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8.38 (d, J ¼ 8.2 Hz, 1H), 8.03 (d, J ¼ 8.2 Hz, 1H), 7.69–7.64 (m, award of the Swarnajayanti fellowship. D.G.V. thanks UGC, New
2H), 7.27 (t, J ¼ 6.7 Hz, 1H), 4.49 (d, J ¼ 9.5 Hz, 1H), 3.13 (dd, J ¼ Delhi for a fellowship.
16.6, 6.2 Hz, 1H), 2.58 (dd, J ¼ 16.6, 10.5 Hz, 1H), 2.43–2.31 (m,
1H), 1.27 (d, J ¼ 6.6 Hz, 3H); 13C NMR (CDCl3, 100 MHz): d
Notes and references
197.8, 187.5, 182.9, 162.3, 151.9, 137.3, 135.5, 135.3, 135.1,
134.2, 130.6, 129.7, 124.0, 119.9, 115.6, 73.5, 44.9, 38.2, 18.4;
HRMS (ESI): calcd. for C19H14O5Na (M + Na)+ m/z 345.0739,
found m/z 345.0752.
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Rubiginone A2 (3)
To a stirred solution of MOM ether 20 (50 mg, 0.13 mmol) in
MeOH (5 mL) at 0 ꢁC was added dropwise AcCl (0.1 mL, 10 equiv.)
and the reaction mixture was stirred for 12 h at room tempera-
ture. The reaction mixture was quenched with water, and
extracted with CH2Cl2 (3 ꢂ 10 mL). The organic layer was washed
with brine, dried over Na2SO4, and concentrated under vacuo.
The crude compound was puried by silica gel column chro-
matography (60% ethyl acetate in hexanes) to afford rubiginone
A2 3 (39.3 mg, 89%) as an orange solid; Rf ¼ 0.25 (1 : 1 ethyl
acetate/hexanes); mp ¼ (decomp) > 218 ꢁC; [a]D22 ¼ +62.0 (c 0.2,
CHCl3); IR (CHCl3): 3413, 3059, 3017, 2927, 2854, 1669, 1590,
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3267; (d) D. Mal and P. Pahari, Chem. Rev., 2007, 107,
1892–1918; (e) D. Mal and S. Dey, Tetrahedron, 2006, 62,
9589–9602.
1437, 1303, 1272, 1217, 1175, 1119, 1067, 755 cmꢀ1; H NMR
1
(CDCl3, 400 MHz): d 8.37 (d, J ¼ 8.2 Hz, 1H), 7.99 (d, J ¼ 8.2 Hz,
1H), 7.77 (d, J ¼ 7.2 Hz, 1H), 7.73 (t, J ¼ 8.0 Hz, 1H), 7.31 (d, J ¼ 8.0
Hz, 1H), 4.50 (d, J ¼ 9.3 Hz, 1H), 4.04 (s, 3H), 3.08 (dd, J ¼ 16.4, 5.6
Hz, 1H), 2.59–2.52 (m, 1H), 2.41–2.36 (m, 1H), 1.26 (d, J ¼ 6.4 Hz,
3H); 13C NMR (DMSO-d6, 100 MHz): d 198.1, 184.4, 181.0, 160.0,
153.0, 137.2, 136.6, 135.2, 134.1, 134.0, 131.8, 129.7, 120.2, 119.1,
118.9, 72.1, 56.9, 44.8, 38.2, 18.6; HRMS (ESI): calcd. for
4 P. W. Schindler, Biotech-Forum, 1989, 2, 142.
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C
20H16O5Na (M + Na)+ m/z 359.0895, found m/z 359.0900.
Rubiginone C2 (4)
To a solution of rubiginone A2 3 (50 mg, 0.15 mmol) dissolved in
CH2Cl2 (5 mL) were added isobutyryl chloride (23.8 mL, 0.22
mmol) and 4-dimethylaminopyridine (36.6 mg, 0.3 mmol) at
room temperature. The reaction mixture was stirred for 24 h,
hydrolyzed with water and extracted with CH2Cl2. Aer workup
and purication by silica gel column chromatography (30%
ethyl acetate in hexanes), rubiginone C2 4 was obtained as a
yellow solid (52 mg, 86%); Rf ¼ 0.5 (1 : 1 ethyl acetate/hexanes);
mp ¼ 215–218 ꢁC; [a]D22 ¼ ꢀ51.2 (c 0.5, CHCl3); IR (CHCl3): 2972,
2928, 2868, 1742, 1664, 1588, 1471, 1303, 1267, 1242, 1187,
1148, 1027, 759 cmꢀ1; 1H NMR (CDCl3, 400 MHz): d 8.35 (d, J ¼
8.2 Hz, 1H), 7.77 (dd, J ¼ 7.6, 1.2 Hz, 1H), 7.72 (t, J ¼ 8.2 Hz, 1H),
7.60 (d, J ¼ 8.2 Hz, 1H), 7.32 (dd, J ¼ 8.2, 1.2 Hz, 1H), 5.85 (d, J ¼
7.3 Hz, 1H), 4.04 (s, 3H), 3.2–3.14 (m, 1H), 2.72–2.59 (m, 3H),
1.24 (t, J ¼ 7.1 Hz, 6H), 1.13 (d, J ¼ 6.4 Hz, 3H); 13C NMR (CDCl3,
100 MHz): d 196.8, 184.1, 181.3, 176.5, 160.0, 146.0, 137.5, 136.1,
135.7, 134.9, 134.7, 131.5, 130.2, 120.6, 119.8, 117.5, 73.4, 56.6,
43.9, 35.2, 34.2, 19.1, 19,0, 18.1; HRMS (ESI): calcd. for C24H23O6
(M + H)+ m/z 407.1495, found m/z 407.1479.
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¨
7 K. Krohn, M. H. Sohrab and U. Florke, Tetrahedron:
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Acknowledgements
˜
9 (a) M. C. Carreno, A. Urbano and C. Di Vitta, Chem.–Eur. J.,
We thank DST, New Delhi and IIT Bombay for nancial support
˜
and the use of spectral facilities. K.P.K. thanks DST for the
2000, 6, 906–913; (b) M. C. Carreno, A. Urbano and C. Di
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