Chuktabularins A-D, four new limonoids with unprecedented carbon skeletons from the stem bark of Chukrasia tabularis

Chuktabularins A-D (1-4), four novel 16-norphragmalin-type limonoids that feature unprecedented skeletons with a biosynthetically extended C2 or C3 unit at C-15 forming a unique 2,7-dioxabicyclo[2.2.1]heptane moiety, were isolated from the stem bark of Chukrasia tabularis. Their structures were elucidated by spectroscopic analysis and computer modeling. The biosynthetic pathway of 1-4 was postulated.