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1806 Table 1. Cyclobutane dimers identified from the alkaline hydrolyzate of corn stover ∗ Cyclobutane dimer Retention time (min) † m/z 245 Ratio m/z 219/249 Ratio m/z 249/308 www.soci.org D Dobberstein, M Bunzel Ratio m/z 293/308 m/z 661 CC ht 39.32 − – – – – CC hh 40.29 + – – – – CC hh 40.81 + – – – – CC ht 41.03 − – – – – CC ht 41.17 − – – – – CC hh 41.25 + – – – – CF ht 41.73 −
Ferulate oligomers from corn stover www.soci.org mV 2500 2000 1500 1000 500 S tri 7 0 0 5 10 15 20 25 30 35 40 min mV 250 200 150 100 50 0 mV 200 150 100 50 S tri 10 S tri 12 8-5-DFA 8-O-4/8-5-triFA 8-8(aryltetralin)/8-O-4-triFA 0 5 10 15 20 25 30 35 40 min X 1 X 2 X 4 8-5/5-5-triFA 120 100 80 60 40 20 0 1600 1200 0 0 0 5 10 15 20 25 30 35 40 min 0 5 10 15 20 25 30 35 40 min mV mV 800 400 0 mV 1600 1200 800 400 S tri 9 0 5 10 15 20 25 30 35 40 min S tri 11 S tri 13 5-5-DFA 0 5 10 15 20 25 30 35 40 min Figure 4. Semi-preparative RP-HPLC chromatograms (detection at 325 nm) showing the fractionation of the ‘trimeric’ Sephadex LH-20 fractions (Fig. 2). triFA: dehydrotriferulic acid. doublets indicate one unsubstituted trans-cinnamate side-chain, and two doublet-of-doublets indicate that only two of the three guaiacyl units are unsubstituted whereas the third one is linked in 5-position (absence of an 8 Hz coupling for the proton in 6-position). Comparison of the assigned proton data shows good agreement with literature data. 13 The molecular mass of the thirdcompoundisolatedfromS tri 7 was 578 indicating a ferulate trimer, too. Interpreting 1 Hand 13 C (from 2D HMQC experiment) NMR data this compound was unambiguously identified as 8- 8(aryltetralin)/8-O-4-dehydrodiferulic acid. Characteristic signals are for example two singlets at 7.33 and 7.61 ppm indicating two 8-linked ferulate units and two doublets at 4.58 and 3.93 ppm (2 Hz coupling) indicating the 8-8(aryltetralin) linkage. Absence of 16 Hz doublets indicated that none of the cinnamate side-chains is unsubstituted. Comparison of the NMR data with literature data 12 fully supported this assignment. Although two more compounds were isolated from S tri 7 (X1 and X2, Fig.4) an unambiguous identification of these compounds failed. Here, as also true for other fractions, solubility issues led to substance losses, reduced sensitivity in NMR, etc. Fraction S tri 9 contained 8-O-4/8-O-4-dehydrotriferulic acid (Fig. 5, III). The trimeric nature of this compound was confirmed by its molecular mass (578), and the assigned proton NMR data are in full agreement with published data. 12 Again, two singlets 7.31 and 7.34 ppm indicate two 8-O-4-linkages, confirmed by the absence of 16 Hz doublets and the fact that three doublet-of-doublets indicate that neither guaiacyl unit is further substituted. The second compound (X3) isolated from this fraction was characterized as a trimer but could not be unambiguously identified. The only compound which could be identified from the fractions S tri 10 and S tri 11 was the 5-5-coupled dehydrodiferulic acid. Identification of the compounds X4 and X5 failed. The compound isolated from S tri 12 was tentatively identified as 8-5/5- 5-dehydrotriferulic acid (Fig. 5, V). The chromatographic behavior of this compound during the fractionation as well as the mass spectrum and UV spectrum of this compound matches 8-5/5- J Sci Food Agric 2010; 90: 1802–1810 c○ 2010 Society of Chemical Industry www.interscience.wiley.com/jsfa 8-O-4/8-O-4-triFA 5-5/8-O-4-triFA X 3 X 5 1807
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