Further Investigation Into Maple Syrup Yields Three New Lignans a New Phenylpropanoid and Twenty-Six Other Phytochemicals

摘要

Maple syrup is made by boiling the sap collected from certain maple (Acer) species. During this process, phytochemicals naturally present in tree sap are concentrated in maple syrup. We previously reported 23 phytochemicals from a butanol extract of Canadian maple syrup (MS-BuOH). Here we report the isolation and identification of 30 additional compounds (>1–30) from its ethyl acetate extract (MS-EtOAc) not previously reported from MS-BuOH. Of these, 4 compounds are new (>1–3, 18) and 20 compounds (>4–7, 10–12, 14–17, 19–20, 22–24, 26, 28–30) are being reported from maple syrup for the first time. The new compounds include 3 lignans and 1 phenylpropanoid: 5-(3″,4″-dimethoxyphenyl)-3-hydroxy-3-(4′-hydroxy-3′-methoxybenzyl)-4-hydroxymethyl-dihydrofuran-2-one (>1), (erythro, erythro)-1-[4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3,5-dimethoxyphenyl]-1,2,3-propanetriol (>2), (erythro, threo)-1-[4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3,5-dimethoxyphenyl]-1,2,3-propanetriol (>3) and 2,3-dihydroxy-1-(3,4-dihydroxyphenyl)-1-propanone (>18), respectively. In addition, 25 other phenolic compounds were isolated including (threo, erythro)-1-[4-[(2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3-methoxyphenyl]-1,2,3-propanetriol (>4), (threo, threo)-1-[4-[(2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-3-methoxyphenyl]-1,2,3-propanetriol (>5), threo-guaiacylglycerol-β-O-4′-dihydroconiferyl alcohol (>6), erythro-1-(4-hydroxy-3-methoxyphenyl)-2-[4-(3-hydroxypropyl)-2,6-dimethoxyphenoxy]-1,3-propanediol (>7), 2-[4-[2,3-dihydro-3-(hydroxymethyl)-5-(3-hydroxypropyl)-7-methoxy-2-benzofuranyl]-2,6-dimethoxyphenoxy]-1-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol (>8), acernikol (>9), leptolepisol D (>10), buddlenol E (>11), (1S,2R)-2-[2,6-dimethoxy-4-[(1S,3aR,4S,6aR)-tetrahydro-4-(4-hydroxy-3,5-dimethoxyphenyl)-1H,3H-furo[3,4-c]furan-1-yl]phenoxy]-1-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol (>12), syringaresinol (>13), isolariciresinol (>14), icariside E4 (>15), sakuraresinol (>16), 1,2-diguaiacyl-1,3-propanediol (>17), 2,3-dihydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (>19), 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)propan-1-one (>20), dihydroconiferyl alcohol (>21), 4-acetylcatechol (>22), 3′,4′,5′-trihydroxyacetophenone (>23), 3,4-dihydroxy-2-methylbenzaldehyde (>24), protocatechuic acid (>25), 4-(dimethoxymethyl)-pyrocatechol (>26), tyrosol (>27), isofraxidin (>28) and 4-hydroxycatechol (>29). One sesquiterpene, phaseic acid (>30), which is a known metabolite of the phytohormone, abscisic acid, was also isolated from MS-EtOAc. The antioxidant activities of MS-EtOAc (IC50 = 75.5 μg/mL), and the pure isolates (IC50 ca. 68–3000 μM) were comparable to vitamin C (IC50 = 40 μM) and the synthetic commercial antioxidant, butylated hydroxytoluene (IC50 = 3000 μM), in the diphenylpicrylhydrazyl radical scavenging assay. The current study advances scientific knowledge of maple syrup constituents and suggest that these diverse phytochemicals may impart potential health benefits to this natural sweetener.