Detection of 3,3’-Spirobiphthalide from the Oxidation of Amitriptyline
Sir: In a recent publication Wallace et al. ( I ) described a procedure for the determination of the drug amitriptyline in body fluids. Their procedure involved gas-liquid chromatography with electron capture detection (GLC-ECD) of the anthraquinone formed after oxidation of amitriptyline with ceric sulfate-sulfuric acid. When we followed this (substituting 1-chloroanthraquinone for ethylanthraquinone as internal standard), we observed another compound, apart from the expected anthraquinone (Figure 1A). This compound was extracted into heptane from the acidic solution, but was removed if the heptane phase was washed with 0.1 M sodium hydroxide as in the procedure of Hartvig et al. (2). U’hen 0.05 M potassium dichromate (in 3 M sulfuric acid) was used as oxidizing agent, the unknown compound was the only product detected by GLC-ECD (Figure IR). Further investigations using GLC-FID indicated that the major product of the dichromate oxidation was dibenzosuberone (5H-dibenzo-10,ll-dihydro[a,d]cyclohepten-5-one), which was not detected under our GLC-ECD conditions, and that this compound was itself oxidized to the unknown in low yield. A large-scale dichromate oxidation of dibenzosuberone yielded a few milligrams of pure compound (mp 209-212 “C), identical on GLC with the unknown. The elemental analysis was consistent with a molecular formula of CI5H8O4.The mass 252 (l),209 (X), spectrum contained peaks at m / e : 253 (170), 208 (971,207 (E),181 (151, 180 (loo), 179 (61, 153 ( l o ) , 152 (79), 151 (25), 150 (lo), 126 (8), 104 (21), 76 ( 5 2 ) . The IR spectrum contained a strong absorption a t 1800 cm From these data, the unknown was identified as 3,3’spirobiphthalide (1,1’(3H,3’H)spirobi[isobenzofuran]-3,3’dione) (I).
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Figure 1. GLC-ECD trace ( 3 % OV-17) following injection of 1 / 2 0 of heptane extract from oxidation of 100 ng of amitriptyline HCI. ( A ) Ceric sulfate oxidation, (€3) dichromate oxidation. (1) Anthraquinone: (2) 1-chloroanthraquinone (1 ng); (3) unknown
I This compound has previously been isolated from oxidations of compounds belonging to the dibenzo[a,d]cycloheptene system (3-6), of which amitriptyline is a member. The electron capture response of 3,3’-spirobiphthalide was approximately 8.5 times that of anthraquinone, and its minimum detectable quantity was in the order of 2 pg. Dichromate oxidations of amitriptyline gave this compound in yields which varied from 22% (2 ng amitriptyline oxidized) to 970 (200 ng oxidized). Therefore, although the electron capture r~esponseto the 3,3’-spirobiphthalide provided a sensitive detection of the parent drug, an accurate quantitation was not possible by a dichromate oxidation.
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ANALYTICAL CHEMISTRY, VOL. 49, NO. 12, OCTOBER 1977
LITERATURE CITED (1) J. E. Wallace, H. E. Hamilton, L. K . Goggin, and K. Blum. Anal. Chem , 47, 1516 (1975). (2) P. Hamig, S. Strandberg, and B. Naslund, J . Chromatogr., 118, 65 (1976). (3) W. Treibs and H. J. Klinkhammer, Chem. Ber.. 83, 367 (1950). (4) G. Berti. Gazz. Chim. [fa/, 87, 293 (1957). ( 5 ) J. Cristol and K. Ruta, J , A m . Chem. SOC.,82, 6155 (19601. (6) J. Rigaudy and L. Nedelec. Bull. SOC. Chim. F r . , 400 (1960).
A. W. Missen* H. M.S t o n e Chemistry Division, DSIR Private Bag Petone, New Zealand
RECEIVED for review April 20, 1977. Accepted May 27, 1977.
