Synthesis and evaluation of C8-substituted 4.5-spiro lactams as Glycogen Phosphorylase a inhibitors

An effective synthesis of 4.5-spiro lactams 28/29, has been completed in nine steps with an overall yield of 5.8%. The 4.5-spiro lactams were made from 2-allyl-Cbz-Pro-OMe 21, which was converted into the corresponding alcohol 22 via a hindered borane reaction with (2-methylbutyl)₂borane. Subsequent Swern oxidation of 22 gave novel aldehyde 23. Aldehyde 23 was treated under Bucherer-Bergs reaction conditions to give hydantoin 26, which was opened to the corresponding amino acid 30 using di-tert-butyl dicarbonate and DMAP followed by hydrolysis. Treatment of amino acid 30 with acidic methanol gave 4.5-spiro lactams 28/29. Only 4.5-spiro lactam 29 displayed moderate activity against GPa with an IC₅₀ of 241 μM.