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Starting from pyroglutamic acid, the synthesis of spiro-bis-γ-lactams, using as key step a chemoselective Michael reaction of pyroglutamates is reported. Thus, the reaction of N-BOC- l -methyl pyroglutamate with LiHMDS gives the enolates at C4 which react with several Michael acceptors. On the other hand, N-benzyl- l -methyl pyroglutamate reacts under the same conditions, to give the ester enolate which reacts with Michael acceptors leading to quaternized derivatives. The synthesis of the bicyclic spirolactams results from a reduction of the nitro group present in these derivatives which directly gives the spiro compounds. These final compounds may act as β-turn mimetics, as they have torsion angles which are in the range of β-turns of type II and II′. |
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