Manufacturing Process
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone is added to a solution of PGF2a
[(5Z,11α,13E)-11,15-dihydroxy-9-oxoprosta-5,13-dien-1-oic acid or
Prostaglandin E2] in dioxane. The mixture is stirred 24 h at 50°C under
nitrogen, and then is cooled to 20°C and filtered. The filtered solids are
washed with dichloromethane. Evaporation of the combined filtrate and
washings at reduced pressure gives a residue which is chromatographed on
silica gel (Silicar CC-4; Malincrodt), eluting with 50% ethyl acetate in
Skellysolve B (a mixture of isomeric hexanes). Evaporation of the eluates
gives 15-oxo-PGF2a.
A mixture of hexamethyldisilazane and tri-methylchlorosilane is added to a
solution of 15-oxo-PGF2a in tetrahydrofuran. This mixture is stirred 16 h at
25°C under nitrogen, and is then filtered. The filtrate is evaporated under
reduced pressure. Xylene is added to the residue and the mixture is
evaporated at 60°C under reduced pressure. This addition of xylene and
evaporation is repeated twice. The resulting residue is the tris-(trimethylsilyl)
derivative of 15-oxo-PGF2a.
A 3 M diethyl ether solution of methylmagnesium bromide is added dropwise
to a stirred solution of the tris-(trimethylsilyl) derivative of 15-oxo-PGF2a in
diethyl ether at 25°C.
The mixture is stirred 30 min at 25°C, after which an additional the
methylmagnesium bromide solution is added and stirring is continued an
additional 30 min. The resulting reaction mixture is poured into saturated
aqueous ammonium chloride solution at 0°C. After stirring several minutes,
the mixture is extracted repeatedly with diethyl ether. The combined diethyl
ether extracts are washed with saturated aqueous sodium chloride solution
and then dried with anhydrous sodium sulfate. Evaporation of the diethyl
ether gives a yellow oil which is dissolved in ethanol. That solution is diluted
with water, and the mixture is stirred 4 h at 25°C. The ethanol in the resulting
solution is evaporated at reduced pressure, and the aqueous residue is
saturated with sodium chloride and then extracted with ethyl acetate.
Solution, dried with anhydrous sodium sulfate, and evaporated under reduced
pressure to give a mixture of 15-methyl-PGF2a and 15-methyl-15(R)-PGF2a.
The 520.0 mg mixture of 15-methyl-PGF2a and 15-methyl-15(R)-PGF2a is
dissolved in diethyl ether and cooled to 0°C. Excess diazomethane dissolved in
diethyl ether is then added, and the mixture is maintained 5 min at 0°C and
then 5 min at 25°C. The solution is evaporated in a stream of nitrogen, and
the residue is chromatographed on 500.0 g of neutral silica (Merck), eluting
successively with 20%, 40%, and of 50% ethyl acetate in Skellysolve B. The
corresponding eluates emerging from the column are discarded. Elution is
continued successively with gradients of 4 L of 50% and 4 L of 60% ethyl
acetate in Skellysolve B, and 5 L of 60% and 5 L of 75% ethyl acetate in
Skellysolve B, and then with 4 L of 75% ethyl acetate in Skellysolve B,
collecting the corresponding eluates in 500 ml fractions. Elution is further
continued successively with 5 L of 75% ethyl acetate in Skellysolve B and with
6 L of 100% ethyl acetate, collecting the corresponding eluates in 200 ml
fractions. Eluate fractions 29-35 are combined and evaporated to give 109.0
mg of 15-methyl-15(R)-PGF2a methyl ester.
Aqueous potassium hydroxide solution is added to a solution of 15-methyl-
15(R)-PGF2a methyl ester in a mixture of methanol and of water under
nitrogen. The resulting solution is stirred 2 h at 25°C, and is then poured into
several volumes of water. The aqueous mixture is extracted with ethyl
acetate, acidified with 3 N hydrochloric acid, saturated with sodium chloride,
and then extracted repeatedly with ethyl acetate. The latter ethyl acetate
extracts are combined, washed successively with water and saturated aqueous
sodium chloride solution, dried with anhydrous sodium sulfate, and evaporated
under reduced pressure. The crystalline residue is recrystallized from a
mixture of ethyl acetate and Skellysolve B to give 15-methyl-15(R)-PGF2a.
