A. W. W. van Wyk et al. / Tetrahedron 61 (2005) 8493–8498
8497
standard pulse sequences. Chemical shifts are reported in
ppm, referenced to residual solvent resonances (CDCl3 dH
7.25, dC 77.0), and coupling constants are reported in Hz.
HRFABMS data were obtained on a JEOL SX102
spectrometer.
yellow oil (150 mg) that after normal phase HPLC (9:1
hexane/EtOAc) gave 2 (65 mg, 45%), 3 (14 mg, 9%), 7
(2 mg, 1%)13 and 8 (3 mg, 2%).13
4.4.1. 9a-Cyano-15,16-epoxy-7b-hydroxylabda-13(16),
14-dien-6-one (2). White amorphous solid; [a]DC53
(c 0.80, CHCl3), IR nmax 3469, 2980, 2874, 2228, 1715,
4.1. Isolation of hispanolone (1) from B. africana
1
1464, 1366, 1046, 874, 780 cmK1; H and 13C NMR data
Aerial parts of B. africana were collected 40 kms south
west of Grahamstown, South Africa in November 2003.
Air-dried leaves (250 g) were steeped in Me2CO (3.5 L) for
3 days, the Me2CO solution concentrated in vacuo,
decolourised with activated charcoal (20 g), adsorbed onto
HP-20 beads and eluted sequentially with aliquots (1.5 L) of
40 and 60% aqueous acetone. The fraction eluted with 60%
aqueous acetone was diluted with H2O (1.5 L) and allowed
to stand at 4 8C for 4 days to afford 1 (3.82 g, 1.52%) as
white crystalline plates (acetone/water); mp 133–135 8C,
lit.3 142–144 8C; [a]D32K18.8 (c 6.35, CHCl3), lit.3 K17.6;
IR, 1H and 13C NMR data consistent with published
values.3,8
see Table 2; EIMS m/z (rel. int.) 343 [MC] (6), 326 (17), 314
(5), 262 (8), 182 (21), 139 (29), 121 (25), 95 (100), 67 (46);
HRFABMS m/z 344.2226 (calcd for C21H30NO3 [(MC
H)C], 344.2226).
4.4.2. 9a-Cyano-15,16-epoxy-7-hydroxylabda-7,13(16),
14-trien-6-one (3). White needles (from benzene/hexane);
mp 138–139 8C; [a]DK44 (c 0.73, CHCl3); IR nmax 3397
(br), 2927, 2863, 2351, 2222, 1683, 1456, 1386, 1122, 876,
1
792 cmK1; H and 13C NMR data see Table 2; EIMS m/z
(rel. int.) 341 [MC] (13), 326 (100), 243 (12), 167 (15), 95
(17), 81 (19), 67 (15), 55 (11); HRFABMS m/z 341.1992
(calcd for C21H27NO3 [(M)C], 341.1990).
4.2. Dehydration of 1 and a-acetoxylation of hispanone
(5)
4.5. LAH reduction of 2
A solution of LiAlH4 (3.6 mg, 0.038 mmol) and 2 (13 mg,
0.03 mmol) in dry THF (4 mL) was refluxed (5 h), cooled
and acidified. The solvent was removed in vacuo and the
residue taken up in EtOAc (5 mL), washed with H2O (3!
2 mL), dried (anhydrous MgSO4) and concentrated to yield
a yellowish oil (17 mg). Subsequent purification with
normal phase HPLC (4:1 hexane/EtOAc) yielded 4
(13 mg, 0.038 mmol, 98%).
The procedures for the dehydration of 1 to give 5 and the
subsequent a-acetoxylation of 5 to give the epimeric
acetates 9 and 10 have been previously reported.13
4.3. Saponification of 9 and 10
A solution of 9 (163 mg, 0.46 mmol) in EtOH (30 mL) and
1.5 M KOH (5.0 mL) was heated at 70 8C for 1 h. The
reaction mixture was cooled, 1.0 M HCl (10.0 mL) added
and the EtOH removed in vacuo to give a cloudy suspension
that was extracted with CH2Cl2 (3!15 mL). The organic
phases were combined, washed with 5% aqueous NaHCO3
(10 mL), dried (anhydrous MgSO4) and concentrated to
give a yellow oil (106 mg). Column chromatography
(4:1 hexane/EtOAc) and normal phase semi-preparative
HPLC of the oil (19:1 hexane/EtOAc) gave 7 (7 mg, 4%),13
(8, 45 mg, 30%)13 and 11 (38 mg, 26%). The saponification
procedure was repeated on 10 (58 mg, 0.16 mmol) and the
same products 7, 8 and 11 were obtained in similar yields
(6, 39 and 38%).
4.5.1. 6,7-Hydroxy-9-carbonitrile-15,16-epoxylabda-
13(16),14-dienol (4). Colourless oil; [a]1D9C37 (c 0.5,
CHCl3); IR nmax 3437, 2928, 2859, 2852, 2221, 1365, 1160,
1
1023, 871, 784 cmK1; H NMR (CDCl3, 400 MHz) d 1.03
(3H, m, H3-18 or H3-19); 1.25 (3H, m, H3-19 or H3-18);
1.26 (3H, m, H3-20); 1.27 (3H, m, H3-17); 1.28 (1H, m,
H-3a); 1.40 (1H, m, H-3b); 1.44 (1H, d, JZ1.6 Hz, H-5);
1.53 (1H, dd, JZ6.4, 2.7 Hz, H-11a); 1.55 (1H, m, H-2a);
1.60 (2H, m, H2-1), 1.66 (1H, m, H-2b); 1.96 (1H, ddd, JZ
14.4, 12.5, 6.9 Hz, H-11b); 2.11 (1H, m, H-8); 2.65 (2H, m,
H2-12); 3.53 (1H, dd, JZ10.9, 3.5 Hz, H-7); 4.28 (1H, dd,
JZ3.1, 1.7 Hz, H-6); 6.27 (1H, d, JZ1.8 Hz, H-14); 7.24
(1H, br s, H-16); 7.35 (1H, t, JZ1.5 Hz, H-15); 13C NMR
(CDCl3, 100 MHz) d 13.2 (q, C-17); 17.1 (q, C-20); 18.6 (t,
C-2); 24.5 (q, C-18 or C-19); 24.6 (t, C-12); 31.7 (t, C-11);
33.4 (q, C-19 or C-18); 34.4 (s, C-4); 37.6 (t, C-1); 38.0
(d, C-8); 41.9 (s, C-10); 43.0 (t, C-3); 51.2 (d, C-5); 54.1 (s,
C-9); 69.6 (d, C-6); 74.3 (d, C-7); 110.6 (d, C-14); 121.4 (s,
C-21); 124.0 (s, C-13); 138.7 (d, C-16); 143.0 (d, C-15);
HRFABMS m/z 345.2304 (calcd for C21H31NO3 [(MC
H)C], 345.2304).
4.3.1. 11,12-Dihydro-7-hydroxyhedychenone (11).
Yellow oily solid; [a]2D5C2 (c 0.89, CHCl3), lit.16C0.7;
IR nmax 3382 (br), 2930, 2863, 1692, 1615, 1615, 1471,
1385, 1026, 874, 774 cmK1 1H and 13C NMR data
;
presented in Table 1; EIMS m/z (rel. int.) 316 [MC] (6),
301 (100), 283 (43), 255 (17), 229 (12), 192 (17), 175 (12),
161 (26), 133 (14), 96 (11); HRFABMS m/z 317.2116 (calcd
for C20H29O3 [(MCH)C], 317.2117).
4.4. KCN mediated hydrolysis of 9 and 10
4.6. In planta test methods
A solution of a 5:2 mixture of 9 and 10 (152 mg, 0.4 mmol)
and KCN (70 mg, 1.08 mmol) in 95% EtOH (3 mL) was
refluxed (24 h). The ethanol was removed in vacuo, and the
white residue taken up in water (5 mL) and extracted with
EtOAc (3!5 mL). The organic fractions were combined,
dried (anhydrous MgSO4) and concentrated to give a pale
For evaluations in 1 day protectant tests, samples of the
compounds were dissolved in acetone at 2000 ppm, then
diluted in acetone to 500 and 125 ppm. Samples were then
brought to final concentrations of 200, 50 and 12.5 ppm by
addition of 9 volumes of milli-Q water containing 110 ppm
Triton X-100. Applications were made in 20 mL spray