Condensation derivatives of 4-isopropylbenzaldehyde with acetophenone from the red alga Laurencia tristicha

Abstract

Seven undescribed condensation derivatives of 4-isopropylbenzaldehyde with acetophenone, including one 1,3,5-trisubstituted pentane-1,5-dione, two 1,3,4,5,7-pentasubstituted heptane-1,7-diones and four 1,2,3,4,5-pentasubstituted cyclohexanols, together with two known flavonoids, were obtained from the red alga Laurencia tristicha. The relative configurations were elucidated by extensive spectroscopic data analysis of MS, 1D and 2D NMR, while the absolute configurations were determined by comparing the experimental and calculated electronic circular dichroism spectra. All the isolates were proven to be naturally occurring in the red alga by LC-MS analysis, and these 1,3,5-trisubstituted-pentane-1,5-dione, 1,3,4,5,7-pentasubstituted-heptane-1,7-diones and 1,2,3,4,5-pentasubstituted-cyclohexanols were reported from natural sources for the first time. The proposed biogenetic pathway of the isolates was also discussed.

Keywords: 1,2,3,4,5-Pentasubstituted cyclohexanol; 1,3,4,5,7-Pentasubstituted heptane-1,7-dione; 1,3,5-Trisubstituted pentane-1,5-dione; Laurencia tristicha; Red alga; Rhodomelaceae.