New isoflavan from Erythrina livingstoniana

New Isoflavan from Erythrina Livingstoniana Nayang A. Kgakatsi,a,c Runner R.T. Majinda,a Ishmael B. Masesanea, Mutshinyalo S. Nwamadi,b Taye B. Demissie,a Japheth O. Ombito,a Irene Gobed a Department of Chemistry, University of Botswana, Private Bag UB 0022, Gaborone, Botswana b Spectrum, University of Johannesburg, P.O Box 524, Auckland Park, 2006. Cnr Kingsway & University Roads, Auckland Park, Johannesburg, 2092, South Africa c d Boitekanelo College, P.O Box 203156, Old Naledi Kiosk, Gaborone, Botswana Department of Medical Laboratory Science, University of Botswana, Private Bag UB 0022, Gaborone, Botswana Correspondence: Nayang A. Kgakatsi; Email: kgakatsina@gmail.com; nkgakatsi@boitekanelo.ac.bw Abstract Chemical investigation of the root wood of Erythrina livingstoniana led to the isolation of one previously undescribed isoflavan (3S,3″R)-7-hydroxy-2′-methoxy-[3″-hydroxy-2″,2″dimethylpyrano (3′,4′)] isoflavan (1), together with eleven known compounds (2-12). The structure of compound 1 was elucidated on the basis of extensive spectroscopic and spectrometric analyses (1D and 2D-NMR and APCI-HRMS), with absolute configurations established by comparison of experimental and DFT calculated ECD data. The assignment of the absolute configurations of C-3 and C-3″ of compounds 2 and 3, respectively, were reported for the first time. Compounds 1 - 4 were evaluated for their antibacterial activities in vitro against E. coli ATCC 25922 and S. aureus ATCC 25923. Compound 1 exhibited moderate antibacterial activity with MIC value of 0.063 mg/mL against the clinically relevant risk-group 2 (RG-2) bacterium S. aureus. Contents 1. Tables Lists Table S1. 1H (500 MHz) and 13C NMR (125 MHz) spectroscopic data of compound 1 Table S2. 1H (500 MHz) and 13C NMR (125 MHz) spectroscopic data of compound 2 Table S3. 1H (500 MHz) and 13C NMR (125 MHz) spectroscopic data of compound 3 Table S4. Antibacterial activities of compounds 1 – 4 2. Figure Legends Figure S1. APCI-HRMS spectrum of compound 1 Figure S2. 1H NMR (500 MHz, Acetone-d6) spectrum of compound 1 Figure S3. 13C NMR (125 MHz, Acetone-d6) spectrum of compound 1 Figure S4. DEPT 135 NMR (125 MHz, Acetone-d6) spectrum of compound 1 Figure S5. 1H–1H COSY (500 MHz, Acetone-d6) spectrum of compound 1 Figure S6. HMQC spectrum of compound 1 in Acetone-d6 Figure S7. HMBC spectrum of compound 1 in Acetone-d6 Figure S8. NOESY spectrum of compound 1 in Acetone-d6 Figure S9. Key 1H–1H COSY, 1H–1H NOESY, and HMBC correlations of compound 1 Figure S10. Experimental and calculated electronic circular dichroism (ECD) spectra of compound 1 Figure S11. APCI-HRMS spectrum of compound 1 Figure S12. 1H NMR (500 MHz, Acetone-d6) spectrum of compound 2 Figure S13. 13C NMR (125 MHz, Acetone-d6) spectrum of compound 2 Figure S14. DEPT 135 NMR (125 MHz, Acetone-d6) spectrum of compound 2 Figure S15. 1H–1H COSY (500 MHz, Acetone-d6) spectrum of compound 2 Figure S16. HSQC spectrum of compound 2 in Acetone-d6 Figure S17. HMBC spectrum of compound 2 in Acetone-d6 Figure S18. Key 1H–1H COSY and HMBC correlations of compound 2 Figure S19. Experimental and calculated electronic circular dichroism (ECD) spectra of compound 2 Figure S20. 1H NMR (500 MHz, Acetone-d6) spectrum of compound 3 Figure S21. 13C NMR (125 MHz, Acetone-d6) spectrum of compound 3 Figure S22. DEPT 135 NMR (125 MHz, Acetone-d6) spectrum of compound 3 Figure S23. 1H–1H COSY (500 MHz, Acetone-d6) spectrum of compound 3 Figure S24. HSQC spectrum of compound 3 in Acetone-d6 Figure S25. HMBC spectrum of compound 3 in Acetone-d6 Figure S26. NOESY spectrum of compound 3 in Acetone-d6 Figure S27. Key 1H–1H COSY, 1H–1H NOESY, and HMBC correlations of compound 3 Figure S28. Experimental and calculated electronic circular dichroism (ECD) spectra of compound 3 1. Table Lists Table S1 1H and 13C NMR spectroscopic data of compound 1 Position 1 a δH, mult. J (Hz) δC b 2ax 3.94 m 70.2 2eq 4.17 dddd (8.8, 6.8, 3.6, 2.1) 3 3.47 tdd (11.0, 5.3, 3.6) 31.3 4 2.80 m 31.5 2.91 m 5 6.90 dd (8.3, 4.0) 130.1 6 6.39 ddd (8.3, 2.5, 1.4) 107.9 7 8 157.7 6.31 dd (2.5, 1.5) 102.8 9 155.1 10 113.4 1′ 125.4 2′ 156.9 3′ 113.6 4′ 153.1 5′ 6.57 d (8.5) 112.9 6′ 7.00 dd (8.5, 1.5) 125.5 1″ 2″ 76.6 3″ 3.81 m 68.4 4″ax 2.71 ddd (17.2, 9.8, 7.8) 26.7 4″eq 3.05 dt (16.9, 6.0) 5″ 1.26 s 19.6 6″ 1.36 s 25.2 2′-OCH3 3.79 s 61.2 a (500 MHz, acetone-d6); b(125 MHz, acetone-d6) Table S2 1H and 13C NMR spectroscopic data of compound 2 Position 2 a δH, mult. J (Hz) δC b 2ax 3.92 t (10.5) 2eq 4.17 ddd (10.4, 3.6, 2.1) 3 3.46 ddd (11.0, 5.3, 3.5) 31.4 4ax 2.80 ddd (15.7, 5.4, 2.1) 31.8 4eq 2.89 ddd (15.7, 11.3, 1.1) 5 6.90 d (8.2) 130.2 6 6.39 dd (8.2, 2.5) 107.9 7 8 70.4 157.7 6.32 dd (2.5) 102.8 9 155.1 10 113.5 1′ 125.5 2′ 157.4 3′ 121.7 4′ 155.0 5′ 6.69 d (8.4) 111.4 6′ 6.93 d (8.4) 125.0 1″ 3.40 m 23.2 2″ 5.31 tsep (7.3, 1.5) 123.6 3″ 130.1 4″ 1.68 d (1.5) 24.9 5″ 1.79 d (1.3) 17.1 3.75 s 61.4 6″ 2′-OCH3 a (500 MHz, acetone-d6); b(125 MHz, acetone-d6) Table S3: 1H and 13C NMR spectroscopic data of compound 3 Position 3 a δH, mult. J (Hz) δC b 2 5.44 dd (13.1, 2.9) 79.7 3ax 2.68 ddd (16.7, 2.9, 1.5) 43.8 3eq 3.06 *dd (16.7, 13.1) 4 189.6 5 7.74 d (8.7) 128.6 6 6.59 dd (8.7, 2.3) 110.3 7 8 163.6 6.43 d (2.3) 102.8 9 164.5 10 114.3 1′ 2′ 128.5 * 7.28 m 128.3 3′ 120.5 4′ 153.4 5′ 6.79 m 116.7 6′ 7.28 m 125.8 1″ 2″ 68.9 3″ 3.83 dd (9.5, 5.6) 77.2 4″eq 3.06 *dd (16.7, 13.1) 31.3 4″ax 2.78 ddd (16.7, 7.9, 2.9) 5″ 1.27 s 19.9 6″ 1.37 s 26.1 a (500 MHz, acetone-d6); b(125 MHz, acetone-d6); *Overlapping signals Table S4. Antibacterial activities of compounds 1 – 4 (MIC, mg/mL). Bacterial strains Tested compounds 1 2 3 4 Streptomycin S. aures ATCC 25923 0.063 0.125 0.125 0.125 0.005 E. coli ATCC 25922 1.000 1.000 1.000 1.000 0.001 2. Figure Lists Figure S1. APCI-HRMS spectrum of compound 1 Figure S2. 1H NMR (500 MHz, Acetone-d6) spectrum of compound 1 Figure S3. 13C NMR (125 MHz, Acetone-d6) spectrum of compound 1 Figure S4. DEPT 135 NMR (125 MHz, Acetone-d6) spectrum of compound 1 Figure S5. 1H–1H COSY (500 MHz, Acetone-d6) spectrum of compound 1 Figure S6. HMQC spectrum of compound 1 in Acetone-d6 Figure S7. HMBC spectrum of compound 1 in Acetone-d6 Figure S8. NOESY spectrum of compound 1 in Acetone-d6 Figure S9. Key 1H–1H COSY and HMBC correlations of compound 1 Figure S10. Experimental and calculated electronic circular dichroism (ECD) spectra of compound 1 Figure S11. APCI-HRMS spectrum of compound 2 Figure S12. 1H NMR (500 MHz, Acetone-d6) spectrum of compound 2 Figure S13. 13C NMR (125 MHz, Acetone-d6) spectrum of compound 2 Figure S14. DEPT 135 NMR (125 MHz, Acetone-d6) spectrum of compound 2 Figure S15. 1H–1H COSY (500 MHz, Acetone-d6) spectrum of compound 2 Figure S16. HSQC spectrum of compound 2 in Acetone-d6 Figure S17. HMBC spectrum of compound 2 in Acetone-d6 Figure S18. Key 1H–1H COSY and HMBC correlations of compound 2 Figure S19. Experimental and calculated electronic circular dichroism (ECD) spectra of compound 2 Figure S20. 1H NMR (500 MHz, Acetone-d6) spectrum of compound 3 Figure S21. 13C NMR (125 MHz, Acetone-d6) spectrum of compound 3 Figure S22. DEPT 135 NMR (125 MHz, Acetone-d6) spectrum of compound 3 Figure S23. 1H–1H COSY (500 MHz, Acetone-d6) spectrum of compound 3 Figure S24. HSQC spectrum of compound 3 in Acetone-d6 Figure S25. HMBC spectrum of compound 3 in Acetone-d6 Figure S26. NOESY spectrum of compound 3 in Acetone-d6 Figure S27. Key 1H–1H COSY, 1H-1H NOESY, and HMBC correlations of compound 3 Figure S28. Experimental and calculated electronic circular dichroism (ECD) spectra of compound 3