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Isocoumarin derivatives from the marine-derived fungus Phoma sp. 135
Tetrahedron Letters xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Isocoumarin derivatives from the marine-derived fungus Phoma sp. 135 Mahmoud F. Elsebai a,b,⇑, Hazem A. Ghabbour c,d a
Department of Pharmacognosy, Faculty of Pharmacy, Mansoura University, Egypt Department of Chemistry, University of Oulu, PO Box 3000, FIN-90014 Oulu, Finland c Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia d Department of Medicinal Chemistry, Faculty of Pharmacy, Mansoura University, Mansoura 35516, Egypt b
a r t i c l e
i n f o
Article history: Received 23 August 2015 Revised 23 October 2015 Accepted 3 December 2015 Available online xxxx Keywords: Chlorinated isocoumarin Phoma sp. X-ray analysis Marine natural products Structure elucidation Absolute stereochemistry
a b s t r a c t The dihydro-isocoumarin derivatives 1–2 were isolated from the marine-derived fungus Phoma sp. 135. Structural elucidation was achieved through extensive spectroscopic evaluation including 1D- and 2DNMR, accurate mass measurements, and single crystal X-ray diffraction analysis. We report herein the structure and absolute configuration of the known compound 1 using X-ray diffraction, and the structural elucidation of the new dihydro-isocoumarin derivative 2. Ó 2015 Elsevier Ltd. All rights reserved.
Introduction
Results and discussion
The marine-derived fungi are a prolific source of natural products.1 Dihydro-isocoumarins are a small group of interesting secondary polyketides of limited but diversified distribution that are produced by plants, insects, liverworts, bacteria, fungi (including endophytic, entomogenous, soil, and marine algicolous fungi), and sponges.2 They exhibit important biological and pharmacological properties such as anticancer, antimicrobial, plant growth inhibition, antimalarial, insecticidal, antioxidant, and antiallergic activities.3 They have also been shown to be involved in the biosynthetic pathways of several metabolites, and enrichment studies using singly and doubly labelled 13C-acetate have suggested a polyketide origin.4,5 Herein, we report the isolation and characterization of compounds 1–2 from the marine-derived fungus Phoma sp. 135, including the single crystal X-ray crystallographic data of compound 1 for the first time, and the new mellein derivative 2. Compound 1 was produced in large amounts, and thus it could be used as a chemotaxonomic marker for this fungus.
The marine-derived fungus Phoma sp. 135 was isolated from the sponge Ectyplasia perox collected in Dominica, Lauro Club Reef. Upon cultivation in a BMS (biomalt agar medium) medium supplemented with sea salt, Phoma sp. 135 produced halogenated dihydro-isocoumarin derivatives 1 and 2. These isolated isocoumarins are closely related derivatives of mellein (8-OH-dihydro-isocoumarin) differing only in the halogenation and substitution pattern and showed characteristic similarities in the IR, UV and NMR spectra. Subfraction 9 of the EtOAc extract of the culture filtrate as well as the mycelium of Phoma sp. 135 was subjected to RP-HPLC separation giving two crystalline compounds 1 and 2 (Fig. 1). Compound 1 showed a molecular formula of C11H11ClO4 on the basis of accurate mass measurement (HRESI+MS m/z had double peaks at 243.0406 and 245.0394 [M+H]+), and the number of signals in both the 1H and 13C NMR spectra (ESI, Figs. S1 and S2). The structure of compound 1 was confirmed by single crystal X-ray crystallographic measurements (Fig. 2) which was grown from a 1:1 chloroform/methanol mixture. The absolute configuration of the chiral centre at C-2 was determined as (R) based on the presence of the heavy chloride atom Cl-9. A perspective drawing of the molecular structure is shown in Figure 2 and the bond lengths and angles are given in Table S4 (ESI). The present
⇑ Corresponding author. Tel.: +20 50 2246253; fax: +20 50 2247496. E-mail address: [email protected] (M.F. Elsebai). http://dx.doi.org/10.1016/j.tetlet.2015.12.024 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Elsebai, M. F.; Ghabbour, H. A. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.12.024
2
M. F. Elsebai, H. A. Ghabbour / Tetrahedron Letters xxx (2015) xxx–xxx
Figure 1. Structures of the dihydro-isocoumarin derivatives isolated from Phoma sp. 135.
Figure 2. ORTEP diagram of compound 1 drawn at 50% ellipsoids for non-hydrogen atoms.
compound is identical to the known compound (3R)-6-methoxy-7chloromellein.6,7 Complete data for the X-ray diffraction analyses are presented in Tables S3–S8 (ESI). Compound 2 showed a molecular formula of C11H11ClO5 on the basis of accurate mass measurement (HRESI+MS m/z had double peaks at 281.0187 and 283.0159 [M+Na]+), and the number of signals in both the 1H and 13C NMR spectra (ESI, Figs. S9 and S10). The 1H NMR spectrum (Table 1 and ESI, Fig. S9) of 2 gave rise to a signal for one highly downfield shifted phenolic group at dH 11.75 for OH-10 which was strongly chelated with the C-1 carbonyl group at dC 169.3 (IR 1718 and 3465 cm 1) confirming hydrogen bond chelation. The 1H NMR spectrum also showed a characteristic singlet aromatic proton (dH 6.94 for H-6) indicating the presence of a penta-substituted benzene ring. The 13C-spectrum (Table 1 and ESI, Fig. S10) had a pattern of chemical shifts for this penta-substituted aryl system which were similar to the structural moiety of compound 1 indicating that both compounds possessed the same
Table 1 NMR spectroscopic data of compound 2 No.
dC (type)
1 2 3 4 5 6 7 8 9 10 11 OH-10
169.3 (C) 80.6 (CH) 18.1 (CH3) 69.0 (CH) 144.4 (C) 101.2 (CH) 159.3 (C) 57.1 (CH3) 102.2 (C) 162.2 (C) 108.5 (C)
dH, mult., (J in Hz)
1
H–1H COSY
1
H–13C HMBC
1
H–1H NOESY
4.57, m 1.49, d (6.29) 4.68, d (8.71)
3, 4 2 2
1, 3, 4, 5 2, 4 3, 5, 6, 11
3 2
6.94, s
1, 4, 9, 11
8
4.01, s
6, 7, 9
6
11.75, s
9, 10, 11
substituted aryl system (Fig. 1). Thus, carbons 5, 6, 7, 9, 10 and 11 constitute the penta-substituted aryl system having methoxy, hydroxy and chloride functional groups. This was further confirmed by the HMBC correlations of the H-6 aromatic proton to C-9 and C-11, the HMBC correlations of OH-10 to C-9, C-10 and C-11, and the HMBC correlations of MeO-8 to C-6, C-7 and C-9 (Fig. 3). The presence of the Cl atom was confirmed from the characteristic double peaks (peak heights were in the ratio of 3:1) in the mass spectrum of the two main natural isotopes of Cl at 281.0187 and 283.0159 [M+Na]+ and the attachment to C-9 was based on its chemical shift at dC 102.2 in the 13C-spectrum which was close to the respective carbon in compound 1 C-9 (dC 104.0). The carbonyl, CO-1, had a hydrogen bond chelation with the phenolic OH-10 due to the strongly downfield shift of OH-10 (the same H-bond chelation in 1 as shown by the single crystal X-ray diffraction analysis of 1, Fig. 2). Based on the aforementioned data, the substitution pattern of mellein halogenation is through chlorination by Phoma sp. as in compounds 1 and 2, while it was through bromination by the discomycete Lachnum palmae.8 The 1H NMR spectrum also showed a doublet resonance signal at dH 4.68 for H-4 which had a COSY correlation with the multiplet resonance signal at dH 4.57 for H-2, and a doublet for the secondary methyl group at dH 1.49 for CH3-3. The protons, H-1, H-2 and H-3, constituted one spin system due to the COSY correlations of the multiplet methine proton H-2 with H3-3 and H-4. Both methines, CH-2 and CH-4, were downfield shifted indicating their oxygenation pattern, and hence CH-2 and CH-4 constitute a benzopyran ring with the aryl moiety. This was confirmed from the mutual COSY and HMBC correlations connecting the penta-substituted benzene nucleus with the pyran ring (Figs. 1 and 3). The mass spectrum difference between compounds 1 and 2 (DM = 16) showed one additional oxygen atom for 2 which was located at C-4 dC 69.0 due to its chemical shift indicating an oxygenated carbon. For the configuration of compounds 1–2, the single crystal X-ray diffraction analysis showed that compound 1 has the (R) configuration of the chiral centre at C-2 based on the presence of a heavy chloride atom at C-9. The absolute configuration (R) of dihydro-isocoumarins is the commonly occurring enantiomer and is usually produced in substantial amounts facilitating their use for chemotaxonomic purposes.6 For compound 2, we assume the (R) configuration at the stereogenic centre at C-2 due to it having the same biogenetic origin as compound 1. The downfield signal for H-4 at dH 4.68 showed a coupling constant of 8.71 Hz indicating a
Figure 3. Key HMBC correlations of compound 2.
Please cite this article in press as: Elsebai, M. F.; Ghabbour, H. A. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.12.024
M. F. Elsebai, H. A. Ghabbour / Tetrahedron Letters xxx (2015) xxx–xxx
trans-relationship with the vicinal H-2 indicating the (S) configuration at C-4. X-ray diffraction structure determination for compound 1: Crystallographic data for compound 1 reported in this Letter have been deposited with the Cambridge Crystallographic Data Centre. Copies of the data can be obtained, free of charge, on application to the Director, CCDC 1432640, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 (0)1223 336033 or e-mail: [email protected]), www.ccdc.cam.ac.uk/data_request/cif. Crystal data: Photographic investigation showed the crystals were monoclinic, with space group P21, and accurate lattice constants of a = 4.8458 (4) Å, b = 5.7742 (5) Å, c = 18.6415 (14) Å, a = 90.00°, b = 95.901 (6)°, c = 90.00° and Z = 2; crystal size (mm) 0.57 0.21 0.08; Volume 518.84 (7) Å3; density (calcd) 1.533 Mg/m 3; absorption coefficient 3.26 mm 1; F(0 0 0) = 252; T = 100 (2) K. Theta range for data collection 2.40–66.2°; reflections collected/unique 1742/1421 [Rint = 0.059]; completeness to theta 33.1° 98.4%; multi-scan absorption correction; full-matrix leastsquares on F2; final R indices [I > 2r(I)] R1 = 0.084, wR2 = 0.255; largest diff. peak and hole 0.54 and 0.98 e Å 3. The structure was solved by a direct method and refined by a full-matrix leastsquare method. The absolute configuration was determined on the basis of the Flack parameter 0.03 (4). The metabolite was identified as (3R)-6-methoxy-7-chloromellein. Compound 2: White crystalline compound (6.2 mg; isolated amount 0.6 mg L 1); mp 73–74 °C; [a]D 75.0 ± 1 (c 0.26, MeOH); UV (MeOH) kmax (log e): 272 (4.50), 300 (3.98); 320 (4.20) nm; IR mmax (ATR): 3562, 3465, 3355, 2920, 1800, 1718, 1650, 1388, 1378, 1290, 1218, 1170, 1136, 1126, 1045 cm 1; 1H NMR and 13C NMR data, see Table 1; (+)-HRESIMS: found: 281.0187 [M+Na]+ and 283.0159 [M+Na]+, calcd for C11H11ClO5, 281.0193 [M+Na]+ and 283.0163 [M+Na]+.
3
Acknowledgments The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding of this research through the Research Group Project No. (RGP-1436-038). The author is grateful to Dr. S. Mattila (Department of Chemistry, University of Oulu, Finland) for measuring the HRESIMS. Supplementary data Supplementary data (1H and 13C NMR spectra for compounds 1– 2, X-ray diffraction analyses data of compound 1 and experimental procedures) associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2015.12.024. References and notes 1. Elsebai, M. F.; Saleem, M.; Tejesvi, M. V.; Kajula, M.; Mattila, S.; Mehiri, M.; Turpeinen, A. Nat. Prod. Rep. 2014, 31, 628–645. 2. Engelmeier, D.; Hadacek, F.; Hofer, O.; Lutz-Kutschera, G.; Nagl, M.; Wurz, G.; Greger, H. J. Nat. Prod. 2004, 67, 19–25. 3. Braca, A.; Bader, A.; De Tommasi, N. In Stud. Nat. Prod. Chem.; Atta-Ur Rahman, Ed.; Dipartimento di Scienze Farmaceutiche, Universita di Pisa: Pisa, Italy, 2012; pp 191–215. 4. Henderson, G. B.; Hill, R. A. J. Chem. Soc., Perkin Trans. 1 1982, 3037–3039. 5. Holker, J. S. E.; Young, K. J. Chem. Soc., Chem. Commun. 1975, 525–526. 6. Krohn, K.; Bahramsari, R.; Flsrke, U.; Ludewig, K.; Kliche, C.; Michel, A.; Aust, H. R.; Draeger, S.; Schulz, B.; Antus, S. Phytochemistry 1997, 45, 313–320. 7. Compound 1: White crystalline needles (85 mg; isolated amount was 8.5 mg L 1); [a]D 48.0 ± 2 (c 0.06, MeOH); 1H and 13C NMR (CDCl3, 25 °C, TMS): dH/C 171.0 (CO-1), 4.66/77.2 (CH-2), 1.47/22.1 (CH-3), 2.87/36.1 (CH2-4), 140.5 (C-5), 6.28/103.4 (CH-6), 162.2 (C-7), 3.90/57.9 (CH3O-8), 104.1 (C-9), 160.3 (C-10), 109.3 (C-11); (+)HRESIMS m/z = found 243.0406 and 245.0394, calcd for C11H11ClO4, 243.0424 and 245.0395 [M+H]+. 8. Shigemori, H.; Tanabe, Y.; Matsumoto, T.; Hosoya, T.; Sato, H. Heterocycles 2013, 87, 1481.
Please cite this article in press as: Elsebai, M. F.; Ghabbour, H. A. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.12.024
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Isocoumarin derivatives from the marine-derived fungus Phoma sp. 135 Mahmoud F. Elsebai a,b,⇑, Hazem A. Ghabbour c,d a
Department of Pharmacognosy, Faculty of Pharmacy, Mansoura University, Egypt Department of Chemistry, University of Oulu, PO Box 3000, FIN-90014 Oulu, Finland c Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia d Department of Medicinal Chemistry, Faculty of Pharmacy, Mansoura University, Mansoura 35516, Egypt b
a r t i c l e
i n f o
Article history: Received 23 August 2015 Revised 23 October 2015 Accepted 3 December 2015 Available online xxxx Keywords: Chlorinated isocoumarin Phoma sp. X-ray analysis Marine natural products Structure elucidation Absolute stereochemistry
a b s t r a c t The dihydro-isocoumarin derivatives 1–2 were isolated from the marine-derived fungus Phoma sp. 135. Structural elucidation was achieved through extensive spectroscopic evaluation including 1D- and 2DNMR, accurate mass measurements, and single crystal X-ray diffraction analysis. We report herein the structure and absolute configuration of the known compound 1 using X-ray diffraction, and the structural elucidation of the new dihydro-isocoumarin derivative 2. Ó 2015 Elsevier Ltd. All rights reserved.
Introduction
Results and discussion
The marine-derived fungi are a prolific source of natural products.1 Dihydro-isocoumarins are a small group of interesting secondary polyketides of limited but diversified distribution that are produced by plants, insects, liverworts, bacteria, fungi (including endophytic, entomogenous, soil, and marine algicolous fungi), and sponges.2 They exhibit important biological and pharmacological properties such as anticancer, antimicrobial, plant growth inhibition, antimalarial, insecticidal, antioxidant, and antiallergic activities.3 They have also been shown to be involved in the biosynthetic pathways of several metabolites, and enrichment studies using singly and doubly labelled 13C-acetate have suggested a polyketide origin.4,5 Herein, we report the isolation and characterization of compounds 1–2 from the marine-derived fungus Phoma sp. 135, including the single crystal X-ray crystallographic data of compound 1 for the first time, and the new mellein derivative 2. Compound 1 was produced in large amounts, and thus it could be used as a chemotaxonomic marker for this fungus.
The marine-derived fungus Phoma sp. 135 was isolated from the sponge Ectyplasia perox collected in Dominica, Lauro Club Reef. Upon cultivation in a BMS (biomalt agar medium) medium supplemented with sea salt, Phoma sp. 135 produced halogenated dihydro-isocoumarin derivatives 1 and 2. These isolated isocoumarins are closely related derivatives of mellein (8-OH-dihydro-isocoumarin) differing only in the halogenation and substitution pattern and showed characteristic similarities in the IR, UV and NMR spectra. Subfraction 9 of the EtOAc extract of the culture filtrate as well as the mycelium of Phoma sp. 135 was subjected to RP-HPLC separation giving two crystalline compounds 1 and 2 (Fig. 1). Compound 1 showed a molecular formula of C11H11ClO4 on the basis of accurate mass measurement (HRESI+MS m/z had double peaks at 243.0406 and 245.0394 [M+H]+), and the number of signals in both the 1H and 13C NMR spectra (ESI, Figs. S1 and S2). The structure of compound 1 was confirmed by single crystal X-ray crystallographic measurements (Fig. 2) which was grown from a 1:1 chloroform/methanol mixture. The absolute configuration of the chiral centre at C-2 was determined as (R) based on the presence of the heavy chloride atom Cl-9. A perspective drawing of the molecular structure is shown in Figure 2 and the bond lengths and angles are given in Table S4 (ESI). The present
⇑ Corresponding author. Tel.: +20 50 2246253; fax: +20 50 2247496. E-mail address: [email protected] (M.F. Elsebai). http://dx.doi.org/10.1016/j.tetlet.2015.12.024 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Elsebai, M. F.; Ghabbour, H. A. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.12.024
2
M. F. Elsebai, H. A. Ghabbour / Tetrahedron Letters xxx (2015) xxx–xxx
Figure 1. Structures of the dihydro-isocoumarin derivatives isolated from Phoma sp. 135.
Figure 2. ORTEP diagram of compound 1 drawn at 50% ellipsoids for non-hydrogen atoms.
compound is identical to the known compound (3R)-6-methoxy-7chloromellein.6,7 Complete data for the X-ray diffraction analyses are presented in Tables S3–S8 (ESI). Compound 2 showed a molecular formula of C11H11ClO5 on the basis of accurate mass measurement (HRESI+MS m/z had double peaks at 281.0187 and 283.0159 [M+Na]+), and the number of signals in both the 1H and 13C NMR spectra (ESI, Figs. S9 and S10). The 1H NMR spectrum (Table 1 and ESI, Fig. S9) of 2 gave rise to a signal for one highly downfield shifted phenolic group at dH 11.75 for OH-10 which was strongly chelated with the C-1 carbonyl group at dC 169.3 (IR 1718 and 3465 cm 1) confirming hydrogen bond chelation. The 1H NMR spectrum also showed a characteristic singlet aromatic proton (dH 6.94 for H-6) indicating the presence of a penta-substituted benzene ring. The 13C-spectrum (Table 1 and ESI, Fig. S10) had a pattern of chemical shifts for this penta-substituted aryl system which were similar to the structural moiety of compound 1 indicating that both compounds possessed the same
Table 1 NMR spectroscopic data of compound 2 No.
dC (type)
1 2 3 4 5 6 7 8 9 10 11 OH-10
169.3 (C) 80.6 (CH) 18.1 (CH3) 69.0 (CH) 144.4 (C) 101.2 (CH) 159.3 (C) 57.1 (CH3) 102.2 (C) 162.2 (C) 108.5 (C)
dH, mult., (J in Hz)
1
H–1H COSY
1
H–13C HMBC
1
H–1H NOESY
4.57, m 1.49, d (6.29) 4.68, d (8.71)
3, 4 2 2
1, 3, 4, 5 2, 4 3, 5, 6, 11
3 2
6.94, s
1, 4, 9, 11
8
4.01, s
6, 7, 9
6
11.75, s
9, 10, 11
substituted aryl system (Fig. 1). Thus, carbons 5, 6, 7, 9, 10 and 11 constitute the penta-substituted aryl system having methoxy, hydroxy and chloride functional groups. This was further confirmed by the HMBC correlations of the H-6 aromatic proton to C-9 and C-11, the HMBC correlations of OH-10 to C-9, C-10 and C-11, and the HMBC correlations of MeO-8 to C-6, C-7 and C-9 (Fig. 3). The presence of the Cl atom was confirmed from the characteristic double peaks (peak heights were in the ratio of 3:1) in the mass spectrum of the two main natural isotopes of Cl at 281.0187 and 283.0159 [M+Na]+ and the attachment to C-9 was based on its chemical shift at dC 102.2 in the 13C-spectrum which was close to the respective carbon in compound 1 C-9 (dC 104.0). The carbonyl, CO-1, had a hydrogen bond chelation with the phenolic OH-10 due to the strongly downfield shift of OH-10 (the same H-bond chelation in 1 as shown by the single crystal X-ray diffraction analysis of 1, Fig. 2). Based on the aforementioned data, the substitution pattern of mellein halogenation is through chlorination by Phoma sp. as in compounds 1 and 2, while it was through bromination by the discomycete Lachnum palmae.8 The 1H NMR spectrum also showed a doublet resonance signal at dH 4.68 for H-4 which had a COSY correlation with the multiplet resonance signal at dH 4.57 for H-2, and a doublet for the secondary methyl group at dH 1.49 for CH3-3. The protons, H-1, H-2 and H-3, constituted one spin system due to the COSY correlations of the multiplet methine proton H-2 with H3-3 and H-4. Both methines, CH-2 and CH-4, were downfield shifted indicating their oxygenation pattern, and hence CH-2 and CH-4 constitute a benzopyran ring with the aryl moiety. This was confirmed from the mutual COSY and HMBC correlations connecting the penta-substituted benzene nucleus with the pyran ring (Figs. 1 and 3). The mass spectrum difference between compounds 1 and 2 (DM = 16) showed one additional oxygen atom for 2 which was located at C-4 dC 69.0 due to its chemical shift indicating an oxygenated carbon. For the configuration of compounds 1–2, the single crystal X-ray diffraction analysis showed that compound 1 has the (R) configuration of the chiral centre at C-2 based on the presence of a heavy chloride atom at C-9. The absolute configuration (R) of dihydro-isocoumarins is the commonly occurring enantiomer and is usually produced in substantial amounts facilitating their use for chemotaxonomic purposes.6 For compound 2, we assume the (R) configuration at the stereogenic centre at C-2 due to it having the same biogenetic origin as compound 1. The downfield signal for H-4 at dH 4.68 showed a coupling constant of 8.71 Hz indicating a
Figure 3. Key HMBC correlations of compound 2.
Please cite this article in press as: Elsebai, M. F.; Ghabbour, H. A. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.12.024
M. F. Elsebai, H. A. Ghabbour / Tetrahedron Letters xxx (2015) xxx–xxx
trans-relationship with the vicinal H-2 indicating the (S) configuration at C-4. X-ray diffraction structure determination for compound 1: Crystallographic data for compound 1 reported in this Letter have been deposited with the Cambridge Crystallographic Data Centre. Copies of the data can be obtained, free of charge, on application to the Director, CCDC 1432640, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 (0)1223 336033 or e-mail: [email protected]), www.ccdc.cam.ac.uk/data_request/cif. Crystal data: Photographic investigation showed the crystals were monoclinic, with space group P21, and accurate lattice constants of a = 4.8458 (4) Å, b = 5.7742 (5) Å, c = 18.6415 (14) Å, a = 90.00°, b = 95.901 (6)°, c = 90.00° and Z = 2; crystal size (mm) 0.57 0.21 0.08; Volume 518.84 (7) Å3; density (calcd) 1.533 Mg/m 3; absorption coefficient 3.26 mm 1; F(0 0 0) = 252; T = 100 (2) K. Theta range for data collection 2.40–66.2°; reflections collected/unique 1742/1421 [Rint = 0.059]; completeness to theta 33.1° 98.4%; multi-scan absorption correction; full-matrix leastsquares on F2; final R indices [I > 2r(I)] R1 = 0.084, wR2 = 0.255; largest diff. peak and hole 0.54 and 0.98 e Å 3. The structure was solved by a direct method and refined by a full-matrix leastsquare method. The absolute configuration was determined on the basis of the Flack parameter 0.03 (4). The metabolite was identified as (3R)-6-methoxy-7-chloromellein. Compound 2: White crystalline compound (6.2 mg; isolated amount 0.6 mg L 1); mp 73–74 °C; [a]D 75.0 ± 1 (c 0.26, MeOH); UV (MeOH) kmax (log e): 272 (4.50), 300 (3.98); 320 (4.20) nm; IR mmax (ATR): 3562, 3465, 3355, 2920, 1800, 1718, 1650, 1388, 1378, 1290, 1218, 1170, 1136, 1126, 1045 cm 1; 1H NMR and 13C NMR data, see Table 1; (+)-HRESIMS: found: 281.0187 [M+Na]+ and 283.0159 [M+Na]+, calcd for C11H11ClO5, 281.0193 [M+Na]+ and 283.0163 [M+Na]+.
3
Acknowledgments The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding of this research through the Research Group Project No. (RGP-1436-038). The author is grateful to Dr. S. Mattila (Department of Chemistry, University of Oulu, Finland) for measuring the HRESIMS. Supplementary data Supplementary data (1H and 13C NMR spectra for compounds 1– 2, X-ray diffraction analyses data of compound 1 and experimental procedures) associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2015.12.024. References and notes 1. Elsebai, M. F.; Saleem, M.; Tejesvi, M. V.; Kajula, M.; Mattila, S.; Mehiri, M.; Turpeinen, A. Nat. Prod. Rep. 2014, 31, 628–645. 2. Engelmeier, D.; Hadacek, F.; Hofer, O.; Lutz-Kutschera, G.; Nagl, M.; Wurz, G.; Greger, H. J. Nat. Prod. 2004, 67, 19–25. 3. Braca, A.; Bader, A.; De Tommasi, N. In Stud. Nat. Prod. Chem.; Atta-Ur Rahman, Ed.; Dipartimento di Scienze Farmaceutiche, Universita di Pisa: Pisa, Italy, 2012; pp 191–215. 4. Henderson, G. B.; Hill, R. A. J. Chem. Soc., Perkin Trans. 1 1982, 3037–3039. 5. Holker, J. S. E.; Young, K. J. Chem. Soc., Chem. Commun. 1975, 525–526. 6. Krohn, K.; Bahramsari, R.; Flsrke, U.; Ludewig, K.; Kliche, C.; Michel, A.; Aust, H. R.; Draeger, S.; Schulz, B.; Antus, S. Phytochemistry 1997, 45, 313–320. 7. Compound 1: White crystalline needles (85 mg; isolated amount was 8.5 mg L 1); [a]D 48.0 ± 2 (c 0.06, MeOH); 1H and 13C NMR (CDCl3, 25 °C, TMS): dH/C 171.0 (CO-1), 4.66/77.2 (CH-2), 1.47/22.1 (CH-3), 2.87/36.1 (CH2-4), 140.5 (C-5), 6.28/103.4 (CH-6), 162.2 (C-7), 3.90/57.9 (CH3O-8), 104.1 (C-9), 160.3 (C-10), 109.3 (C-11); (+)HRESIMS m/z = found 243.0406 and 245.0394, calcd for C11H11ClO4, 243.0424 and 245.0395 [M+H]+. 8. Shigemori, H.; Tanabe, Y.; Matsumoto, T.; Hosoya, T.; Sato, H. Heterocycles 2013, 87, 1481.
Please cite this article in press as: Elsebai, M. F.; Ghabbour, H. A. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.12.024