合成路线1

The reaction of 3-bromopropionic acid (I) with triphenylphosphine (II) in refluxing acetonitrile gives (2-carboxyethyl)-triphenylphosphonium bromide (III), which by a Wittig reaction with 2-oxa-3-hydroxy-6-syn-(3alpha-tetrahydropyranyloxy-4,4-dimethyl-1-trans-octen-1-yl)-7-anti-tetrahydropyranyloxybicyclo- [3.3.0]cis-octane (IV) (prepared according to reference 2) by means of sodium dimethylsulfinate in DMSO yields 9alpha-hydroxy-11alpha,15alpha-bis(tetrahydropyranyloxy)-16,16-dimethyl-alpha-dinorprosta-5-cis-13-trans-dienoic acid (V). The reduction of (V) with H2 over Pd/C in methanol affords the 13-trans-prostenoic acid (VI), which is methylated with CH2N2 in ether yielding the methyl ester (VII). The reduction of (VII) with diisobutyl aluminum hydride in toluene affords the corresponding aldehyde (VIII), which by a Wittig reaction with triethyl phosphonoacetate (IX) by means of NaH in THF is converted into 9alpha-hydroxy-11alpha,15alpha-bis(tetrahydropyranyloxy)-16,16-dimethylprosta-2-trans-dienoic acid ethyl ester (X). The hydrolysis of the ester (X) with KOH in ethanol-water gives the corresponding acid (XI), which is oxidized with CrO3, MnSO4 and H2SO4 in ether - water yielding the protected ketoacid (XII). The hydrolysis of (XII) with acetic acid-water at 80 C gives 9-oxo-11alpha,15alpha-dihydroxy-16,16-dimethyl-prosta-2-trans-13-trans-dienoic acid (16,16-dimethyl-DELTA2-trans-PGE1) (XIII), which is finally methylated with CH2N2 in ether

合成路线2

The esterification of bromoacetic acid (I) with benzyl alcohol (II) gives the corresponding ester (III), which by reaction with triphenylphosphine (IV) in hot toluene yields the phosphonium bromide (V). The reaction of (V) with NaOH in water-dichloromethane affords benzyl(triphenylphosphoranylidene) acetate (VI), which is submitted to a Wittig condensation with 5-(hydroxymethyl)-2-pyrrolidone (VII) in the presence of Dess-Martin periodinane (DMPI) giving benzyl 3-(5-oxo-2-pyrrolidinyl)-2(E) propenoate (VIII). The acylation of (VIII) with 4-methoxybenzoyl chloride (IX) by means of triethylamine in hot toluene yields the corresponding amide (X), which is finally hydrogenated and deprotected with H2 over Pd/C in THF.

合成路线3

The treatment with NaHCO3 of the corresponding mixture of the 6(R)- and 6(S)-SO2-aldehydic adducts (VIII) gives a mixture of the 20(R) and 20(S) epimeric aldehydes (IX). The Wittig condensation of the aldehyde mixture (IX) with cyclopropylcarbonylmethylenetriphenylphosphorane (X) [prepared from acetylcyclopropane (XI) by bromination to bromoacetylcyclopropane (XII), reaction with triphenylphosphine (XIII) to the phosphonium salt (XIV) and treatment with NaOH] in DMSO at 105 C, followed by chromatographic separation yields the epimeric 20(R)-enone (XV). The reduction of (XV) with NaBH4 and CeCl3 in THF-methanol, followed by chromatographic purification affords the epimeric 3'(R)-allylic alcohol (XVI), which is isomerized by irradiation with UV-light from a TQ 718Z2 Hanau lamp in toluene in the presence of anthracene to give the corresponding 5(Z)-derivative (XVII). Finally, this compound is deprotected by a treatment with tetrabutylammonium fluoride in THF at 60 C.

合成路线4

The condensation of 4-methoxypyridine-3-carbaldehyde (I) with 2-azidoacetic acid ethyl ester (II) by means of NaOMe in ethanol gives 2-azido-3-(4-methoxypyridin-3-yl)acrylic acid ethyl ester (III), which is cyclized in refluxing o-xylene to yield the pyrrolopyridine (IV). The reaction of the NH group of (IV) with Sem-Cl and NaH in DMF affords the N-protected compound (V), whose ester group is reduced with LiAlH4 in refluxing THF to provide the carbinol (VI). The oxidation of (VI) with MnO2 in dichloromethane gives the corresponding carbaldehyde (VII), which is condensed with 2-azidoacetic acid ethyl ester (II) as before to yield the azido acrylic ester (VIII). The condensation of (VIII) with triphenylphosphine (IX) in dichloromethane affords the iminophosphorane (X), which is N-deprotected by means of TBAF in THF to provide the deprotected iminophosphorane (XI). The cyclization of (XI) with alpha-methylbenzyl isocyanate (XII) in THF gives the tricyclic pyrimidopyrrolopyridine (XIII), which is brominated with Br2 in pyridine to yield intermediate (XIV). The reaction of (XIV) with 1-ethoxyvinyl trimethyl tin (XV) by means of PdCl2(PPh3)2 in DMF affords the acetyl derivative (XVI), which is condensed with dimethylformamide di-tert-butyl acetal (XVII) in hot DMF to provide the dimethyl enaminone (XVIII). The cyclization of (XVIII) with guanidine (XIX) by means of K2CO3 in refluxing 2-methoxyethanol gives the 2-aminopyrimidine derivative (XX), with simultaneous hydrolysis of the ester group. The decarboxylation of (XX), with simultaneous demethylation, by heating at 260 C in diphenyl ether yields the N-protected precursor (XXI), which is finally treated with triflic acid to afford the target variolin B.

合成路线5