Interpretation of methylene-proton NMR signals of 1,3-dimethyl-substituted alkyl chains

Unraveling the unknown: Interpretation of methylene-proton NMR signals of 1,3-dimethyl-substituted alkyl chains allows for the assignment of the relative ...





Assignment of Relative Configuration of Desoxypropionates by ¹H NMR Spectroscopy: Method Development, Proof of Principle by Asymmetric Total Synthesis of Xylarinic Acid A and Applications (pages 7071–7081)

Dr. Yvonne Schmidt, Dipl.-Chem. Konrad Lehr, Lucie Colas and Prof. Dr. Bernhard Breit

Article first published online: 27 APR 2012 | DOI: 10.1002/chem.201103988

Unraveling the unknown: Interpretation of methylene-proton NMR signals of 1,3-dimethyl-substituted alkyl chains allows for the assignment of the relative configuration of the two adjacent stereogenic centers (see figure). The new method is applicable in various NMR solvents and general trends and rules for assignment are shown. Natural products with unknown configuration can be assigned by using the information gained from already published spectra.

Corrected by:

Corrigendum: Corrigendum: Assignment of Relative Configuration of Desoxypropionates by 1H NMR Spectroscopy: Method Development, Proof of Principle by Asymmetric Total Synthesis of Xylarinic Acid A and Applications

Vol. 18, Issue 45, 14226, Article first published online: 25 OCT 2012







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Oleanolic acid spectral data and interpretation

Oleanolic acid
(4aS,6aR,6aS,6bR,8aR,10S,12aR,14bS)-10-hydroxy-2,2,6a,6b,9,9,12a-heptamethyl-1,3,4,5,6,6a,7,8,8a,10,11,12,13,14b-tetradecahydropicene-4a-carboxylic acid

Oleanic acid, Caryophyllin, Astrantiagenin C, Giganteumgenin C, Virgaureagenin B, 3beta-Hydroxyolean-12-en-28-oic acid, OLEANOLIC_ACID

Molecular Formula: C₃₀H₄₈O₃   

Molecular Weight: 456.70032  

Ursolic acid [(3b)-3-Hydroxyurs-12-en-28-oic acid] rarely occurs without its isomer oleanolic acid [(3b)-3-Hydroxyolean-12-en-28-oic acid] They may occur in their free acid form, as shown in Figure 1, or as aglycones for triterpenoid saponins which are comprised of a triterpenoid aglycone linked to one or more sugar moieties. Ursolic and oleanolic acids are similar in pharmacological activity

A pentacyclic triterpene that occurs widely in many PLANTS as the free acid or the aglycone for many SAPONINS. It is biosynthesized from lupane. It can rearrange to the isomer, ursolic acid, or be oxidized to taraxasterol and amyrin.   


MS
EIMS m/z (rel. int.) 456 [M]+ (5), 412 (3), 248 (100), 203 (50), 167 (25), 44 (51)


IR KBR
(KBr) 3500, 2950, 2850, 1715; 1H-NMR (250 MHz, pyridine-d5) δ: 5.49 (1H, s, H-12), 3.47 (1H, t, J = 8.0 Hz, H-3), 3.30 (1H, m, H-18), 1.12 (3H, s, CH3-27), 0.96 (3H, s, CH3-30), 0.91 (3H, s, CH3-25), 0.89 (3H, s, CH3-23), 0.87 (3H, s, CH3-24), 0.75 (3H, s, CH3-26)







1H NMR

(250 MHz, pyridine-d5) δ: 5.49 (1H, s, H-12), 3.47 (1H, t, J = 8.0 Hz, H-3), 3.30 (1H, m, H-18), 1.12 (3H, s, CH3-27), 0.96 (3H, s, CH3-30), 0.91 (3H, s, CH3-25), 0.89 (3H, s, CH3-23), 0.87 (3H, s, CH3-24), 0.75 (3H, s, CH3-26)

13 C NMR

(63 MHz, pyridine-d5) δ: 180.2 (C-28), 144.8 (C-13), 122.5 (C-12), 78.0 (C-3), 55.7 (C-5), 48.0 (C-9), 46.6 (C-8, 17), 42.1 (C-14), 39.7 (C-4), 39.4 (C-1), 37.3 (C-10), 33.2 (C-7), 32.9 (C-29), 32.4 (C-21), 30.9 (C-20), 28.7 (C-23), 27.2 (C-2), 26.9 (C-15), 26.1 (C-30), 23.7 (C-11), 23.6 (C-16), 18.7 (C-6), 17.4 (C-26), 16.5 (C-24), 15.5 (C-25)

http://www.google.com/patents/US20120237629

FIG. 4 shows the ¹H NMR spectrum of oleanolic acid;

FIG. 5 shows the ¹³C NMR spectrum of oleanolic acid;

FIG. 6 shows the ¹³C DEPT NMR spectrum of oleanolic acid;

FIG. 7 shows the ¹H ¹³C HSQC NMR spectrum of oleanolic acid;

see below

EXAMPLE 2 Extraction and Isolation of Oleanolic Acid (9) and Maslinic Acid (10) from Cloves

Syzygium aromaticum dried buds or whole cloves were obtained commercially. The cloves (1.5 kg, whole) of Syzygium aromaticum were sequentially and exhaustively extracted with hexane and ethyl acetate to give, after solvent removal in vacuo, a hexane extract (68.8 g, 4.9%) and an ethyl acetate extract (34.1 g, 2.3%). A portion of the ethyl acetate extract (10.0 g), was subjected to chromatographic separation on silica gel (60-120 mesh) column (40×5.0 cm). Elution with hexane/ethyl acetate solvent mixtures (8:2→6:4) afforded pure oleanolic acid (9) (4.7 g, 1.06%), a mixture of oleanolic acid (9) and maslinic acid (10) (0.5 g), and pure maslinic acid (10) (0.25 g). The structures of oleanolic acid (9) and maslinic acid (10) (as 2,3-diacetoxyoleanolic acid) were confirmed by spectroscopic data analysis (1D and 2D ¹H NMR and ¹³C NMR experiments) (FIGS. 4-7 and FIGS. 8-10, respectively).