A Straightforward Stereoselective Synthesis of d- and l-5-Hydroxy-4-hydroxymethyl-2-cyclohexenylguanine

A novel and facile synthesis of 5-hydroxy-4-hydroxymethyl-2-cyclohexenylguanine 1 is described. The key steps involve a Diels−Alder reaction of ethyl (2E)-3-acetyloxy-2-propenoate 2 as dienophile with Danishefsky's diene 3 to build up the six-membered ring skeleton, a Fraser-Reid reductive rearrangement of the adduct using LiAlH4, and base-moiety introduction using a Mitsunobu reaction. Optically pure d- and l-1 were obtained via resolution of intermediate 7 with (R)-(−)-methylmandelic acid. The synthetic procedure toward racemic 1 consists of only five steps and has proven to be highly efficient toward the synthesis of cyclohexenyl nucleosides

Synthesis of an 11-unsubstituted analogue of (±)-huperzine A

The synthesis of a new analogue of (±)-huperzine A lacking the ethylidene appendage at position 11 has been accomplished. The key steps of the synthesis were: a) the reduction of the keto function of the known methyl 7,7-ethylenedioxy-3-methyl-9-oxobicyclo[3.3.1]non-3-ene-1-carboxylate into a methylene group by reduction to a mixture of stereoisomeric alcohols follwed by alcohol-deoxygenation through a Barton-McCombie proccdure and b) the elaboration of the pyridone ring in a late stage of the synthesis by reaction of a pyrrolidine enamine with propiolamide, which gave a mixture of regioisomeric pyridone derivatives

Enantioselective synthesis of tacrine–huperzine A hybrids. Preparative chiral MPLC separation of their racemic mixtures and absolute configuration assignments by X-ray diffraction analysis

A new synthesis of racemic 7-substituted bicyclo[3.3.1]non-6-en-3-ones, rac-4, whose key-step involves the reaction of a vinyl triflate, rac-7, with an organometallic reagent, has been developed. This procedure has been applied to the enantioselective synthesis of (+)- and (−)-7-ethylbicyclo[3.3.1]non-6-en-3-one, (+)- and (−)-4b, from which both enantiomers of the cholinesterase inhibitor, tacrine–huperzine A hybrid, 9b, have been obtained. Rac-9b and its related compounds rac-9a and rac-10a were separated into their enantiomers on a preparative scale by medium pressure liquid chromatography (MPLC) using microcrystalline cellulose triacetate as the chiral stationary phase. X-ray diffraction analysis of (−)-10a as the o-iodobenzoic acid salt, allowed us to establish its absolute configuration and deduce those of other enantiopure tacrine–huperzine A hybrids

Easy synthesis of 7-alkylbicyclo[3.3.1]non-6-en-3-ones by silica gel-promoted fragmentation of 3-alkyl-2-oxaadamant-1-yl mesylates

A synthesis of 7-alkylbicyclo[3.3.1]non-6-en-3-ones4b-f and 4j, k by reaction of the corresponding 3-alkyl-2-oxaadamant-1-yl mesylates3 with silica gel in methylene chloride at room temperature, is described. The method failed to give enones4a, g and the related compounds4l, m, what can be rationalized on mechanistic grounds. The synthesis of several bicyclic enones4 from the readily available diketones1a-c [X = CH2, (CH3O)2C, (CH3O)(CH3)C] via the corresponding oxaadamantanols2 and mesylates3, is described

Synthesis and antiviral activity of a series of new cyclohexenyl nucleosides

A series of new cyclohexenyl nucleosides is synthesized by coupling the heterocyclic bases with a protected cyclohexenyl precursor under Mitsunobu conditions. The compounds were evaluated for their antiviral and cytostatic activity. Pronounced activity against herpes simplex virus type 1 and type 2 was observed for the 2,6- diaminopurine analogue

Synthesis and Biological Evaluation of a Series of New Cyclohexenyl Nucleosides

A series of cyclohexenyl nucleosides (1-8) were successfully prepared with moderate yield and their cytotoxicity and antiviral activity were investigated. Among the eight new compounds, only the diaminopurine analogue 8 showed pronounced activity against HSV-1, HSV-2.status: publishe

Huprine X is a Novel High-Affinity Inhibitor of Acetylcholinesterase That Is of Interest for Treatment of Alzheimer's Disease

Inhibitors of the enzyme acetylcholinesterase (AChE) slow and sometimes reverse the cognitive decline experienced by individuals with Alzheimer's disease. Huperzine A, a natural product used in traditional Chinese herbal medicine, and tacrine (Cognex) are among the potent AChE inhibitors used in this treatment, but the search for more selective inhibitors continues. We report herein the synthesis and characterization of (−)-12-amino-3-chloro-9-ethyl-6,7,10,11-tetrahydro-7,11-methanocycloocta[b]quinoline hydrochloride (huprine X), a hybrid that combines the carbobicyclic substructure of huperzine A with the 4-aminoquinoline substructure of tacrine. Huprine X inhibited human AChE with an inhibition constantK I of 26 pM, indicating that it binds to this enzyme with one of the highest affinities yet reported. Under equivalent assay conditions, this affinity was 180 times that of huperzine A, 1200 times that of tacrine, and 40 times that of E2020 (donepezil, Aricept), the most selective AChE inhibitor currently approved for therapeutic use. The association and dissociation rate constants for huprine X with AChE were determined, and the location of its binding site on the enzyme was probed in competition studies with the peripheral site inhibitor propidium and the acylation site inhibitor edrophonium. Huprine X showed no detectable affinity for the edrophonium-AChE complex. In contrast, huprine X did form a ternary complex with propidium and AChE, although its affinity for the free enzyme was found to be 17 times its affinity for the propidium-AChE complex. These data indicated that huprine X binds to the enzyme acylation site in the active site gorge but interferes slightly with the binding of peripheral site ligands

New Syntheses of rac-Huperzine A and its rac-7-Ethyl-Derivative. Evaluation of Several Huperzine A Analogues as Acetylcholinesterase Inhibitors

rac-Huperzine A, its rac-7-ethyl-derivative and two regioisomeric analogues have been prepared through synthetic sequences involving the elaboration of the pyridone ring in a late stage, by reaction of an intermediate pyrrolidine enamine with propiolamide, which gave mixtures of regioisomeric pyridone derivatives. The acetylcholinesterase inhibitory activity of these and two other recently described 11-unsubstituted huperzine A analogues was determined, the rac-7-ethyl analogue of huperzine A being the most active compound, although it is about 12-fold less active than (−)-huperzine A