2,4-Dioxa-7-aza-, 2,4-Dioxa-8-aza-, and 2,4-Dioxa-9-aza-3-phosphadecalins as Rigid Acetylcholine Mimetics: Syntheses and Characterization

Design, Synthesis, and Monoamine Oxidase Inhibitory Activity of (+)-Cinchonaminone and Its Simplified Derivatives

The absolute structure of an indole alkaloid (+)-cinchonaminone by total synthesis of both (+)-cinchonaminone and its enantiomer was determined. The main focus of the study was the enantioselective synthesis of both enantiomers of a chiral cis-3,4-disubstituted piperidine. We also evaluated monoamine oxidase (MAO) inhibitory activities of these enantiomers. Furthermore, its structurally simplified derivatives were synthesized that did not have any chiral center. Two of these derivatives showed stronger MAO inhibitory activities than that of (+)-cinchonaminone.

Radiolabelling of 1,4-disubstituted 3-[18F]fluoropiperidines and its application to new radiotracers for NR2B NMDA receptor visualization

In order to develop a novel and useful building block for the development of radiotracers for positron emission tomography (PET), we studied the radiolabelling of 1,4-disubstituted 3-[(18)F]fluoropiperidines. Indeed, 3-fluoropiperidine became a useful building block in medicinal chemistry for the pharmacomodulation of piperidine-containing compounds. The radiofluorination was studied on substituted piperidines with electron-donating and electron-withdrawing N-substituents. In the instance of electron-donating N-substituents such as benzyl or butyl, configuration retention and satisfactory fluoride-18 incorporation yields up to 80% were observed. In the case of electron-withdrawing N-substituents leading to carbamate or amide functions, the incorporation yields depend on the 4-susbtitutent (2 to 63%). The radiolabelling of this building block was applied to the automated radiosynthesis of NR2B NMDA receptor antagonists and effected by a commercially available radiochemistry module. The in vivo evaluation of three radiotracers demonstrated minimal brain uptakes incompatible with the imaging of NR2B NMDA receptors in the living brain. Nevertheless, moderate radiometabolism was observed and, in particular, no radiodefluorination was observed which demonstrates the stability of the 3-position of the fluorine-18 atom. In conclusion, the 1,4-disubstituted 3-[(18)F]fluoropiperidine moiety could be of value in the development of other radiotracers for PET even if the evaluation of the NR2B NMDA receptor antagonists failed to demonstrate satisfactory properties for PET imaging of this receptor.

Synthesis and in vitro characterization of trans- and cis-[(18)F]-4-methylbenzyl 4-[(pyrimidin-2-ylamino)methyl]-3-fluoropiperidine-1-carboxylates as new potential PET radiotracer candidates for the NR2B subtype N-methyl-D-aspartate receptor

Diastereoisomeric compounds [(18)F]cis- and [(18)F]trans-4-methylbenzyl 4-[(pyrimidin-2-ylamino)methyl]-3-fluoro-piperidine-1-carboxylates were successfully synthesized as new subtype-selective PET radiotracers for imaging the NR2B subunit containing NMDA receptors. Rat brain section autoradiographies demonstrated a high specific binding in NR2B/NMDA receptor rich regions for both radioligands. The measured logD(7.4) values as well as B(max)/K(d) ratios indicated that both radiotracers possess the adequate properties required for PET radiotracers.

(40) The stereochemistry of the inhibition of acetylcholinesterase with acetylcholine-mimetic 7-aza-2,4-dioxaphosphadecalins

The irreversible inhibition of acetylcholinesterase with the decalin-type cis- and trans-3-fluoro-2,4-dioxa-7-aza-3-phosphadecalins was investigated by 31P-NMR spectroscopy. The stereochemical outcome (inversion or retention at the P-atom) is dependent on the structure of the inhibitors.

(39) Decalin-type acetylcholine-mimetic organophosphates as inhibitors of acetylcholinesterase

The novel decalin-type N,O,P-heterocycles, P(3)-axially and P(3)-equatorially substituted cis- and trans-configurated 3-fluoro-2,4-dioxa-7-aza-, 2,4-dioxa-8-aza-, and 2,4-dioxa-9-aza-3-phosphabicyclo[4.4.0]decane 3-oxides, are configuratively fixed and conformationally constrained phosphorus analogues of acetylcholine. The compounds are suitable probes for the investigation of molecular interactions with acetylcholinesterase.