Catalytic Transfer Hydrogenolysis ofN-Benzyl Protecting Groups

Five Step Total Synthesis of Lythranidine

A concise synthesis of the alkaloid lythranidine is reported. The strategy exploits the target's local C₂ symmetry by adopting a two directional synthetic approach, first in an acyclic environment, then in a cyclic system and finally in a bridged macrocyclic domain. The latter phase of the synthesis, which installs all four stereocenters, involves a thermodynamically controlled, twofold intermolecular/transannular aza-Michael addition and a twofold hydride reduction. The synthesis is one third of the length of the most step-economic previous approach, providing access to gram quantities of the natural product. The broad-spectrum nature of the synthesis is demonstrated through the preparation of three diastereomeric analogues of the natural product.

A synthetic study toward the core structure of (-)-apicularen A

A concise synthetic strategy towards the core structure of (-)-apicularen A has been described in an 11-step synthetic sequence from a known intermediate. The key steps include tandem isomerization followed by C-O and C-C bond-forming reactions and iodocyclization strategies for the synthesis of a bicyclic ether embedded in the macrolactone ring. The applied reagent-controlled Keck-Maruoka allylation, Lin Pu alkynylation and Ricket-Diels-Alder reactions were used to simplify the synthetic sequence of related natural products. An intramolecular Yamaguchi lactonization constructed the macrolactone core, while the attempt to install the C11 hydroxyl chiral centre either under catalytic hydrogenation conditions or oxidative conditions was not successful.

Synthetic applications of hypophosphite derivatives in reduction

The purpose of this review is to collect the applications in fine synthesis of hypophosphite derivatives as reducing agents.

A novel and facile preparation of bremazocine enantiomers through optically pure N-norbremazocines

In order to provide ready access to multigram quantities of the optically pure bremazocines [(-)- and (+)-9,9-dimethyl-5-ethyl-2-hydroxy-2-(1-hydroxy-cyclopropylmethyl)-6,7-benzomorphan)], we have developed an improved non-chromatographic synthesis, and determined the optical purity of their N-nor precursors using a rapid and relatively simple 1H NMR method based on diastereomeric derivatization with optically pure 1-phenylethylisocyanate. This method of determining optical purity should be readily amenable to similar systems containing phenolic amino functionalities. Finally, a greatly simplified methodology for introduction of the N-(1-hydroxycyclopropylmethyl) substituent in bremazocine is described. The improved synthetic method-the overall yield was increased about 3-fold-combined with the practical methodology to determine optical purity will considerably facilitate the employment of these enantiomers as pharmacological tools for examination of the kappa-opioid receptor system, as well as their evaluation as drug abuse treatment agents. This synthesis will also enable the study of these enantiomers for other, non-classical applications (e.g., treatment agents for HIV).

Radiosynthesis of [11C]Lu 29-024: a potential radiotracer for 5HT2 receptors PET studies

For mapping 5-HT2 receptors in the central nervous system with positron emission tomography (PET), 2,5-dimethyl-3-(4-fluorophenyl)-1-(1-[11C]methyl-4-piperidinyl)-1H-indol e ([11C]Lu29-024) has been prepared. The precursor for the radiosynthesis of [11C]Lu29-024 was obtained in an overall yield of 53% by a convenient five-step synthesis; its reaction with [11C]methyl iodide afforded [11C]Lu29-024 in 35-50% radiochemical yield (decay corrected) in 45 to 50 min with a specific radioactivity ranging from 11 to 15 GBq/micromol. Following i.v. injections into rats, the analysis of plasma samples showed that the metabolism of [11C]Lu29-024 was rapid and extensive (60% of the original tracer was metabolized at 40 min). In contrast, only unmetabolized [11C]Lu29-024 could be detected in brain tissue. These biological results suggest that labeled metabolites have no access to brain tissue and further propose [11C]Lu29-024 as an interesting tool for PET studies of brain 5HT2 receptors.