Synthesis and NMDA-receptor affinity of 4-oxo-dexoxadrol derivatives

Examining the effect of regioisomerism on the physico-chemical properties of lysophosphatidylethanolamine-containing liposomes using fluoro probes

Lysophospholipids (LysoPLs) receive steadily increasing attention in the area of lipid chemistry and biology. However, the physico-chemical properties of individual LysoPL regioisomers have not yet been investigated. Herein, we report the synthesis of fluoro analogues of lysophosphatidylethanolamines (LPEs) and examine the physico-chemical properties of the LPE regioisomers using chemically synthesized fluoro probes.

Solid-Phase Organic Synthesis of Dexoxadrol Analogues

A solid-phase synthesis of dexoxadrol analogues like-13 and unlike-13 bearing an oxo group in the 4-position of the piperidine ring has been developed using aminomethyl substituted polystyrene resin as solid support. The synthesis comprises a hetero-Diels–Alder reaction of imine 7b with Danishefsky’s diene 8 in the presence of the Lewis acid Yb(OTf)3 and a conjugate reduction of the double bond of 9b with LiBHEt3 and BF3. The cleavage of the product from the solid support was performed with 1-chloroethyl chloroformate. All transformations on the solid support and additionally the cleavage reaction had to be compatible with the large and acid labile acetalic 1,3-dioxolane moiety in 2-position of the piperidine ring. The oxodexoxadrol derivative 12 was obtained in an overall yield of 17 %.

Synthesis of 4-(aminoalkyl) substituted 1,3-dioxanes as potent NMDA and σ receptor antagonists

Elongation of the distance between the oxygen heterocycle and the basic amino moiety or ring expansion of the oxygen heterocycle of the NMDA receptor antagonists dexoxadrol and etoxadrol led to compounds with promising NMDA receptor affinity. Herein the combination of both structural features, i.e. elongation of the O-heterocycle--amine distance with a 1,3-dioxane ring is envisaged. The synthesis of aminoethyl-1,3-dioxanes 13, 22, 23 and 29 was performed by transacetalization of various acetals with pentane-1,3,5-triol, activation of the remaining free OH moiety with tosyl chloride and subsequent nucleophilic substitution. The corresponding 3-aminopropyl derivatives 33-35 were prepared by substitution of the tosylates with KCN and LiAlH4 reduction. The highest NMDA receptor affinity was found for 1,3-dioxanes with a phenyl and an ethyl residue at the acetalic position (23) followed by diphenyl (22) and monophenyl derivatives (13). Generally the NMDA affinity of primary amines is higher than the NMDA affinity of secondary and tertiary amines. Altogether the primary amine 23a (Ki=24 nM) represents the most promising NMDA receptor antagonist of this series exceeding the NMDA affinity of the mono-homologues (2-aminoethyl)-1,3-dioxolanes (3,4) and (aminomethyl)-1,3-dioxanes (5,6). Whereas the primary amine 23a turned out to be selective against σ1 and σ2 receptors the benzylamine 13d was identified as potent (Ki=19 nM) and selective σ1 antagonist, which showed extraordinarily high antiallodynic activity in the capsaicin assay.