Biomimetic Synthesis Guides The Isolation Of Trace Meroterpenoids From Psidium Guajava

This thesis mainly focuses on the biomimetic synthesis of psiguajdianone,which is a novel dimer of caryophyllene-derived meroterpenoid isolated from P.guajava.All contents are divided into three chapters below.Chapter 1 Studies on Psidium meroterpenoids:Due to the perfect bioactivity and novel skeleton of Psidium meroterpenoids,the attention of chemists engaged in the isolation or synthesis of natural products was always drawn toward new Psidium meroterpenoids.This chapter outlines the isolation and diverse bioactivity research of41 Psidium meroterpenoids and the synthesis of some of them since 2007.Chapter 2 Studies on the biomimetic synthesis of psiguajdianone:Initially,the isolation of psiguajdianone with an unusual skeleton from the dried leaves of P.guajava was presented.To solve two problems,structure elucidation of psiguajdianone and construction of adjacent quaternary carbon centers,we decided to synthsize it.Based on the strategy of biomimetic synthesis,the synthetic procedure involved two key steps,1)an anhydrous three component coupling reaction between?-caryophyllene,paraformaldehyde and a known phloroglucinol derivative,and 2)a radical dimerization reaction.Chapter 3 The isolation and structure elucidation of key intermediates and by-products from Psidium guajava:Due to the application of biomimetic strategy in total synthesis,the key intermediates and by-products were consist with the plausible biosynthetic precursors of psiguajdianone;So it revealed the key intermediates and by-products should be natural products,which exist in P.guajava.With all key intermediates and by-products in hand,we next focused on the isolation of the corresponding natural products guided by these synthetic products.Significantly,five new natural compounds and two known ones were isolated from leaves of P.guajava.Five new natural products were psiguajanone A?1.3 mg?,psiguajanone B?1.1 mg?,psiguajanone C?7.7 mg?,psiguajanone D?3.8 mg?and psiguajanol A?1.4 mg?,and another two compounds were guapsidial A?1.0 mg?,psiguajadial D?1.2 mg?.Studies indicate that psiguajdianone showed cytotoxic activity against HepG2 and Hela cell lines,with half maximal inhibitory concentration(IC₅₀)values of 27.90 and28.14?mol/L,respectively.