Natural Product Research
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solution was basified with ammonia and extracted with CHCl3. The CHCl3 extract
was evaporated to dryness which gave a mixture of crude alkaloids (4 g). The crude
alkaloidal fraction was chromatographed over SiO2 gel column eluting with a
mixture of CHCl3 and MeOH. The eluants collected from CHCl3–MeOH (25 : 1)
and (20 : 1) were purified separately by preparative TLC with solvents A and B,
which furnished the compounds xylopyrine-G (31 mg) (1) and xylopyrine-H (26 mg)
(2), respectively.
3.3.1. Xylopyrine-G (1)
Compound 1 crystallised from MeOH as colourless granules, m.p. 231–233ꢂC, Rf
25
0.25 (solvent A), 0.35 (solvent B), ½ꢂꢃD ¼ 230 (c, 0.32, CHCl3). It showed UV
(MeOH) ꢁmax, nm (log "): 210 (4.30), 250 (3.10); IR (KBr) ꢀmax cmꢀ1: 3410 (–NH),
2965–2860 (ꢀCH), 2790 (–OCH3), 1680, 1635 (sec. amide), 1610 (–C¼C–), 1240,
1040 (aryl ether); 125 MHz 13C-NMR (CDCl3 þ CD3OD) ꢃ: 121.4 (C-1), 125-5 (C-2),
169.7 (C-4), 53.9 (C-5), 171.7 (C-7), 55.2 (C-8), 80.8 (C-9), 155.8 (C-11), 121.5 (C-12),
121.5 (C-120), 130.4 (C-13), 130.4 (C-130), 133.3 (C-14), 38.9 (C-15), 135.6 (C-16),
127.8 (C-17), 127.8 (C-170), 128.7 (C-18), 128.7 (C-180), 126.1 (C-19), 134.6 (C-20),
129.0 (C-21), 129.0 (C-210), 130.2 (C-22), 130.2 (C-220), 127.5 (C-23), terminal amino
acid N-formylmonomethylleucine [172.4, 74.6, 25.6, 30.3, 19.2, 20.2, 171.8, 41.6];
HRMS, m/z: 582.2848 (C34H38N4O5), 427.1898 (C26H25N3O3), 412.1782
(C26H24N2O3), 371.1764 (C24H23N2O2), 308.1160 (C18H16N2O2), 278.1178
(C18H16NO2), 250.1233 (C17H16NO), 243.0770 (C13H11N2O3), 224.1078
(C15H14NO), 215.0836 (C12H11N2O2), 156.1026 (C8H14NO2), 135.0684 (C8H9NO),
131.0498 (C9H7O), 128.1078 (C7H14NO), 120.0814 (C8H10N), 102.0548 (C8H6) and
100.1128 (C6H14N).
3.3.2. Deformylation of xylopyrine-G (1)
Compound 1 (7 mg) was deformylated by treatment with 0.5 N HCl in MeOH at
room temperature for a period of 48 h. Usual work-up and crystallisation from
MeOH gave a colourless crystalline solid of compound 5 (4 mg) m.p. 185–187ꢂC;
MS, m/z: 554.2896 ([M]þ C33H38N4O4).
3.3.3. Methylation of compound 5
Compound 5 (8 mg) was treated with HCHO and NaBH4 by slow addition and
checking the reaction product by TLC. On usual work-up and crystallisation from
MeOH, it furnished the N-methylated product 6 as colourless granules (6 mg), m.p.
221–223ꢂC; MS, m/z: 568.3052 ([M]þ, C34H40N4O4). It was identical to crenatine-A
(Silva et al., 1974) (mmp, co-TLC and super-imposable IR) on comparison with
authentic sample.
3.3.4. Xylopyrine-H (2)
Compound 2, crystallised from MeOH as colourless granules, m.p. 216–218ꢂC, Rf
0.45 (solvent A), 0.62 (solvent B); [ꢂ]25 ¼ 280 (c, 0.28, CHCl3). It showed UV
(MeOH) ꢁmax, nm (log "): 215 (4.10), 248 (3.20); IR (KBr) ꢀmax, cmꢀ1: 3440 (–NH),
2955–2840 (–CH), 2785 (–OCH3), 1678, 1630 (sec. amide), 1610 (–C¼C–), 1240, 1040