Department of Chemistry Faculty of Science, Chulalongkorn University^* Department of Physics, Faculty of Science and Technology, Thammasat University, Bangkok, Thailand.^**
○Wilaiwon Tirawanich^* Thapong Teerawatananond^* Narongsak Chaichit^** Amorn Petsom^*

Two cembranoids, crotocembraneic acid, (1E,3E,7E,11Z)-1-isopropyl-4,8-dimethylcyclotetradeca-1,3,7,11-tetraene-12-carboxylic acid (1) and neocrotocembraneic acid, (1E,3E,7E,11E)-1-isopropyl-4,8-dimethylcyclotetradeca-1,3,7,11-tetraene-12-carboxylic acid (2), C₂₀H₃₀O₂, were isolated from Croton oblongifolius Roxb. which had been used as Thai traditional medicine to treat human gastrointestinal track. In this work, we revealed their differences in Z- and E- molecular configurations by X-ray analysis. Cembranoids 1 and 2 were crystallized in space groups monoclinic P2₁/a and triclinic P(1) with their unit cell parameters a=9.8513(5)Å, b=10.5630(10)Å, c=18.5873(11)Å, β=102.136(2)ﾟ and α=7.64120(10)Å, b=9.7269(2)Å, c=13.11200(10)Å, α=95.387(0)ﾟ, β=98.222(1)ﾟ, γ=98.899(1)ﾟ. Dihedral angles C10-C11-C12-C13 of 1 and 2 were -175.24(0.30)ﾟ and -2.08(0.30)ﾟ, respectively. Both stereoisomers formed a pair of inter-molecular hydrogen bonding between the hydroxyl and carbonyl groups. The crystal packing of 1 showed the O2H…O1 hydrogen bond distance of 2.626(3)Å, which was slightly shorter than a hydrogen bond of 2.6433(19)Å in molecular crystal 2.

Reference

[1] Roengsumran S., Achayindee S., Petsom A., Pudhom K., Singtothong P., Surachetapan C., Vilaivan T., Two new cembranoids from Croton oblongifolius, J. Nat. Prod., 61, (1998), 652-654.