Garcioblons A–F, Polycyclic Polyprenylated Acylphloroglucinols with Diverse Rearranged Skeletons from <i>Garcinia oblongifolia</i>

Garcioblons A-F (<b>1</b>-<b>6</b>), six unprecedented polycyclic polyprenylated acylphloroglucinols (PPAPs) formed via intramolecular Diels-Alder (IMDA) reactions from monocyclic polyprenylated acylphloroglucinols (MPAPs), were isolated from <i>Garcinia oblongifolia</i>. Their structures were elucidated through spectroscopic analysis and quantum calculations. Structurally, compound <b>1</b> is the first PPAP characterized by an unprecedented 6/6/5/7/6/5/6/5 octacyclic ring system with a 11-oxatetracyclo[8.5.1.0^1,12.0^5,10]hexadecane motif, while <b>2</b>-<b>4</b> are its biogenetically related analogues. Compound <b>5</b> possesses a caged 6-oxatetracyclo[7.3.1.1^2,10.0^2,7]tetradecane new carbon skeleton, while compound <b>6</b> features a 4-oxatricyclo[7.4.0.0^1,5]tridecane structure. Additionally, compound <b>1</b> demonstrated notable antitumor activities by inhibiting autophagic flux and stimulating oxidative stress, which collectively resulted in reduced cell proliferation and induced apoptosis.