliminate the troc-protecting group, yielding (XLVIII). The reductive methylation of the NH group of (XLVIII) by means of HCHO, NaBH3CN and HOAc in methanol affords the N-methylamine derivative (XLIX), whose Alloc and ally ether groups are simultaneously eliminated by treatment with PdCl2(PPh3)2 and Bu3SnH in dichloromethane to provide the aminophenol (L). The transamination reaction of (L) with 4-formyl-1-methylpyridinium benzenesulfonate (FMPBS) and DBU in DMF/dichloromethane gives the alpha-ketolactone (LI).

The Pictet-Spengler cyclization of (LI) with 2-(3-hydroxy-4-methoxyphenyl)ethylamine (LII) by means of NaOAc in ethanol yields the spiro-tetrahydroisoquinoline (LIII). Finally, the nitrile group of (LIII) is treated with AgNO3 in acetonitrile/water to afford the target Ecteinascidin 743.