Five phloroglucinol-monoterpene adducts from Eucalyptus grandis

Article abstract of DOI:10.1016/S0031-9422(98)00289-1

Five new euglobals possessing the phloroglucinol-monoterpene structure, euglobals G8-G12, together with a known euglobal-IIc were isolated from the hexane fraction of the methanol extract of the leaves of Eucalyptus grandis. Euglobal-G8 is an adduct of formyl-isovaleroyl-phtoroglucinol and γ- terpinene whereas -G9, -G10 and -G11 have the same phloroglucinol moiety fused with α-terpinene, while Euglobal-G12 has terpinolene fused with the same phloroglucinol moiety. The structures of these compounds were elucidated on the basis of spectral evidences. Biomimetic synthesis of euglobals suggests that these compounds are derived biogenetically by the Diels-Alder type cycloaddition of the corresponding terpenes with an ortho-quinone methide generated from grandinol.

Full text of DOI:10.1016/S0031-9422(98)00289-1

Phytochemistry Vol. 49, No. 6, pp. 1699±1704, 1998
# 1998 Elsevier Science Ltd. All rights reserved
Printed in Great Britain
0031-9422/98/$ - see front matter
PII: S0031-9422(98)00289-1
FIVE PHLOROGLUCINOL-MONOTERPENE ADDUCTS
FROM EUCALYPTUS GRANDIS
KAZUHIRO UMEHARA, INDER PAL SINGH, HIDEO ETOH,* MIDORI TAKASAKI and
TAKAO KONOSHIMA
Department of Applied Biological Chemistry, Shizuoka University, 836 Ohya, Shizuoka, 422-8529,
Japan; Kyoto Pharmaceutical University, Misasagi, Yamashina-ku, Kyoto, 607-8414, Japan
(Received 23 February 1998)
Key Word IndexÐEucalyptus grandis; Myrtaceae, euglobal-G8; euglobal-G9; euglobal-G10;
euglobal-G11; euglobal-G12; phloroglucinol-monoterpene adducts.
AbstractÐFive new euglobals possessing the phloroglucinol-monoterpene structure, euglobals G8±G12,
together with a known euglobal-IIc were isolated from the hexane fraction of the methanol extract of the
leaves of Eucalyptus grandis. Euglobal-G8 is an adduct of formyl-isovaleroyl-phloroglucinol and g-terpinene
whereas ±G9, ±G10 and ±G11 have the same phloroglucinol moiety fused with a-terpinene, while Euglo-
bal-G12 has terpinolene fused with the same phloroglucinol moiety. The structures of these compounds
were elucidated on the basis of spectral evidences. Biomimetic synthesis of euglobals suggests that these
compounds are derived biogenetically by the Diels±Alder type cycloaddition of the corresponding terpenes
with an ortho-quinone methide generated from grandinol. # 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION
RESULTS AND DISCUSSION
The hexane fraction of the methanol extract of
the air dried leaves of E. grandis was fractionated
as outlined in the Experimental section to give
euglobal-G8 (1), -G9 (2), -G10 (3), -G11 (4), -G12
(5) and -IIc (6).
We have reported elsewhere on the presence of
several bioactive phloroglucinol compounds from
the leaves of di€erent species of Eucalyptus [1±5].
These phloroglucinol compounds exhibit interesting
biological activities. We have recently isolated two
new euglobals, euglobal-G6 and -G7, from the
hexane fraction of the methanol extract of the
leaves of E. grandis [6]. Further investigation of the
hexane fraction has now resulted in the isolation of
®ve new euglobals, named euglobals G8±G12, and
a known euglobal-IIc [7]. Euglobals G1±G5, from
the leaves of E. grandis, have been reported as in-
hibitors of Epstein Barr Virus (EBV) activation [8].
In this paper, we report on the structure elucidation
of euglobals G8±G12, and biomimetic synthesis of
euglobal-G8, -G9, -G10 and -G12. These euglobals
were also tested for inhibitory activity against EBV
activation induced by 12-O-tetradecanoyl phorbol-
13-acetate (TPA).
The high-resolution mass spectrum of each of the
above compounds (1±5) established that they all
had the same molecular formula, C23H30O5. In
addition, the UV spectra were virtually super-
imposable on those of other euglobals [6].
The 1H NMR spectrum of euglobal-G8 (1) was
very similar to that of euglobal-G6 (7) [6]. It dif-
fered from euglobal-G6 in the position of attach-
ment of an isopropyl and a methyl group in the
monoterpene part as shown by the HMBC spec-
trum. The methyl protons of an isopropyl group
showed HMBC correlations with an oxy carbon (C-
1') while a singlet three proton signal (H-7') was
correlated with two sp2 carbons. These showed that
the isopropyl group was present at C-1' and another
methyl was attached to C-4'. Other HMBC corre-
lation con®rmed that the formyl group was located
at C-3 and the isovaleroyl group at C-5. All these
data con®rmed the structure as shown for euglobal-
G8 (Fig. 1.).
*Author to whom correspondence should be addressed.
Phone: 0081 54 238 4884; Fax: 0081 54 238 4884; E-
mail: acheto@agr.shizuoka.ac.jp.
1699

1700
K. UMEHARA et al.
Fig. 1. Structures of euglobals from E. grandis.
The structure of euglobal-G9 (2) was established valeroyl group was located at position 5. Other sig-
by using 2D NMR spectroscopy. The 13C NMR ni®cant HMBC and 1H±1H COSY correlations are
and DEPT spectra of 2 showed 23 carbons and 28 shown in Fig. 2. Strong throughspace interaction
1
hydrogens bound to carbon atoms. The H and 13C between Me-7' and H-1' con®rmed the cis stereo-
NMR spectra established that 2 contained a phloro- chemistry at these centres of euglobal-G9. The
glucinol moiety (dC 171.7, 168.1, 160.4, 103.7, 103.6 structure of euglobal-G9 was thus established as
and 100.3) containing one aldehyde group (dC shown in the Fig. 1.
192.0) and one isovaleroyl group [dC 206.3 (s), 52.7
Euglobal-G10 (3) had the same molecular for-
(t), 25.0 (d), 2 Â22.8 (q)]. The presence of a doublet mula and a similar UV spectrum as compound 2.
carbon (d 118.1) and a singlet carbon (d 148.5) in The 1H NMR spectrum of 2 also showed the pre-
the 13C NMR spectrum and a one proton singlet at sence of four doublet methyls and one singlet
d 5.43 suggested the presence of a trisubstituted methyl besides one ole®nic proton. The 13C NMR
double bond as in euglobal-G6 (7) and ±G7 (8). spectrum was similar to compound 2 with import-
The structure of monoterpene part and its linkage ant di€erences being observed only in the HMBC
1
to the phloroglucinol unit was elucidated by H±1H and di€erential NOE experiments. In the HMBC
COSY, HSQC and HMBC as shown in Fig. 2. An experiment, the phenolic proton at position 6 as
HMBC correlation from the oxymethine proton well as the formyl proton H-8 were correlated with
(H-1') to both the ole®nic carbons (C-2' and 3') C-5 and ±6. In the di€erential NOE experiment, the
suggested that the double bond was present at pos- formyl proton H-8 showed strong throughspace
ition 2', 3'. Similarly the methyl protons at 7' were interaction with both phenolic protons (4-OH and
correlated with two triplet carbons, C-7 and C-5', 6-OH). These data con®rmed that the formyl group
showing that the methyl was attached to carbon was linked to C-5 and the isovaleroyl group to C-3.
C-6'. HMBC correlations from H-7 to carbons at Interaction between Me-7' and H-1' indicated a cis
C-1, ±2, and ±6 and from phenolic proton at d stereochemistry at C-1' and ±6'. These data showed
15.42 (6-OH) to C-1, ±5, and ±6 and from formyl that 2 and 3 di€er from each other in the attach-
proton at d 10.05 to C-3 and ±4 suggested that the ment of the formyl and isovaleroyl groups on the
formyl group was located at position 3 and the iso- phloroglucinol ring (Fig. 1).

Five phloroglucinol-monoterpene adducts from Eucalyptus grandis
1701
Fig. 2. Structure elucidation of new euglobals G8±G12 (1-5).
The structure of euglobal-G11 (4) was similarly In order to rationalize the biogenesis of euglo-
established on the basis of its 2D NMR spectral bals, we attempted the synthesis of these com-
data. Compound 4 di€ers from 2 in the positions of pounds and directed our attention to the synthesis
attachment of the isopropyl and methyl groups in of grandinol. We synthesized grandinol by a route
the monoterpene moiety. Compound 4 has an iso- di€erent from that reported in literature [10].
propyl attached to C-6' and methyl attached to Reduction of 2,4,6-trihydroxy benzaldehyde with
C-3'.
sodium cyanoborohydride gave trihydroxy toluene.
The 1H NMR spectrum of euglobal-G12 (5) We selected sodium cyanoborohydride because
showed the presence of two doublet methyl signals this reaction proceeds under suciently mild
of an isovaleroyl group besides three other singlet conditions [11]. The isovaleroyl functionality was
methyl signals. Methyl protons H3-9' and ±10' were introduced via Friedel±Crafts acylation with iso-
correlated with C-8' and ±1' while methyl protons valeroyl chloride in the presence of AlCl3 as
H3-7' were correlated with C-3', ±4' and ±5'. catalyst [12]. Finally, the forymlation was achieved
Methylene protons H2-7 were correlated with C-1',
by using triethyl orthoformate in the presence of
±8', ±9', ±1, ±2 and ±6. These data and other AlCl3 [12]. Grandinol was thus synthesized in three
HMBC and 1H±1H COSY correlations con®rmed steps in 18% overall yield. All the products were
the structure of 5 as shown in Fig. 1. identi®ed by a comparison of their spectral data
Biogenetically 1±5 may be formed by Diels±Alder with those in literature [9, 10].
type cyclo-addition of corresponding monoterpene
The key step in the synthesis of euglobals was the
to an o-quinone methide derived from grandinol (9) Diels±Alder cycloaddition of the monoterpene with
(Fig. 3.) [9]. Euglobal-G8 (1) is assumed to be de- the o-quinone methide generated in situ by DDQ
rived by Diels±Alder cycloaddition of the s-quinone oxidation of grandinol [13]. Accordingly, grandinol
methide with g-terpinene, the double bond at pos- was reacted with a-terpinene in the presence of
ition 4 and 5 being involved in the cycloaddition DDQ and nitromethane to give euglobal-G9 (2),
reaction. Euglobals G9±G11 (2±4) are derived from -G10 (3) in 9.3 and 5.9% yield, respectively. Both
a-terpinene, -G9 (2) and -G10 (3) with the partici- these synthetic euglobals were identi®ed by a com-
pation of the 1,2 double bond and -G11 (4) with parison of their spectral data with those of natural
the participation of the 3,4 double bond. Euglobal- products. Similarly reaction with g-terpinene gave
G12 (5) is derived by the cycloaddition of the o-qui- euglobal-G8 (1), -G6 (7) and -G7 (8) while reaction
none methide with terpinolene.
with terpinolene gave euglobal-G12 (5). All these

1702
K. UMEHARA et al.
Fig. 3. Proposed biogenetic pathways for euglobals G8±G12.
products were identi®ed by comparison of their (9:1) was subjected to HPLC and successive recycle
HPLC retention times with those of natural pro- HPLC on ODS (MeOH±AcOH±H2O, 100:5:3) to
ducts.
give compounds 1 (36 mg), 2 (40 mg), 3 (20 mg), 4
The synthesis of 1±3 and 5 by Diels±Alder type (10 mg), 5 (6 mg) and 6 (25 mg) [7] in 0.0036,
cycloaddition indicates that euglobals are derived 0.0040, 0.0020, 0.0010, 0.0006 and 0.0025% yield,
biogenetically by reactions similar to these synthetic respectively.
routes.
Euglobal-G8 (1)
Compounds 1±3 and 5 were tested for inhibition
of Epstein Barr Virus early antigen activation
induced by TPA. Compounds 1, 2 and 5 showed
around 100% inhibition at 1000 mol ratio/TPA
while maintaining 70% viability of the Raji cells.
This activity was comparable to the activity of
euglobal-G1, ±G2 and ±G4. Compound 3 showed
about 90% inhibition at the same concentration.
Oil, [a]D 08 (CHCl3 c 0.1). HREI-MS m/z
386.2093 [M]+ ( 0.1 mmu for C23H30O5)]; UV
lmax. (hexane) nm (log E): 275 (3.98) and 341 (2.94);
IR nmax. (CHCl3) cm 1: 1626, 1427, 1292 and 1184;
1H NMR (CDCl3, 500 MHz) d ppm: 15.35 (1H, s,
6-OH), 14.43 (1H, s, 4-OH), 10.02 (1H, s, H-8),
5.24 (1H, d, J = 1.5 Hz, H-3'), 2.97 (2H, d,
J = 6.7 Hz, H-10), 2.62 (1H, dd, J = 16.6 and
5.7 Hz, H-7), 2.38 (1H, dd, J = 16.5 and 5.2 Hz, H-
7), 2.32 (1H, m, H-6'), 2.27 (2H, m, H-2'), 2.26 (1H,
m, H-11), 2.15 (1H, septet, J = 6.7 Hz, H-8'), 2.06
(1H, m, H-5'), 1.87 (1H, dd, J = 17.4 and 8.5 Hz,
H-5'), 1.65 (3H, brs, H-7'), 1.00 (3H, d, J = 7.0 Hz,
H-10'), 0.98 (6H, d, J = 7.0 Hz, H-12 and 13), 0.96
(3H, d, J = 6.7 Hz, H-9'); 13C NMR (CDCl3,
125 MHz): Table 1.
EXPERIMENTAL
General
Mps uncorr.; NMR: 500 MHz (1H) and 125 MHz
(13C) in CDCl3 with TMS as int. standard; TLC:
Merck HPTLC Fertigplatten RP-18 WF254s and
Merck DC Fertigplatten kieselgel 60F254, the chro-
matograms being visualized under UV light 254 nm
or by spraying with 50% EtOH/H2SO4; UV: hex-
ane; IR: CHCl3.
Euglobal-G9 (2)
Oil, [a]D 08 (CHCl3 c 0.1). HREI-MS m/z
386.2114 [M]+ (+2.0 mmu for C23H30O5)]; UV
Plant material
l
max. (hexane) nm (log E): 275 (4.39) and 341 (3.35);
Eucalyptus grandis was grown at the research IR nmax. (CHCl3) cm 1: 1626, 1427, 1290 and 1169;
farm of Shizuoka University.
1H NMR (CDCl3, 500 MHz) d ppm: 15.42 (1H, s,
6-OH), 14.48 (1H, s, 4-OH), 10.05, (1H, s, H-8),
5.43 (1H, s, H-2'), 4.47 (1H, s, H-1'), 2.97 (2H, d,
Isolation of euglobals
The MeOH extract of the air-dried leaves of E. J = 6.7 Hz, H-10), 2.44 (1H, d, J = 16.5 Hz, H-7),
grandis (1 kg) was successively extracted with hex- 2.26 (1H, m, H-11), 2.20 (1H, d, J = 15.6 Hz, H-7),
ane and CH2Cl2. The hexane fr was separated into 2.20 (1H, m, H-4'), 2.19 (1H, m, H-8'), 2.08 (1H, m,
di€erent frs by chromatography on silica gel (hex- H-4'), 1.76 and 1.54 (1H each, m, H-5'), 1.04 (3H, s,
ane±EtOAc). The fr eluted with hexane±EtOAc H-7'), 1.01 (6H, d, J = 6.7 Hz, H-9' and 10'), 0.98

Five phloroglucinol-monoterpene adducts from Eucalyptus grandis
Table 1. 13C NMR spectral data of euglobals G8±G12 (1±5)
1703
C
1
2
3
4
5
1
2
3
4
5
6
7
100.4 s
161.2 s
104.2 s
168.3 s
103.6 s
171.7 s
21.1 t
100.3 s
160.4 s
103.7 s
168.1 s
103.6 s
171.7 s
25.7 t
99.4 s
100.8 s
160.8 s
103.7 s
168.0 s
103.7 s
171.8 s
20.6 t
100.0 s
162.1 s
104.1 s
170.3 s
104.7 s
167.2 s
31.0 t
161.8 s
103.8 s
169.9 s
104.6 s
167.4 s
26.9 t
8
9
191.8 d
206.4 s
52.7 t
25.1 d
22.8 q
22.8 q
82.4 s
192.0 d
206.3 s
52.7 t
25.0 d
22.8 q
22.8 q
80.1 d
118.1 d
148.5 s
23.2 t
31.3 t
28.8 s
25.4 q
34.5 d
21.3 q
21.3 q
192.4 d
206.1 s
53.1 t
25.7 d
22.8 q
22.8 q
79.9 d
117.2 d
149.3 s
23.3 t
191.9 d
206.4 s
52.7 t
25.1 d
22.8 q
22.8 q
76.8 d
120.7 d
139.7 s
27.3 t
24.2 t
33.6 s
22.9 q
29.6 d
16.9 q
16.7 q
192.5 d
206.0 s
52.3 t
24.4 d
22.7 q
22.5 q
83.5 s
27.2 t
10
11
12
13
1'
2'
3'
4'
5'
6'
7'
8'
9'
10'
28.5 t
116.9 d
132.1 s
33.7 t
29.1 d
23.1 q
30.9 d
16.1 q
17.0 q
118.2 d
133.3 s
30.5 t
30.1 t
28.2 s
24.7 q
24.6 d
21.3 q
21.2 q
25.5 t
23.2 q
32.6 s
25.0 q
23.2 q
Spectra recorded in CDCl3
Multiplicity assigned by the DEPT experiment; s = C, d = CH, t = CH2, q = CH3.
(6H, d, J = 6.7 Hz, H-12 and 13); 13C NMR J = 7.0 Hz, H-10'); 13C NMR (CDCl3, 125 MHz):
(CDCl3, 125 MHz): Table 1.
Table 1.
Euglobal-G12 (5)
Euglobal-G10 (3)
Oil, [a]D 08 (CHCl3 c 0.1). HREI-MS m/z
Oil, [a]D 08 (CHCl3 c 0.1). HREI-MS m/z
386.2086 [M]+ ( 0.8 mmu for C23H30O5)]; UV
l
386.2090 [M]+ ( 0.4 mmu for C23H30O5)]; UV
l
max. (hexane) nm (log E): 273 (4.93) and 342 (4.08);
max. (hexane) nm (log E): 273 (4.23) and 344 (3.34);
IR nmax. (CHCl3) cm 1: 1612, 1415, 1309 and 1120;
1H NMR (CDCl3, 500 MHz) d ppm: 15.58 (1H, s,
4-OH), 13.19 (1H, s, 6-OH), 10.20 (1H, s, H-8),
5.40 (1H, s, H-3'), 2.99 (1H, dd, J = 16.8 and
6.1 Hz, H-10), 2.64 (1H, dd, J = 17.1 and 7.3 Hz,
H-10), 2.47 and 2.39 (1H each, d, J = 17.1 Hz, H-
7), 2.43 and 2.25 (1H, m, H-5'), 2.21 (1H, m, H-11),
1.94 and 1.72 (1H each, m, H-6'), 1.94 (2H, m, H-
2'), 1.71 (3H, s, H-7'), 1.09 (3H, s, H-9'), 1.00 (3H,
s, H-10'), 0.93 (3H, d, J = 7.0 Hz, H-12), 0.92 (3H,
d, J = 7.0 Hz, H-13); 13C NMR (CDCl3,
125 MHz): Table 1.
IR nmax. (CHCl3) cm 1: 1612, 1427, 1315 and 1190;
1H NMR (CDCl3, 500 MHz) d ppm: 15.38 (1H, s,
4-OH), 13.21 (1H, s, 6-OH), 10.18 (1H, s, H-8),
5.52 (1H, s, H-2'), 4.46 (1H, s, H-1'), 2.88 (2H, d,
J = 6.7 Hz, H-10), 2.50 (1H, d, J = 16.2 Hz, H-7),
2.25 (1H, d, J = 16.5Hz, H-7), 2.25 (1H, m, H-8'),
2.19 (1H, m, H-11), 2.12 (2H, m, H-4'), 1.72 and
1.48 (1H each, m, H-5'), 1.04 (3H, s, H-7'), 1.03
(6H, d, J = 7.6 Hz, H-9' and 10'), 0.98 (3H, d,
J = 6.7 Hz, H-12), 0.97 (3H, d, J = 6.7 Hz, H-13);
13C NMR (CDCl3, 125 MHz): Table 1.
Euglobal-G11 (4)
Synthesis of trihydroxy toluene
Oil, [a]D 08 (CHCl3 c 0.1). HREI-MS m/z To a soln of 2,4,6-trihydroxy benzaldehyde
386.2084 [M]+ ( 1.0 mmu for C23H30O5)]; UV (308 mg, 2 mmol) in THF (10 ml) was added methyl
lmax. (hexane) nm (log E): 275 (4.49) and 341 (3.46); orange (0.1 mg, dissolved in H2O) and sodium cya-
IR nmax. (CHCl3) cm 1: 1626, 1436, 1290 and 1176; noborohydride (380 mg, 6 mmol). The soln was stir-
1H NMR (CDCl3, 500 MHz) d ppm: 15.41 (1H, s, red for 16 hr keeping the pH at 4.0 (monitored by
6-OH), 14.44 (1H, s, 4-OH), 10.03 (1H, s, H-8), red colour of indicator) by adding 1N\HCl [11].
5.46 (1H, d, J = 1.8 Hz, H-2'), 4.70 (1H, s, H-1'), The reaction mixture was extracted three times with
2.97 (2H, d, J = 7.3 Hz, H-10), 2.45 (1H, d, EtOAc, dried over anhydrous Na2SO4 and evapor-
J = 16.8 Hz, H-7), 2.27 (1H, d, J = 16.5 Hz, H-7), ated. The crude product was puri®ed by silica gel
2.25 (1H, m, H-11), 2.07 (1H, m, H-4'), 1.82 (1H, CC (CHCl3±EtOAc, 2:1) to give 2,4,6-trihydroxyto-
m, H-8'), 1.70 (3H, s, H-7'), 1.56 (2H, m, H-5'), 0.99 luene (120 mg, yield 42%). Mp 210±2118. UV lmax
1
(3H, d, J = 6.7 Hz, H-12), 0.98 (3H, d, J = 6.7 Hz, (MeOH) nm (log E): 206 (4.56); IR nmax (nujol) cm
:
H-13), 0.95 (3H, d, J = 7.0 Hz, H-9'), 0.87 (3H, d, 3400, and 1620; 1H NMR (CD3OD, 500 MHz) d:

1704
K. UMEHARA et al.
5.86 (2H, s), 1.99 (3H, s); 13C NMR (CD3OD, min, detection: 274 nm, solvent: MeOH±AcOH±
125 MHz) d: 157.7 (s), 156.7 (s), 103.6 (s), 95.4 (d), H2O, 100:3:5) to yield euglobal-G12 (5, tR
and 8.0 (q).
43.0 min), identi®ed by comparison of its HPLC tR
with that of an authentic sample.
Synthesis of 3-isovaleroyl-2,4,6-trihydroxytoluene
Biological evaluation
Trihydroxytoluene was reacted with isovaleryl
chloride according to the method described in the
literature [12] and the product was identi®ed by by using the same method as previously
The inhibition of EBV-EA activation was assayed
comparison with the data in literature [9, 10].
described [8].
Synthesis of grandinol (9)
AcknowledgementsÐThe authors thank Drs. H.
Tokuda and H. Nishino of Kyoto Prefectural
University of Medicine for biological evaluation of
the compounds.
The formyl group was introduced by reaction
with triethylorthoformate according to the estab-
lished method [12]. Grandinol was identi®ed by a
comparison of its spectral data with those in
literature [9, 10].
Diels±Alder reaction of 9 and a-terpinene
REFERENCES
To a soln of grandinol (9, 30 mg) in nitromethane
(5 ml) was added DDQ (27 mg). The soln was
warmed to 608 and then a soln of a-terpinene
(49 mg) in nitromethane (5 ml) added dropwise. The
reaction mixture was re¯uxed for 30 min. The sol-
vent was evaporated and the crude product was
subjected to HPLC on ODS (column: YMC, D-
ODS-5 S-5 120A ODS, ¯ow rate: 10 ml/min, detec-
tion: 274 nm, solvent: MeOH±AcOH±H2O, 100:3:5)
to yield 2 (4.3 mg, tR 39.8 min) and 3 (2.7 mg, tR
31.8 min) identi®ed by a comparison of their spec-
tral data with those of natural products.
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Haruna, M. and Ito, K., Journal of Natural
Products, 1991, 54, 1082.
8. Takasaki, M., Konoshima, T., Kozuka, M. and
Tokuda, H., Biological Pharmaceutical Bulletin,
1995, 18, 435.
9. Crow, W. D., Osawa, T., Paton, D. M. and
Willing, R. R., Tetrahedron Letters, 1977, 1073.
10. Yuste, F., Sanchez-Obregon, R. and Walls, F.,
Synthesis of grandinol. Tetrahedron letters,
1978, 4869.
Diels±Alder reaction of 9 and g-terpinene
To a soln of grandinol (9, 3 mg) in nitromethane
(3 ml) was added DDQ (2.7 mg). The soln was
warmed to 608 and then a soln of g-terpinene
(4.9 mg) in nitromethane (2 ml) added dropwise.
The reaction mixture was re¯uxed for 30 min. The
solvent was evaporated and the crude product was
subjected to analytical HPLC on ODS (column:
YMC, D-ODS-5 S-5 120A ODS, ¯ow rate: 10 ml/
min, detection: 274 nm, solvent: MeOH±AcOH±
H2O, 100:3:5) and the products, euglobal-G6 (7, tR
66.9 min), -G7 (8, tR 44.5 min) and -G8 (1, tR
68.8 min) were identi®ed by a comparison of their
HPLC tR values with those of authentic samples.
Diels±Alder reaction of 9 and terpinolene
To a soln of grandinol (9, 3 mg) in nitromethane 11. Elliger, C. A., Synthetic Communications., 1985,
(3 ml) was added DDQ (2.7 mg). The soln was 15, 1315.
warmed to 608 and then a soln of terpinolene 12. Chiba, K., Arakawa, T. and Tada, M.,
(4.9 mg) in nitromethane (2 ml) added dropwise. Chemical Communications, 1996, 1763.
The reaction mixture was re¯uxed for 30 min. The 13. Bolte, M. L., Crow, W. D., Takahashi, N.,
solvent was evaporated and the crude product was
subjected to analytical HPLC on ODS (column:
YMC, D-ODS-5 S-5 120A ODS, ¯ow rate: 10 ml/
Sakurai, A., Uji-ie, M. and Yoshida, S.,
Aricultural and Biological Chemistry, 1985, 49,
761.