Chemical stability and fate of the cytostatic drug ifosfamide and its N-dechloroethylated metabolites in acidic aqueous solutions.
31P NMR spectroscopy was used to study the products of the decomposition of the antitumor drug ifosfamide (IF, 1d) and its N-dechloroethylated metabolites, namely, 2,3-didechloroethylIF (1a) and 2- (1b) and 3-dechloroethylIF (1c), in buffered solutions at acidic pH. The first stage of acid hydrolysis of these four oxazaphosphorines is a P-N bond cleavage of the six-membered ring leading to the phosphoramidic acid monoesters (2a-d) of type R'HN(CH(2))(3)OP(O)(OH)NHR, with R and/or R' = H or (CH(2))(2)Cl. The electron-withdrawing chloroethyl group at the endocyclic and/or exocyclic nitrogens counteracts the endocyclic P-N bond hydrolysis. This effect is even more marked when the N-chloroethyl group is in the exocyclic position since the order of stability is 1d > 1c > 1b > 1a. In the second stage of hydrolysis, the remaining P-N bond is cleaved together with an intramolecular attack at the phosphorus atom by the non-P-linked nitrogen of the compounds 2a-d. This leads to the formation of a 2-hydroxyoxazaphosphorine ring with R = H (3a coming from compounds 2a,c) or (CH(2))(2)Cl (3b coming from compounds 2b,d) and to the release of ammonia or chloroethylamine. The third step is the P-N ring opening of the oxazaphosphorines 3a,b leading to the phosphoric acid monoesters, H(2)N(CH(2))(3)OP(O)(OH)(2) (4a) and Cl(CH(2))(2)HN(CH(2))(3)OP(O)(OH)(2) (4b-1), respectively. For the latter compound, the chloroethyl group is partially (at pH 5.5) or totally (at pH 7.0) cyclized into aziridine (4b-2), which is then progressively hydrolyzed into an N-hydroxyethyl group (4b-3). Compounds 3a,b are transient intermediates, which in strongly acidic medium are not observed with (31)P NMR. In this case, cleavage of the P-N bond of the type 2 phosphoramidic acid monoesters leads directly to the type 4 phosphoric acid monoesters. The phosphate anion, derived from P-O bond cleavage of these latter compounds, is only observed at low levels after a long period of hydrolysis. Compounds 1a-c and some of their hydrolytic degradation products (4b-1, 4b-2, diphosphoric diester [Cl(CH(2))(2)NH(CH(2))(3)OP(O)(OH)](2)O (5), and chloroethylamine) did not exhibit, as expected, any antitumor efficacy in vivo against P388 leukemia. (31)P NMR determination of the N-dechloroethylated metabolites of IF or its structural isomer, cyclophosphamide (CP), and their degradation compounds could provide an indirect and accurate estimation of chloroacetaldehyde amounts formed from CP or IF.
Biomedical NMR Group, IMRCP Laboratory, Université Paul Sabatier, 118, route de Narbonne, 31062 Toulouse, France.
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V
Gilard
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Martino
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Malet-Martino
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Niemeyer
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J
Pohl
D000577:Amides / Q000737:chemistry; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology / Q000633:toxicity / Q000652:urine; D004355:Drug Stability; D005260:Female; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007069:Ifosfamide / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000494:pharmacology / Q000633:toxicity / Q000652:urine; D007700:Kinetics; D007928:Lethal Dose 50; D007941:Leukemia P388 / Q000188:drug therapy; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051379:Mice; D009368:Neoplasm Transplantation; D010752:Phosphoramide Mustards / Q000737:chemistry* / Q000494:pharmacology / Q000633:toxicity; D010756:Phosphoric Acids / Q000737:chemistry; D010759:Phosphorus Isotopes; D051381:Rats; D014407:Tumor Cells, Cultured; D014867:Water
C120310:2,3-didechloroethylifosfamide; D000577:Amides; D000970:Antineoplastic Agents; D010752:Phosphoramide Mustards; D010756:Phosphoric Acids; D010759:Phosphorus Isotopes; D014867:Water; C011067:phosphoramidic acid; C038007:dechloroethylifosfamide; D007069:Ifosfamide