5-( 6-Hydroxy-6-methyl-5-oxoheptan-2-yl )-2-methyl Phenyl Acetate

We synthesized a novel compound, 5-(6-hydroxy-6-methyl-5-oxoheptan-2-yl)-2-methylphenyl acetate, in a good yield by oxidation of 1-O-acetyl-xanthorrizol using potassium permanganate in acidic condition. The structure was elucidated by Fourier Transform Infrared (FTIR), 1H-Nuclear Magnetic Resonance (NMR) and 13C-NMR, two-dimensional (2D)-HSQC, Distortionless Enhancement by Polarization Transfer (DEPT), 2D-Heteronuclear Multiple Bond Correlation (HMBC), and High-Resolution Mass Spectra (HRMS) spectral data.

The Fourier Transform Infrared (FTIR) spectrum of the compound 2 exhibited the appearance of hydroxyl, carbonyl ester, and carbonyl ketone bands at 3482, 1762, and 1710 cm −1 .In the 1 H-NMR spectrum, the appearance of a singlet peak at δ 3.71 ppm confirmed the formation of the hydroxyl group, while the presence of two singlet peaks at δ 1.26 and 1.27 ppm indicated that the two methyl group bound to quaternary carbon.In the 13 C-NMR spectrum, the appearance of peaks at δ 214.6 and 76.3 ppm confirmed the formation of ketone (C=O) and C-O aliphatic groups [14,15].Furthermore, in Distortionless Enhancement by Polarization Transfer (DEPT) spectrum showed that carbon peak at δ 76.3 ppm was a quaternary carbon.The structure was supported by a two-dimensional (2D) Heteronuclear Multiple Bond Correlation (HMBC) spectrum displaying correlations between proton on a hydroxyl group at δ 3.71 ppm with thecarbon at δ 76.3, 26.6, and 26.5 ppm; protons on two methyl groups at δ 1.26 and 1.27 ppm with the carbon at δ 76.3 ppm; and other proton-carbon correlations due to two-bonds-four-bond couplings [14] (Figure 1 and Table 1), and a High-Resolution Electrospray Ionization Mass Spectometry (HRESIMS), which showed a molecular ion peak at m/z 315.1563 ([M + Na] + ).All data obtained are in entire agreement with the structure of the title compound.[14,15].Furthermore, in Distortionless Enhancement by Polarization Transfer (DEPT) spectrum showed that carbon peak at δ 76.3 ppm was a quaternary carbon.The structure was supported by a two-dimensional (2D) Heteronuclear Multiple Bond Correlation (HMBC) spectrum displaying correlations between proton on a hydroxyl group at δ 3.71 ppm with thecarbon at δ 76.3, 26.6, and 26.5 ppm; protons on two methyl groups at δ 1.26 and 1.27 ppm with the carbon at δ 76.3 ppm; and other proton-carbon correlations due to two-bonds-four-bond couplings [14] (Figure 1 and Table 1), and a High-Resolution Electrospray Ionization Mass Spectometry (HRESIMS), which showed a molecular ion peak at m/z 315.1563 ([M + Na] + ).All data obtained are in entire agreement with the structure of the title compound.Based on the above result, the oxidation of the carbon-carbon double bond of the side chain of xanthorrizol by permanganate ion (one equimolar) in acidic condition produced an α-hydroxy ketone compound as the main product (51.9%yield).However, the side products of the reaction have not been identified yet.The result reported earlier showed that the oxidation of carbon-carbon double bond in acidic condition afforded the cleavage products as the main product [12], for example, the oxidation of carbon-carbon double bond of the side chain of eugenol by permanganate ion (five equimolar) in acidic condition produced 3,4-dimethoxybenzyl carboxylic acid [16].The difference of the amount of permanganate ion used may cause different results in the oxidation reaction.* DB = Directly bonded proton-carbon, which are not seen in HMBC; α = due to a two-bond coupling ( 2 J CH ); β = due to a three-bond coupling ( 3 J CH ); γ = due to a four-bond coupling ( 4 J CH ).

ppm confirmed the formation of ketone (C=O) and C-O aliphatic groups
Based on the above result, the oxidation of the carbon-carbon double bond of the side chain of xanthorrizol by permanganate ion (one equimolar) in acidic condition produced an α-hydroxy ketone compound as the main product (51.9%yield).However, the side products of the reaction have not been identified yet.The result reported earlier showed that the oxidation of carbon-carbon double bond in acidic condition afforded the cleavage products as the main product [12], for example, the oxidation of carbon-carbon double bond of the side chain of eugenol by permanganate ion (five equimolar) in acidic condition produced 3,4-dimethoxybenzyl carboxylic acid [16].The difference of the amount of permanganate ion used may cause different results in the oxidation reaction.

General
Xanthorrhizol was supplied by Java Plant, Karanganyar, Indonesia.Potassium permanganate, hydrogen peroxide (Merck, Darmstadt, Germany), and solvents used were obtained commercially.A purity test was performed using thin layer chromatographic (TLC) method on silica gel 60 F254 plates (Merck).The infrared (IR) spectrum was recorded on a FTIR Spectrophotometer (Nicolet iS10, Thermo Fisher Scientific, Waltham, MA, USA); Nuclear Magnetic Resonance (NMR) spectra were measured on an NMR spectrometer (Agilent, Santa Clara, CA, USA) at 500 MHz for proton and 125 MHz for carbon using in CDCl 3 as solvent and tetramethylsilane (TMS) as internal standard.High-resolution Mass spectra (HRMS) was recorded on an LCT Premier XE-TOF Mass Spectrometer (Waters Corp., Milford, MA, USA) in positive electrospray ionization (ESI) mode.

Synthesis of the Title Compound 2
1-O-Acetyl-xanthorrhizol (1) was prepared by acetylation of xanthorrizol using phenol acetylation method reported earlier [10,11,13] with little modification.Furthermore, to a solution of the compound 1 (2.44 mmol, 635.3 mg) in a mixture of glacial acetic acid (5.45 mL), acetone (11 mL), and distilled water (4.3 mL), potassium permanganate crystal (2.7 mmol, 428 mg) was added slowly for 6 h while stirring in an ice bath (0-5 • C), then followed by additional stirring for 1 h.The reaction was monitored using TLC.Upon completion, the reaction solution was poured onto 12 mL of distilled water, and then, 2-3 drops of hydrogen peroxide solution were added to decolorize the reaction.The main product was extracted with dichloromethane and purified by column chromatography using a mixture of hexane

Table 1 .
HMBC Correlations for the title compound 2.