Ebalzotan

A stereoselective synthesis of bicyclic primary or secondary amines, based on tetralin or chroman structural moieties, is reported. These amines are precursors of important active pharmaceutical ingredients such as rotigotine (Neupro), robalzotan, and ebalzotan. The key step is based on a multienzymatic reduction of an α,β-unsaturated aldehyde or ketone to give the saturated primary or secondary alcohol, in a high yield and with a high ee. The catalytic system consists of the combination of an ene-reductase (ER; i.e., OYE2 or OYE3 belonging to the Old Yellow Enzyme family) with an alcohol dehydrogenase (ADH), applying the in situ substrate feeding product removal technology. By this system the formation of the allylic alcohol side product and the racemization of the chirally unstable α-substituted aldehyde intermediate are minimized. The primary alcohols were elaborated via a Curtius rearrangement. The combination of OYE2 with a Prelog or an anti-Prelog ADH allowed the preparation of the secondary alcohols with ee > 99% and de > 87%. The absolute configuration of the primary amines was unambiguously assigned by comparison with authentic samples. The stereochemistry of secondary alcohols was assigned by X-ray crystal structure and NMR analysis of Mosher esters.

The pharmacological properties of the 5-hydroxytryptamine (HT)(1A) receptor agonist (R)-3,4-dihydro-N-isopropyl-3-(N-isopropyl-N-propylamino)-2H-1-benzopyran-5-carboxamide (NAE-086) were examined with in vitro and in vivo techniques. Receptor binding studies demonstrated that NAE-086 was a high-affinity and selective 5-HT(1A) receptor ligand with a K(i) value of 4.5 nM in membranes from rat hippocampus. Of 32 other receptors examined NAE-086 had a modest affinity only for the 5-HT(7) receptor (K(i) = 240 nM). NAE-086 inhibited VIP-stimulated adenylyl cyclase activity in GH(4)ZD10 cells with 79% of the efficacy of 5-HT. This inhibition was blocked by the 5-HT(1A) receptor (and beta-adrenoceptor) antagonist (-)alprenolol. A minor metabolite of NAE-086 in rats, (R)-3,4-dihydro-3-(N-isopropyl-N-propylamino)-2H-1-benzopyran-5-carboxamide had a similar receptor profile but had 17 times higher affinity for the 5-HT(1A) receptor (K(i) = 0.26 nM). In vivo, NAE-086 induced all the typical effects of a 5-HT(1A) receptor agonist in rats: it decreased 5-HT synthesis (5-HTP accumulation) and 5-HT turnover (measured as the ratio of 5-hydroxyindoleacetic acid/5-HT), increased corticosterone secretion, induced the 5-HT(1A) syndrome (flat body posture and forepaw treading), inhibited the cage-leaving response, and caused hypothermia. All the responses mediated by postsynaptic 5-HT(1A) receptors were attenuated after single or repeated treatment of the rats with NAE-086. Simultaneously with the development of the tolerance to 5-HT(1A) receptor-mediated responses, 5-HT(2A) receptor-mediated responses were enhanced, as judged from the increased number of spontaneous and/or agonist [1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane]-induced wet-dog shake responses. The significance of this behavioral effect in relation to clinical observations is discussed.