Absolute configuration of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol formed metabolically from 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone

S. Hecht
1997 Carcinogenesis  
believed to be detoxification products of NNK, have been 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is identified in the urine of NNK treated animals as well as in an important metabolite of the tobacco-specific nitrosamine people exposed to NNK (6-11). NNAL can also be reconverted 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). to NNK metabolically, although the equilibrium favors Using the chiral derivatizing agent, (R)-(⍣)-α-methyl-NNAL (12). benzyl isocyanate [(R)-(⍣)-MBIC],
more » ... previous work has Although NNAL plays a central role in carcinogenesis by NNK, shown that the enantiomeric ratio of metabolically formed the absolute configuration of metabolically formed NNAL has NNAL and its glucuronide derivative may be species not been reported. In this study, we employed α-methoxy-αdependent. However, the absolute configuration of such (trifluoromethyl)phenylacetic acid (MTPA, 'Mosher's reagent') NNAL has not been previously reported. Synthetically to determine the absolute configuration of NNAL (13,14). This prepared racemic NNAL was converted to diastereomeric information was used to assign the stereochemistry of NNAL esters by reaction with (R)-(⍣)-and (S)-(-)-α-methoxy-α- produced by rat liver microsomes, as well as the stereochemistry (trifluoromethyl)phenylacetic acid (MTPA) chloride of NNAL-Gluc found in rat, monkey and human urine after (Mosher's reagent) and the products were characterized exposure to NNK. by 1 H-NMR. Based on chemical shift data, the absolute NNK and racemic NNAL were synthesized (15-17). (R)configuration of NNAL in each diastereomeric ester was (ϩ)-MTPA, (S)-(-)-MTPA, (R)-(ϩ)-α-methylbenzyl isocyanassigned. Hydrolysis of (R)-NNAL-(R)-MTPA gave (R)ate [(R)-(ϩ)-MBIC], and (S)-( -)-MBIC were obtained from NNAL. This was converted to the corresponding carbamate the Aldrich Chemical Co. (Milwaukee, WI). 1 H-NMR spectra by reaction with (R)-(⍣)-α-MBIC and the absolute config- were obtained on a Bruker Model AM 360 WB spectrometer urations of the diastereomeric carbamates formed by reacand MS on a Finnigan-MAT TSQ 700 instrument. tion of (R)-and (S)-NNAL with (R)-(⍣)-MBIC were thereby The MTPA esters of NNAL were prepared by reacting 0.075 assigned. Conversion of metabolically produced NNAL to mmol of racemic NNAL with 0.4 mmol of either (R)-or the same carbamates allowed us to assign the NNAL formed (S)-MTPA chloride in 2 ml CH 2 Cl 2 containing 2.4 mmol from NNK by rat liver microsomes as (R)-NNAL. The triethylamine. The reaction mixture was stirred at room tempermajor and minor NNAL-glucuronide diastereomers found ature overnight, and 0.4 mmol of dimethylaminopropylamine in the urine of patas monkeys and humans exposed to was added. The crude product was purified by column chroma-NNK were similarly assigned; they were formed from (R)tography on silica gel followed by HPLC collection (Rainin NNAL and (S)-NNAL, respectively. Microsorb-MV C18 column, 5 µm, Solvent A 20 mM sodium phosphate, pH 7, Solvent B methanol, program 0-100%
doi:10.1093/carcin/18.9.1851 pmid:9328186 fatcat:mpeoojoyercllajzmb7bsqr7xe