The clove basil (Ocimum gratissimum) comes for Africa. Upon distillation, it yields an essential oil containing mainly eugenol and β-caryophyllene.
Circle H Institute is an organization dedicated to furthering the knowledge about hydrosols. Its manager, Ann Harman, contacted us after performing clove basil hydrodistillation using a copper apparatus. After standing for several months, flaky crystals formed from the clove basil hydrosol, which could not be identified using standard mass spectral databases.
We were provided a few hundred milligrams of the flakes and were able to study them. The mass spectrum of the sample did not remind of any classical class of essential oils constituents (figure 1), but the GC run showed that the crystals were likely a single molecule of high purity. They were thus submitted to nuclear magnetic resonance (NMR) experiments to determine its structure.
|Figure 2. 1H spectrum of deugenol, with zoomed section for the alcenic region. Numbering refers to figure 4.|
|Figure 3. APT (13C) spectrum of deugenol. Positive peaks indicate CH3 or CH groups, while negative peaks indicated CH2 or quaternary carbons. Numbering refers to figure 4.|
The following paragraph is more technical, and presented for the scientific reader.
Analyzis of the 1D spectra indicated the presence of two oxygenated methyls, four methylene, six methine and eight quaternary carbons. The DQF-COSY spectrum indicated that H-9, H-8 and H-7 were in the same spin system, with H-9 being a terminal alkene. This indicated an allyl moiety. H-7 showed HMBC correlations with C-1, C-2 and C-6, suggesting the C-7/C-1 bond. The HMBC correlations of meta doublets H-2 and H-6 completed an aromatic ring with C-3, C-4 and C-5. The H-10 methoxy group exhibits an HMBC correlation with C-3, while the alcoholic proton OH1 correlated with C-3, C-4 and quaternary C-5. This overall suggested a structure similar to eugenol, with quaternary C-5 bonded with itself to form a dimer. A summary of DQF-COSY and HMBC correlations is shown at figure 4.
|Figure 4. 2D NMR correlations of deugenol. Bold lines: COSY correlations; arrows: H→C HMBC correlations.|
Dieugenol is known to occur in clove (Syzygium aromaticum, syn. Eugenia caryophyllata)  and nutmetg (Myristica fragrans) . It usually is isolated by fractionation of non-volatile extracts, or produced by chemical synthesis, although up to now we have encountered no account of its formation in an aqueous medium.
Dieugenol. White crystals. 1H NMR (400 MHz, CDCl3) δ: 6.77 (d, J = 1.3, H-6), 6.74 (d, J = 1.3, H-2), 6.05 (s, OH), 6.00 (m, H-8), 5.11 (m, H-9), 3.93 (s, 10-OCH3), 3.38 (d, J = 6.55, H-7); 13C NMR (100 MHz, CDCl3) δ: 147.2 (C-3), 140.9 (C-4), 137.6 (C-8), 131.9 (C-1), 124.4 (C-5), 123.1 (C-6), 115.7 (C-9), 110.6 (C-2), 56.1 (10-OCH3), 40.0 (C-7); EI-MS m/z = 326, 297 (27), 327 (22), 165 (13), 244 (13), 115 (12), 229 (11), 152 (11).
Closing note: Laboratoire PhytoChemia is eager to pursue similar collaborations (for little to no cost) to widen knowledge about essential oils, hydrosols and derived products, as long as our time allows us to investigate the matter. If you have a research project idea that can lead to a publication, please contact us.
 M. Miyazawa and H. Masayoshi. Antimutagenic activity of phenylpropanoids from colve (Syzygium aromaticum), J. Agric. Food Chem. 2003, 51(22), 6413-6422.
 A. Isogai, S. Murakoshi, A. Suzuki and S. Tamura. Isolation from nutmeg of growth inhibitory substances to silkworm larvae, Agric. Biol. Chem., 1973, 37(4), 889-895.