Protonation of phosphoramide mustard and other phosphoramides.
The chemistry of the bifunctional alkylating agent phosphoramide mustard and model phosphoramides was probed by multinuclear NMR spectroscopy as a function of pH. Between pH 1 and 11, both the 31P and 15N resonances for phosphoramide mustard displayed a single monobasic titration curve with a pKa of 4.9. The protonation below pH 4.9 correlates with the loss in reactivity of the mustard. The 17O NMR spectrum of 17O-enriched phosphoramide mustard shows little change with pH. The data on the mustard was compared to 15N and 31P NMR data on 15N-enriched phosphoramidic acid, phosphorodiamidic acid, and phosphoric triamide. Contrary to the conclusions of previous studies, our combined 31P, 15N, and 17O NMR results are more consistent with N-protonation of phosphoramide mustard rather than an O-protonation. Theoretical calculations on the phosphoramidic acid, phosphorodiamidic acid, and phosphoric triamide show O-protonation to be more stable in the gas phase. For the latter two compounds, the calculations suggest that N-protonation may be the most stable protonated form in the aqueous phase. These findings influence our understanding of the structure-activity relationships of phosphoramide mustards.
Gamcsik
M P
MP
Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Ludeman
S M
SM
Shulman-Roskes
E M
EM
McLennan
I J
IJ
Colvin
M E
ME
Colvin
O M
OM
D000577:Amides / Q000737:chemistry*; D000970:Antineoplastic Agents / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004355:Drug Stability; D005740:Gases; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010752:Phosphoramide Mustards / Q000737:chemistry*; D063088:Phosphoramides; D010756:Phosphoric Acids / Q000737:chemistry*; D011522:Protons; D013816:Thermodynamics
D000577:Amides; D000970:Antineoplastic Agents; D005740:Gases; D010752:Phosphoramide Mustards; D063088:Phosphoramides; D010756:Phosphoric Acids; D011522:Protons; C030090:phosphoramide mustard; C005438:phosphoramide; C011067:phosphoramidic acid