Preparative HPLC separation of bambuterol enantiomers and stereoselective inhibition of human cholinesterases

Abstract

We separated and characterized the enantiomers of bambuterol (5-[-(tert-butylamino)-1-hydroxyethyl]-m-phenylene-bis(dimethylcarbamate) hydrochloride), which is used in racemic form as a prodrug of terbutaline, a beta(2)-adrenoceptor agonist. The enantioseparation was attempted on several chiral HPLC columns, and the most effective separation was achieved on the amylose-based Chiralpak AD column. Since in vivo conversion of bambuterol into terbutaline involves hydrolysis by butyrylcholinesterase (EC 3.1.1.8), we studied the reaction of enantiomers with eight human BChE variants. Both enantiomers inhibited all studied BChE variants; however, the rate of inhibition with the (R)-enantiomer was about five times faster than with the (S)-enantiomer. (R)-bambuterol inhibition rate constants for homozygous usual (UU), fluoride-resistant (FF) or atypical (AA) variant ranged from 6.4 to 0.11 min(-1)microM(-1). The inhibition rates for heterozygotes were between the respective constants for the corresponding homozygotes.

Stereoselective Inhibition of Human Butyrylcholinesterase by the Enantiomers of Bambuterol and Their Intermediates

“…The enantioselective time-and concentration-dependent inhibition mechanism obtained when BMB enantiomers were used as inhibitors is in agreement with previously reported findings and confirms the hydrolysis model (Fig. 1) previously proposed (Kovarik and Simeon-Rudolf, 2004;Gazi c et al, 2006). In fact, according to this model, the interaction between BMB and BChE results in a virtually irreversible complex formation, and this is consistent with the linear correlation between the pseudo-first-order rate constant (k obs ) and BMB concentration (Fig.…”

“…Since the relationship was linear for all the molecules under investigation, the data were analyzed as for a simple irreversible inhibition, and the second-order inhibition (carbamylation) rate constant (k I ) was calculated from eq. 3 (Marangoni, 2003;Gazi c et al, 2006):…”

Highly enantioselective synthesis, crystal structure, and circular dichroism spectroscopy of (R)‐bambuterol hydrochloride

“…It is also reported that (R)-enantiomer of bambuterol was about five times more potent for the inhibition of BuChE than (S)-enantiomer. 10 Furthermore, in recent years, a suspicion has been raised that the (S)-enantiomer of b 2 -adrenoceptor agonists may cause airway hyper-reactivity and even contribute to an increase in asthma death. 11 The present study investigated the asymmetric synthesis of (R)-bambuterol or (S)-bambuterol that was achieved by the reagent-controlled reduction of the corresponding aralkyl ketone with (2)-DIP-chloride TM or (1)-DIP-chloride TM .…”

Cholinesterases: Structure, Role, and Inhibition

“…AChE je tako stereoselektivna prema karbamatima (-)-fizostigminu, (-)-fizoveninu, (-)-kimserinu i (R)-bambuterolu, dok su AChE i BChE pokazale veći afi nitet prema (R)-etopropazinu, lijeku koji se, u obliku racemata, rabi kao neuroleptički lijek u tretmanu Parkinsonove bolesti (93)(94)(95)(96)(97). Karboksilni esteri, esteri karbaminske kiseline i trifl uoracetofenoni planarne su molekule kod kojih su skupine vezane direktno na elektrofi lni ugljik pod kutovima od 120º čineći tako trigonalnu geometriju.…”