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

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is an importantmetabolite of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Using the chiral derivatizing agent, (R)-(+)-alpha-methylbenzyl isocyanate [(R)-(+)-MBIC], previous work has shownthat the enantiomeric ratio of metabolically formed NNAL and itsglucuronide derivative may be species dependent. However, the absoluteconfiguration of such NNAL has not been previously reported. Syntheticallyprepared racemic NNAL was converted to diastereomeric esters by reactionwith (R)-(+)- and (S)-(-)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetic acid (MTPA) chloride (Mosher's reagent) andthe products were characterized by 1H-NMR. Based on chemical shift data,the absolute configuration of NNAL in each diastereomeric ester wasassigned. Hydrolysis of (R)-NNAL-(R)-MTPA gave (R)-NNAL. This was convertedto the corresponding carbamate by reaction with (R)-(+)-alpha- MBIC and theabsolute configurations of the diastereomeric carbamates formed by reactionof (R)- and (S)-NNAL with (R)-(+)-MBIC were thereby assigned. Conversion ofmetabolically produced NNAL to the same carbamates allowed us to assign theNNAL formed from NNK by rat liver microsomes as (R)-NNAL. The major andminor NNAL-glucuronide diastereomers found in the urine of patas monkeysand humans exposed to NNK were similarly assigned; they were formed from(R)-NNAL and (S)- NNAL, respectively.