The results showed that the BDE value of ent-16(S)-18-acetoxy-7 -hydroxykaur-15- one compound is the lowest, being kcal/mol. Among substituents binding at C16 position of this molecule, –NH2 has the most remarkable influence on the BDE (C H) value. | Vietnam Journal of Science and Technology 56 (4A) (2018) 46-52 EFFECTS OF SUBSTITUENTS ON C H BOND DISSOCIATION ENTHALPIES OF ENT-KAURANE DITERPENOIDS: A DFT STUDY Ngo Dang Truong Hai1, Ngo Thi Chinh2, *, Pham Minh Quan3, *, Dao Duy Quang2 1 Faculty of Pharmacy, Duy Tan University, 254 Nguyen Van Linh, Thac Gian, Thanh Khe dist., Da Nang city 2 Institute of Research and Development, Duy Tan University, 254 Nguyen Van Linh, Thac Gian, Thanh Khe dist., Da Nang city 3 Institute of Natural Products Chemistry, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Ha Noi * Email: minhquanaries@; Received: 1 August 2018; Accepted for publication: 13 October 2018 ABSTRACT C H bond dissociation enthalpies (BDEs) of seven ent-kaurane diterpenoids extracted from Croton tonkinensis Gagnep. have been investigated by using density functional theory (DFT) method. The calculations were performed at the M05-2X/6-31+G(d) level of theory. Additionally, insight into the effects of different substituents including –NH2, –OH, –NO2, –SH, –CN, –Cl, –CONH2, –CH-(CH3)2, –NHCOCH3, –OCOCH3 and –C2H5 on BDE have also been provided. The results showed that the BDE value of ent-16(S)-18-acetoxy-7 -hydroxykaur-15one compound is the lowest, being kcal/mol. Among substituents binding at C16 position of this molecule, –NH2 has the most remarkable influence on the BDE (C H) value. Indeed, the BDE of C16 H significantly decreases from to kcal/mol when replacing –CH3 group by –NH2 one at the C16 position. The obtained results may provide more information for organic synthesis of ent-kaurane based – novel antioxidant compounds. Keywords: DFT, BDE, ent-kaurane diterpenoids, substituent, antioxidant. 1. INTRODUCTION The genus Croton L. (Euphorbiaceae) comprises of about 800 species which were primarily found in tropical areas among which 31 species are distributed in Vietnam [1]. Croton tonkinensis Gagnep., locally known as “Kho sam Bac Bo” .
