Synthesis of deuterium labeled NMDA receptor inhibitor-20-Oxo-5 beta-[9,12,12-H-2(3)]pregnan-3 alpha-yl-L-glutamyl 1-ester
Abstract
20-Oxo-5 beta-[9,12,12-H-2(3)]pregnan-3 alpha-yl-L-glutamyl 1-ester 11 was synthesized as an internal standard for quantification of a neuroprotective NMDA receptor ligand, 20-oxo-5 beta-pregnan-3 alpha-yl-L-glutamyl 1-ester 18 and its metabolites, in plasma and tissue. 11 alpha-Hydroxy-progesterone (1) was reduced under basic conditions to yield the corresponding 5 beta-steroid. Protection of the 3- and 20-oxo groups and oxidation of the 11 alpha-hydroxy group was then followed by a deuterium exchange, conducted under basic conditions using deuterated methanol.
Next, the carbonyl moiety at C-11 was reduced and the 11 alpha-hydroxyl group removed through utilization of the Barton-McCombie reaction. Subsequent deprotection of the 3- and 20-acetals and stereoselective reduction of the 3-oxo group gave the desired trideuterated pregnanolone (8).
This was coupled with protected glutamic acid, which was then deprotected to yield [9,12,12-H-2(3)]-pregnanolone glutamate (11) with >99% isotopic purity.