Subscribe to RSS
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
(-)-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.
δ C |
δ H |
Position |
171.9 |
––––––– |
8 |
182.5 |
–––––––- |
6 |
47.3 |
1.76 dd* |
2 |
45.6 |
1.52 dd (14.5, 3.6) |
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.