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SYNTHESIS OF ESTROGEN METHYL ETHERS BY EXTRACTIVE ALKYLATION J.D. Daley+, J.M. Rosenfeld* and E.V. YoungLai

+*

Departments of +Obstetrics and Gynecology and of Pathology, Program in Reproductive Biology, McMaster University Medical Centre, Hamilton, Ontario, Canada LSS 4J9.

Received:l2/5/75

ABSTRACT

A rapid method for the quantitative preparation of a number of estrogen methyl ethers is described. Estrogen in aqueous base is extracted as an ion pair with the tetrahexylammonium ion into methylene chloride where irreversible alkylation (extractive alkylation) by methyl iodide occurs. Gas chromatography (GC) - mass spectrometry (MS) provided the basis for identification of the methylated products. Estrone (1) and estradiol were easily 3-O-methylated whereas estriol gave a dimethylated product. Further experiments suggested that dimethylation of 2-hydroxyestrone in reasonable yield was possible. INTRODUCTION The Brown method

(2) for the preparation of estrogen

methyl ethers using dimethyl sulphate is widely used for the purification and characterization of natural and synthetic estrogens

(3,4).

Other estrogen methylation procedures have

been reported but these require vacuum sublimation

(5) or

extended reaction times (6) and are therefore unsuitable for work requiring the repetitive analysis of many samples. Here we report a rapid and convenient method for the preparation of estrogen methyl ethers by an ion pair phase transfer alkylation reaction otherwise known as "extractive alkylation"

(7).

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MATERIALS AND METHODS Chemicals: Estrone (El), estradiol-178 (Ez-176), estradiol17a(Ez-17a), estriol (Es) and 3-methoxyestriol (E30Me) were purchased from Steraloids. 3-Methoxyestrone (ElOMe) and 3methoxyestradiol-178 (EzOMe-176) were from Sigma. Purity and identity were established by paper chromatography (PC), thin layer chromatography (TLC), gas chromatography (GC) and mass spectrometry (MS). 2-Hydroxyestrone (2-OHEl) , 2-methoxyestrone (2-OMeEl), 2-hydroxy-3-methoxyestrone (2-OHElOMe) and 2,3-dimethoxyestrone (2,3-diOMeE1) were generously donated by Dr. K.I.H. Williams, Worcester Foundation. El [6,7-3~] (40 Ci/mM), E2-178 [6,7-3~1 (48 Ci/mM) and EB [6, 7-3H] (52 Ci/mM) were purchased from New England Nuclear and were at least 98% pure. All solvents were reagent grade and redistilled before use except for diethyl ether (BDH) which was analytical reagent grade and used directly. Methyl iodide (Fisher) was fractionally redistilled or used from freshly opened bottles. Tetrahexylammonium iodide (THAI) was from Eastman Chemicals and powdered silver oxide from BDH. Paper Chromatography: Chromatography on Whatman #l paper in the solvent system heptane:methanol:water (5:4:1) was according to Bush (8). Steroids were visually located by spraying the chromatogram with 3.5% phosphomolybdic acid (Merck) followed by brief heating at 1lOoC. Thin Layer Chromatography: Solvent systems used are listed in Table 1. TLC in systems A and B was on 20x20 cm plastic TABLE 1. System

Composition of Solvent Systems Composition in parts by volume

A

benzene:ethyl acetate

(2:l)

B

benzene:ethyl acetate

(13:l)

C

cyclohexane:ethyl

D

ethyl acetate:n-hexane:ethanol

E

chloroform:ethanol

acetate:ethanol

(9:9:2)

(16:3:1)

(9:l)

sheets precoated with 0.25 mm silica gel F-254 (Merck) or with 0.25 mm silica gel G/W 254 (Macherey-Nagel) for solvent systems C-E.

Gas Chromatography: For GC a Varian, Series 2100 gas chromatosraph with a flame ionization detector and a 6 ft x 4 in (I.D.)-glass column packed with 3% OV-17 on Chromosorb W-HP 80/100 mesh (Chromatographic Specialties) was used with the operating parameters: injection port temp 305OC; detector 305OC; column 270°C; N2 carrier gas flow 40 ml/min. Relative retention times were measured with testosterone acetate as internal standard. Sample injection was 0.5-1.0 pg in 1 ~1 methanol. The coefficient of variation for retention times on repeated sample runs was

Synthesis of estrogen methyl ethers by extractive alkylation.

A rapid method for the quantitative preparation of a number of estrogen methyl ethers is described. Estrogen in aqueous base is extracted as an ion pa...
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