Planta Med 2016; 82 - PC50
DOI: 10.1055/s-0036-1578752

A Deep Look Inside The NMR Data Of (-) Loliolide: Confusion About The Assignment Of Carbonyl Carbon And The Methylene Protons

A Moawad 1
  • 1Pharmacognosy Department, Faculty of Pharmacy, Beni-Suef University, Beni-Suef, 62514, Egypt

(-)-Loliolide is monoterpene lactone that has been described to be a potent ant-repellent [1]. It was considered as a biosynthetic degradative product of terpenoids [2]. Looking at the reported NMR data of this simple compound; exchange was found between the assignment of C-6 and C-8 [3]. In addition confusion about the methylene groups' pair of protons was also found [4]. This compound shows a unique carbon assignment of an SP 2 quaternary carbon which is not attached to a heteroatom at δC 182.5 ppm and also a long rang coupling (4-bond) between two of the methylene protons at C-2 and C-4 making these protons appear as a doublet of triplets. Also some correct data were found [5, 6, and 7]. The correct assignment is presented.

Fig. 1

Tab. 1: The correct assignment of selected protons and carbons of (-) – loliolide (CDCl3).

δ C

δ H

Position

171.9

–––––––

8

182.5

–––––––-

6

47.3

1.76 dd*
2.46 dt (14.5, 2.5)

2

45.6

1.52 dd (14.5, 3.6)
1.98 dt (14.5, 2.5)

4

*Masked by methyl peak, but could be observed as dd from its HSQC correlation

1 H (400 MHz) and 13C (100 MHz), J value between brackets

References:

[1] Okunade AL et al. (1985)J Nat Prod 48:472 – 473.

[2] Devon TK, Scott AI. (1972) Handbook of Naturally Occurring Compounds. Volume II. Academic Press New York and London.

[3] Valdes LJ. (1986). J Nat Prod 49:171.

[4] Elkhayat ES. (2009) Bull Pharm Sci, Assiut Univ 32:189 – 197.

[5] Eidman KF, et al. (2006). J Org Chem 71:9513 – 9516.

[6] Xiao Y, et al. (2007). Chinese J Chem 25:661 – 665.

[7] Erosa-Rejón G, et al. (2009). J Mex Chem Soc 53:44 – 47.