Identification of trans-3-Methyl-4-Decanolide in Blood Orange Juice and Mandarin Peel

Journal of Essential Oil Research: JEOR, Nov/Dec 2005 by Naef, Regula, Velluz, Alain

Abstract

trans-3-Methyl-4-decanolide has been identified in blood orange juice and in a mandarin peel extract, the spectral data and retention indices of the trans-3-methyl-4-decanolide and its cis-diastereoisomer are presented.

Key Word Index

Citrus sinensis, Citrus reticulate, Rutaceae, mandarin peel extract, blood orange juice, trans-3-methyl-4-decanolide.

Introduction

trans-3-Methyl-4-decanolide [1], a potent Iactone with a typical lactonic, coconut-like odor, was first identified by Maurer and Hauser in clary sage (1).

The cis-stereoisomer is a constituent of the African orchid Aerangiskirkii (2). 3-Methyl-4-decanolide without specification of the stereochemistry is mentioned in blood orange juice (3). Here we report the presence of the irans-isomer in a mandarin peel extract, attribute the same stereochemistry to the Iactone identified in blood orange juice, and describe the spectral data and retention times of both isomers. The enantiomeric form could not be determined. Mandarin peel oil and extracts have been thoroughly investigated, and recently the organoleptic importance of unsaturated aldehydes has been especially highlighted (see (4) and references cited therein).

Experimental

GC/MS was performed on a GC 6890 equipped with a polar column [Supelcowax, 30 m x 0.25 mm fused silica capillary column, film thickness 0.25 µm, 50°C (5 inin isotherm) at 5°/min to 240°C, carrier gas He, 63 kPa] coupled to a MS 5972 (Agilent) or a GC 6890 apolar column SPB-I [30 m x 0.25 nun fused silica capillary column, film thickness 1 µm, 60°C (5 min isotherm) at 5°/min to 250°C, carrier gas He, 63 kPa] coupled to a MS 5971 (Agilent). Linear retention indices (RI) were determined after injection of a series of n-alkanes under the same conditions.

The NMR-spectrawere measured in CDCl^sub 3^ with a Bruker WH 360 instrument with tetramethylsilane as internal standard, δ = 0.00 ppm. Preparation of the extract and the fractions of blood orange juice: see (1). Preparation of the extract and the fractions of mandarin peel extract: see (2). The mixture of cis-and trans-lactones were synthesized according to (1).

Analytical data of trans-3-methyl-4-decanolide: MS, 70 eV, m/z(rel. int.): 184[M]^sup ^(0), 166(1), 142(13), 124(7), 115(5), 99(100), 97(10), 86(3), 71 (27), 55(19), 43(33). ^sup 1^H-NMR (360 MHz, CDCl^sub 3^, TMS): δ0.90(t, 3H), δ1.14(d, 3H), δ1.25-1.35(m, 6H), δ1.35-1.45(m, 1H), δ1.45-1.75(m, 3H), δ2.15-2.30(m, 2H), δ2.60-2.70(m,1H), δ4.09(m, 1H). ^sup 13^C-NMR(90 MHz, CDCl^sub 3^): δ176.7(C-1), δ37.2(C-2), δ36.1(C-3), δ87.5(C-4), δ34.0(C-5), δ25.7(C-6), δ31.7(C-7), δ29.1(C-8), δ22.6(C-9), δ14.1(C-10), δ17,5(Me-C3). RI^sub polar^: 2085. RI^sub apolar^: 1469.

Analytical data of cis-3-methyl-4-decanolide: MS, 70 eV, m/z(rel. int.): 184[M^sup ^](0), 166(1), 142(13), 124(8), 115(9), 99(100), 97(16), 86(2), 71(26), 55(25), 43(38). ^sup 1^H-NMR (360 MHz, CDCl^sub 3^, TMS): δ0.90(t, 3H), δ1.01(d, 3H), δ1.25-1.32(m, 7H), δ1.45-1.70(m, 3H), δ2, 18(dxd, J^sub 1^=16.8, J^sub 2^=3.4, 1H), δ2.57(m, 1H), δ2.68(dxd, J^sub 1^ = 16.8, J^sub 2^=7.6, 1H), δ4.43(m, 1H). ^sup 13^C-NMR (90 MHz, CDCl^sub 3^): δ177.0(C-1), δ37.6(C-2), δ33.0(C-3), δ83.7(C-3), δ29.9(C-5), δ25.9(C-6), δ31.7(C-7), δ29.1(C-8), δ22.6(C-9), δ14.1(C-10), δ17.5(Me-C3). RI^sub polar^: 2155. RI^sub apolar^: 1500.

Results and Discussion

Only tran?s-3-methyl-4-decanolide has been identified in mandarin peel and orange juice. The cis-stereoisomer is described by Kaiser (2) to be present in the African orchid in contrast to its homologue, the oak- or whisky-lactone (3-methyl-4-octanolide) found in both configurations in oakwood (5), and consequently in brandies and wines aged in oak barrels (6).

The retention indices on the polar column (RI) of synthetic reference samples (1) could be determined as 2085 for the trans- and 2155 for the cis-stereoisomer. The stereochemistries of both isomers were attributed by ^sup 13^C-NMR-experiments with signals at 36.1 ppm for C-3 and 87.5 ppm for C-4 characteristic for the trans-isomer, and signals at 33.0 ppm for the C-3 and 83.7 ppm for the C-4 for the cis-isomer in agreement with the ^sup 13^C-NMR-values forthe oak-lactones (7). In Fraction 11 of the extract of blood orange juice (3) and Fraction 8 of the mandarin peel extract (4) the RI^sub polar^ of the lactone is 2084, indicating that the product in blood orange juice and mandarin peel extract is without doubt trans-3-methyl-4-decanolide.

References

1. B. Maurer and A. Mauser, New constituents of clary sage oil. In IXth Int. Congr. Essent. oils, 13-17, March 1983, Singapore, Book 3, p. 69-76 (1983).

2. R. Kaiser, The Scent of Orchids, p. 191, Elsevier, Editiones Roche, Basel (1993).

3. R. Naef, A. Velluz and A.P. Meyer, Volatile constituents of blood and blond orange juice: a comparison. J. Essent. Oil Res., 8, 587 (1996).

4. R. Naef and A. Velluz, Volatile constituents in extracts of mandarin and tangerine peel. J. Essent. Oil Res., 13, 154-157 (2001).

5. A. Mosandl, A. Kustermann, U. Palm, H.P. Dorau and W.A. König, Stereoisomeric flavour compounds. XXVIII. Direct chimspecific HRGC-analysis of natural γ-lactones, Z. Lebensm. Unters. Forsch., 188, 517-520 (1989).