The use of high‐field carbon‐13 NMR spectroscopy to characterize chiral centers in isopranes

Abstract

The 13C nuclear magnetic resonance spectra of four diastereomeric, acyclic isoprenoids [farnesane (C15), pristane (C19), phytane (C20), and squalane (C30)] have been obtained as a means for interpreting hydrocarbon mixtures common in some fossil fuels and biosynthesized organic compounds. Multiple resonance environments were detected for carbons influenced by two or three chiral centers. Samples of farnesane and squalane were found to exhibit random stereochemistry, whereas the phytane sample was demonstrated to be a mixture of two isomers, probably the 6(R), 10(S), 14(R,S) compound. The sample of pristane consisted of a single diastereomer and was probably obtained from a natural product. It is shown that general chemical shift assignments can be made in this class of molecules by considering the number of carbons located at positions one, two and three bonds distant, while assignment of closely spaced lines may be made on the basis of diastereomerically induced chemical shifts. Using these principles, the structural features of two fossil fuels were analysed.

Betulinic Acid Suppresses Ovarian Cancer Cell Proliferation through Induction of Apoptosis

“…Thus, the hexane-soluble fraction was subjected to repeated column chromatography and preparative HPLC isolation, which afforded the isolation of 14 compounds, including seven triterpenoids ( 2 – 4 , 6 , 7 , 9 , 11 ), five steroids ( 5 , 10 , 12 – 14 ), and two diterpene analogs ( 1 and 8 ) (Figure 2). The chemical structures of all the isolates were determined and they were identified as norphytan ( 1 ) [16], leucophyllone ( 2 ) [14], 3- O -acetylbetulin ( 3 ) [17], betulinic acid methyl ester ( 4 ) [18], 6 β -hydroxysitostenone ( 5 ) [19], lupenone ( 6 ) [20], methyl 3- O -acetylbetulinate ( 7 ) [21], phytone ( 8 ) [22], lupeol ( 9 ) [23], sitostenone ( 10 ) [24], betulinic acid ( 11 ) [25], 5 α -stigmast-3,6-dione ( 12 ) [26], 3 β -sitostanol ( 13 ) [27], and 6 α -hydroxy- β -sitostenone ( 14 ) [28] by comparison of their spectroscopic data, including 1 H and 13 C NMR (see the Supplementary Materials), and physical data with previously reported values, and LC/MS analysis. Compounds 1 , 5 , 8 , 10 , and 12–14 were isolated and identified for the first time from C. walteri .…”

Quantitative determination of aliphatic hydrocarbon compounds by 2D NMR

“…Chirality of squalane can be seen from the 5, 7, 9, 11 carbon shifts caused by various diastereomers. 11 Protons of those methylene groups are not equivalent, which can be seen in the F 1 dimension.…”

Identification of Bioactive Natural Product from the Stems and Stem Barks of Cornus walteri: Benzyl Salicylate Shows Potential Anti-Inflammatory Activity in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages

“…Phytochemical analysis of the hexane fraction was carried out by applying column chromatography and high-performance liquid chromatography (HPLC) as well as LC/MS analysis. Semi-preparative HPLC separation yielded 15 compounds ( Figure 1 ): 5α-stigmast-3,6-dione ( 1 ) [ 23 ], 3β-sitostanol ( 2 ) [ 24 ], 6α-hydroxy-β-sitostenone ( 3 ) [ 25 ], 6β-hydroxysitostenone ( 4 ) [ 26 ], norphytan ( 5 ) [ 27 ], phytone ( 6 ) [ 28 ], methyl 3- O -acetylbetulinate ( 7 ) [ 29 ], 3- O -acetylbetulin ( 8 ) [ 30 ], sitostenone ( 9 ) [ 31 ], leucophyllone ( 10 ) [ 16 ], lupeol ( 11 ) [ 32 ], lupenone ( 12 ) [ 33 ], betulinic acid ( 13 ) [ 34 ], betulinic acid methyl ester ( 14 ) [ 35 ], and benzyl salicylate ( 15 ) [ 36 ]. The structures of compounds 1 – 15 ( Figure 2 ) were determined by comparing their 1 H and 13 C NMR spectra with those previously reported in the literature [ 16 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ], and by LC/MS analysis.…”