Facile zeolite induced Fischer-indole synthesis: A new approach to bioactive natural product rutaecarpine

Article abstract of DOI:10.1016/j.tet.2004.02.037

Starting from glutaric anhydride (5) we have demonstrated an elegant six-step practical synthesis of bioactive natural product rutaecarpine (1a) via o-amidoglutaranilic acid formation, esterification, chemoselective ester reduction, intramolecular dehydrative cyclizations, hydrazone formation and zeolite induced Fischer-indole synthesis with 53% overall yield. The conditions employed in the present synthesis are mild, efficient and general.

Full text of DOI:10.1016/j.tet.2004.02.037

Tetrahedron 60 (2004) 3417–3420
Facile zeolite induced Fischer-indole synthesis: a new approach
to bioactive natural product rutaecarpineq
*
Santosh B. Mhaske and Narshinha P. Argade
Division of Organic Chemistry (Synthesis), National Chemical Laboratory, Pashan, Pune 411 008, India
Received 11 December 2003; revised 28 January 2004; accepted 19 February 2004
Dedicated to Dr. B. G. Hazra, OCS, NCL, Pune
Abstract—Starting from glutaric anhydride (5) we have demonstrated an elegant six-step practical synthesis of bioactive natural product
rutaecarpine (1a) via o-amidoglutaranilic acid formation, esterification, chemoselective ester reduction, intramolecular dehydrative
cyclizations, hydrazone formation and zeolite induced Fischer-indole synthesis with 53% overall yield. The conditions employed in the
present synthesis are mild, efficient and general.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
on the synthesis of bioactive natural products using cyclic
anhydrides as a potential precursors,15 we became interested
in total synthesis of rutaecarpine (1a). We felt that it would
be possible to design the five carbon six-membered ring C
Large numbers of quinazolinone alkaloids have been
isolated from a number of plants, animals and microorgan-
isms and synthesized in view of their well established
pharmacological activities.1 Development of new, elegant
synthetic routes to these bioactive quinazolinone alkaloids
and their precursors is a challenging task of current interest.2
The dried fruits of Evodia rutaecarpa have been used in
traditional Chinese medicine under the name Wu-Chu-ru3
and Shih-Hu4 as a remedy for headache, dysentery, cholera,
worm infections and postpartum.5 The drug extract contains
quinazolinocarboline alkaloids rutaecarpine (1a) and evo-
diamine (3b).6 Recently, callus tissue cultured from the
stem of Phellodendron amurense has been shown to
produce 1a, along with a variety of other alkaloids7
(Fig. 1). In recent literature, 1a and its derivatives have
been reported to possess strong analgesic,8 antiemetic,8
astringent,8 antihypertensive,8 uterotonic,9 TCDD-recep-
tor,10 atinociceptive,11 anti-inflammatory11 and cycloxy-
genase (COX-2) inhibitory8 activities. The rutaecarpine
(1a) was also found to suppress platelet plug formation
in mesenteric venules and increase intracellular Ca2þ in
endothelial cells.12 The first total synthesis of this important
bioactive natural product 1a was reported13 by Robinson
et al. in 1927 and since then several routes to 1a and its
derivatives have been developed.14 In our on-going studies
q NCL Communication No. 6656.
Keywords: Glutaric anhydride; Mackinazolinone; Zeolite; Fischer indole
synthesis; Rutaecarpine.
*
Corresponding author. Tel./fax: þ91-20-25893153;
e-mail address: argade@dalton.ncl.res.in
Figure 1. Naturally occurring bioactive rutaecarpines and analogs.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.02.037

3418
S. B. Mhaske, N. P. Argade / Tetrahedron 60 (2004) 3417–3420
Scheme 1. Reagents, conditions and yields: (i) C6H6, 1,4-dioxane (2:1), room temperature, 2 h (98%); (ii) MeOH, H2SO4 (cat.), room temperature, 8 h (96%);
(iii) NaBH4, THF, reflux, 3 h, aqueous workup (86%); (iv) NaH, p-TsCl, THF, room temperature, 30 min (81%); (v) aniline, 30% HCl, NaNO2, AcOH, 25 to
5 8C, 8 h (98%); (vi) zeolite (H-Mordenite), AcOH, reflux, 5 h (82%).
in 1a from glutaric anhydride (5) and we herein report a
facile six-step synthesis of 1a (Scheme 1).
3. Conclusion
In summary, starting from glutaric anhydride, we have
demonstrated an elegant six-step total synthesis of bioactive
natural product rutaecarpine with 53% overall yield via
zeolite induced Fischer-indole synthesis. The present zeolite
induced Fischer-indole synthesis conditions are mild and
efficient compared to earlier known conditions and will be
useful to design several naturally occurring indole skele-
tons. The present practical approach to quinazolinone
alkaloid 1a is efficient, general, noteworthy and can be
used to design libraries of rutaecarpine analogs and
derivatives.
2. Results and discussion
The reaction of anthranilamide (4) with glutaric anhydride
(5) in benzene/1,4-dioxane (2:1) at room temperature
furnished the corresponding o-amidoglutaranilic acid (6)
in quantitative yield. The glutaranilic acid 6, on treatment
with methanol and catalytic amount of sulfuric acid at room
temperature, gave the corresponding methyl ester 8 in 96%
yield. We feel that the present esterification at room
temperature is plausibly taking place via the corresponding
isoimide 7. The ester 8 underwent smooth chemoselective
sodium borohydride reduction to yield intermediate alcohol
9 which, during the aqueous work-up, underwent an in situ
NaOH-catalyzed dehydrative ring closure to yield quinazo-
linone 10 in 86% yield. The quinazolinone 10, on treatment
with p-TsCl and sodium hydride in THF at room
temperature, underwent a facile intramolecular dehydrative
cyclization and furnished the bioactive natural product
mackinazolinone (11) [From Mackinalaya species]16 in
81% yield. The analytical and spectral data obtained for 11
was in complete agreement with reported data.16 Although
several routes to 11 are known,13,14,16 this is the first
approach starting from glutaric anhydride and has several
advantages. The mackinazolinone, on reaction with in situ
generated diazonium salt of aniline at 25 to 5 8C, gave the
corresponding hydrazone 12 in 98% yield.14i,j The hydra-
zone 12 on zeolite (H-Mordenite) induced Fischer-indole
synthesis17 in refluxing glacial acetic acid yielded the
bioactive natural product rutaecarpine (1a) in 82% yield.
The analytical and spectral data obtained for 1a was in
complete agreement with reported data.14f,m The overall
yield of 1a in six-steps was 53%. The rutaecarpine (1a) on
DDQ-oxidation is known to give dehydrorutaecarpine (1b)
in 77% yield.14f
4. Experimental
4.1. General
Melting points are uncorrected. Column chromatographic
separations were carried out on ACME silica gel (60–120
mesh). Anthranilamide, glutaric anhydride, sodium boro-
hydride, sodium hydride, p-toluenesulfonyl chloride and
aniline were obtained from Aldrich Chemical Co. Zeolite
H-Mordenite was obtained from PQ Zeolites (Netherlands)
and was heated at 500 8C for 6 h before using.
4.1.1. o-Amidoglutaranilic acid (6). To a solution of
glutaric anhydride (5, 2.28 g, 20 mmol) in benzene (50 mL)
was added a solution of anthranilamide (4, 2.72 g, 20 mmol)
in 1,4-dioxane (25 mL), in a dropwise fashion with constant
stirring at room temperature. Reaction mixture was further
stirred for 2 h and the formed precipitate was filtered in
vacuo and washed with benzene (2£25 mL). The obtained
compound 6 was used for the next step without any
further purification. Analytically pure 6 was obtained by
recrystallization from ethyl acetate.

S. B. Mhaske, N. P. Argade / Tetrahedron 60 (2004) 3417–3420
3419
Compound 6. 4.90 g (98% yield); crystalline solid; mp 131–
133 8C (ethyl acetate); 1H NMR (CD3OD, 300 MHz) d 2.01
(quintet, J¼9 Hz, 2H), 2.42 (t, J¼9 Hz, 2H), 2.49 (t,
J¼9 Hz, 2H), 7.16 (t, J¼9 Hz, 1H), 7.50 (t, J¼9 Hz, 1H),
7.75 (d, J¼9 Hz, 1H), 8.41 (d, J¼9 Hz, 1H); 13C NMR
(CD3OD, 75 MHz) d 21.9, 34.1, 37.9, 122.2, 122.6, 124.4,
129.4, 133.4, 140.2, 173.5, 173.6, 176.7; IR (Nujol) nmax
25.3 mmol) in THF (10 mL) was added a solution of alcohol
10 (2.5 g, 11.5 mmol) in THF (20 mL). To the above
reaction mixture, a solution of p-toluenesulfonyl chloride
(2.63 g, 14 mmol) in THF (10 mL) was added in a dropwise
fashion over a period of 15 min and the reaction mixture
was further stirred at room temperature for 30 min. Reaction
was quenched with water (10 mL), concentrated in vacuo
and extracted with ethyl acetate (100 mL). The organic
layer was washed with aqueous sodium bicarbonate
solution, water and brine. The organic layer was dried
over Na2SO4 concentrated and dried in vacuo. The crude
product was purified by silica gel column chromatography
using a mixture of ethyl acetate and petroleum ether (1:1) to
furnish 11.
3449, 3317, 3260, 2700–2500, 1688, 1680, 1634 cm21
.
Anal. Calcd for C12H14N2O4: C, 57.59; H, 5.64; N, 11.19.
Found: C, 57.72; H, 5.81; N, 11.03.
4.1.2. Methyl o-amidoglutaranilate (8). To a solution of
acid 6 (4.50 g, 18 mmol) in methanol (50 mL) was added
two drops of H2SO4 and the reaction mixture was stirred
at room temperature for 8 h. The reaction mixture was
concentrated in vacuo. The residue was dissolved in ethyl
acetate and washed with aqueous sodium bicarbonate
solution, water, brine and the organic layer was dried over
Na2SO4. The organic layer was concentrated in vacuo to
obtain ester 8. The obtained ester 8 was used for the next
step without any further purification. Analytically pure 8
was obtained by recrystallization from benzene.
Compound 11. 1.86 g (81% yield); crystalline solid; mp 99–
101 8C (hexane) (lit.16 mp 98.5–99.5 8C); 1H NMR (CDCl3,
500 MHz) d 1.96 (quintet, J¼10 Hz, 2H), 2.02 (quintet, J¼
10 Hz, 2H), 3.00 (t, J¼10 Hz, 2H), 4.08 (t, J¼10 Hz, 2H),
7.42 (t, J¼10 Hz, 1H), 7.60 (d, J¼10 Hz, 1H), 7.71 (t, J¼
10 Hz, 1H), 8.26 (d, J¼10 Hz, 1H); 13C NMR (CDCl3,
125 MHz) d 19.2, 22.0, 31.7, 42.2, 120.3, 125.9, 126.2,
126.5, 134.0, 147.2, 154.8, 162.0; IR (Nujol) nmax 1657,
1612, 1587, 1566, 1462 cm21. Anal. Calcd for C12H12N2O:
C, 71.98; H, 6.04; N, 13.99. Found: C, 72.08; H, 6.19; N,
14.12.
Compound 8. 4.56 g (96% yield); crystalline solid; mp 98–
100 8C (C6H6); 1H NMR (CDCl3, 500 MHz) d 2.06 (quintet,
J¼10 Hz, 2H), 2.43 (t, J¼10 Hz, 2H), 2.47 (t, J¼10 Hz,
2H), 3.68 (s, 3H), 6.15 (bs, 1H), 6.48 (bs, 1H), 7.06 (t,
J¼10 Hz, 1H), 7.48 (t, J¼10 Hz, 1H), 7.55 (d, J¼10 Hz,
1H), 8.61 (d, J¼10 Hz, 1H), 11.24 (s, 1H); 13C NMR
(CDCl3, 125 MHz) d 20.5, 33.0, 37.1, 51.5, 118.7, 121.3,
122.5, 127.4, 133.0, 139.9, 171.0, 171.6, 173.5; IR (Nujol)
4.1.5. 6-Phenylhydrazono-6,7,8,9-tetrahydro-11H-pyrido-
[2,1-b]quinazolin-11-one (12). Phenyldiazonium chloride
was prepared from aniline (512 mg, 5.5 mmol) in 20%
hydrochloric acid (5 mL) at 0 8C using a solution of sodium
nitrite (380 mg, 5.5 mmol) in water (5 mL). The reaction
mixture was diluted with acetic acid (5 mL) and then was
adjusted to pH 4 using sodium acetate. To this solution of
phenyldiazonium chloride was added dropwise a solution of
the quinazolinone 11 (1.00 g, 5.0 mmol) in 50% acetic acid
(10 mL) at 0 8C over a period of 15 min. The reaction
mixture was further stirred at 0 8C for 3 h and then allowed
to stand overnight in a refrigerator. The precipitated
crystalline compound was filtered off, washed with water,
dried in vacuo to obtain pure 12.
n
max 3337, 3273, 3179, 1740, 1680, 1678, 1616 cm21. Anal.
Calcd for C13H16N2O4: C, 59.08; H, 6.10; N, 10.60. Found:
C, 58.97; H, 6.18; N, 10.69.
4.1.3. 2-(4-Hydroxybutyl)quinazolin-4(1H)-one (10). To
a solution of ester 8 (4.00 g, 15 mmol) in THF (50 mL) was
added NaBH4 (2.88 g, 76 mmol) and the reaction mixture
was refluxed for 3 h under an argon atmosphere. The
reaction mixture was allowed to cool to room temperature
and slowly quenched with water (50 mL). The reaction
mixture was further stirred for 1 h at room temperature and
then acidified with acetic acid. The reaction mixture was
then concentrated and dried in vacuo. The residue was
stirred with THF (100 mL) for 1 h and the organic layer
was filtered through celitew, dried over Na2SO4 and
concentrated in vacuo. The obtained crude product was
purified by silica gel column chromatography using a
mixture of ethyl acetate and methanol (99:1) to furnish 10.
Compound 12. 1.50 g (98% yield); yellow crystalline solid;
1
mp 184–186 (PrOH) (lit.14j mp 182–184 8C); H NMR
(CDCl3, 500 MHz) d 2.06 (quintet, J¼10 Hz, 2H), 2.79 (t,
J¼10 Hz, 2H), 4.02 (t, J¼5 Hz, 2H), 6.89 (t, J¼10 Hz, 1H),
7.20 (d, J¼10 Hz, 2H), 7.25 (t, J¼10 Hz, 2H), 7.39 (t, J¼
10 Hz, 1H), 7.57 (d, J¼10 Hz, 1H), 7.68 (t, J¼10 Hz, 1H),
8.20 (d, J¼10 Hz, 1H), 14.56 (s, 1H); 13C NMR (CDCl3,
125 MHz) d 21.3, 31.0, 43.0, 113.5, 120.2, 121.6, 124.0,
126.3, 126.6, 126.9, 129.2, 134.1, 143.7, 145.5, 147.3,
161.3; IR (CHCl3) nmax 3018, 1670, 1607 cm21. Anal.
Calcd for C18H16N4O: C, 71.03; H, 5.30; N, 18.41. Found:
C, 70.89; H, 5.41; N, 18.66.
Compound 10. 2.84 g (86% yield); crystalline solid; mp
175–177 8C (ethyl acetate); 1H NMR (CD3OD, 500 MHz) d
1.66 (quintet, J¼10 Hz, 2H), 1.90 (quintet, J¼10 Hz, 2H),
2.73 (t, J¼ 10 Hz, 2H), 3.63 (t, J¼10 Hz, 2H), 7.50 (t,
J¼10 Hz, 1H), 7.65 (d, J¼10 Hz, 1H), 7.80 (t, J¼10 Hz,
1H), 8.19 (d, J¼10 Hz, 1H); 13C NMR (CD3OD, 125 MHz)
d 25.3, 33.0, 35.9, 62.4, 121.9, 127.2, 127.3, 127.6, 135.9,
150.1, 159.6, 164.5; IR (Nujol) nmax 3398, 3173, 1686,
1614, 1468 cm21. Anal. Calcd for C12H14N2O2: C, 66.04;
H, 6.47; N, 12.83. Found: C, 66.11; H, 6.54; N, 12.98.
4.1.6. 8,13-Dihydroindolo[20,30:3,4]pyrido[2,1-b]quina-
zolin-5(7H)-one (rutaecarpine, 1a). To a solution of
hydrazone 12 (500 mg, 1.65 mmol) in freshly distilled
glacial acetic acid (10 mL) was added zeolite H-Mordenite
(2 g) and the stirred reaction mixture was refluxed for 5 h
under argon atmosphere. Acetic acid was distilled off in
vacuo and the residue was dried to the pump and then stirred
with THF (50 mL) for 1 h. The above reaction mixture was
4.1.4. 6,7,8,9-Tetrahydropyrido[2,1-b]quinazolin-11-one
(mackinazolinone, 11). To a stirred slurry of NaH (607 mg,

3420
S. B. Mhaske, N. P. Argade / Tetrahedron 60 (2004) 3417–3420
8. (a) Hibino, S.; Choshi, T. Nat. Prod. Rep. 2001, 18, 66.
(b) Tang, W.; Eisenbrand, G. E. Chinese drugs of plant origin.
Springer: Berlin, 1992; p 508.
filtered and dried over Na2SO4. The organic layer was
concentrated in vacuo and the obtained crude product was
purified by silica gel column chromatography using a
mixture of ethyl acetate and methanol (98:2) to furnish 1a.
9. King, C. L.; Kong, Y. C.; Wong, N. S.; Yeung, H. W.; Fong,
H. H. S.; Sankawa, U. J. Nat. Prod. 1980, 43, 577.
Compound 1a. 387 mg (82% yield); crystalline solid; mp
1
10. (a) Gillner, M.; Bergman, J.; Cambillau, C.; Gustafssoon, J. A.
Carcinogenesis 1989, 10, 651. (b) Rannug, U.; Sjogren, M.;
Rannug, A.; Gillner, M.; Toftgard, R.; Gustafssoon, J. A.;
Rosenkranz, H.; Klopman, G. Carcinogenesis 1991, 12, 2007.
11. Matsuda, H.; Yoshikawa, M.; Ko, S.; Iinuma, M.; Kubo, M.
Nat. Med. 1998, 52, 203.
257–259 8C (ethyl acetate) (lit.14j mp 258 8C); H NMR
(CDCl3, 500 MHz) d 3.15 (t, J¼10 Hz, 2H), 4.51 (t, J¼
10 Hz, 2H), 7.09 (t, J¼10 Hz, 1H), 7.17–7.28 (m, 2H), 7.34
(t, J¼10 Hz, 1H), 7.52–7.64 (m, 3H), 8.25 (d, J¼10 Hz,
1H), 9.62 (bs, 1H); 13C NMR (CDCl3, 125 MHz) d 19.7,
41.2, 112.1, 118.5, 120.1, 120.6, 121.2, 125.6 (2-carbons),
126.2, 126.5, 127.1, 127.3, 134.3, 138.4, 145.1, 147.4,
161.5; IR (CHCl3) nmax 3416, 1670, 1651, 1630,
1599 cm21. Anal. Calcd for C18H13N3O: C, 75.25; H,
4.56; N, 14.63. Found: C, 75.31; H, 4.67; N, 14.72.
12. (a) Wu, S. N.; Lo, Y. K.; Chen, H.; Li, H. F.; Chiang, H. T.
Neuropharmacology 2001, 41, 834. (b) Sheu, J. R.; Hung,
W. C.; Wu, C. H.; Lee, Y. M.; Yen, M. H. Br. J. Haematol.
2000, 110, 110. (c) Wang, G. J.; Shan, J.; Pang, P. K. T.; Yang,
M. C. M.; Chou, C. J.; Chen, C. F. J. Pharmacol. Exp. Therap.
1996, 270, 1016.
13. Asahina, Y.; Manske, R. H. F.; Robinson, R. J. Chem. Soc.
1927, 1708.
Acknowledgements
14. (a) Chang, H. W.; Kim, S. I.; Jung, H.; Jahng, Y. Heterocycles
2003, 60, 1359. (b) Mohanta, P. K.; Kim, K. Tetrahedron Lett.
2002, 43, 3993. (c) Lee, S. H.; Kim, S. I.; Park, J. G.; Lee, E. S.;
Jahng, Y. Hetereocycles 2001, 55, 1555. (d) Kokosi, J.; Szasz,
G.; Hermecz, I. Tetrahedron Lett. 1992, 33, 2995. (e) Lal, B.;
Gidwani, R. M.; De Souza, N. J. Org. Chem. 1990, 55, 5117.
(f) Bergman, J.; Bergman, S. J. Org. Chem. 1985, 50, 1246.
(g) Kaneko, C.; Chiba, T.; Kasai, K.; Miwa, C. Heterocycles
1985, 23, 1385. (h) Mori, M.; Kobayashi, H.; Kimura, M.;
Ban, Y. Heterocycles 1985, 23, 2803. (i) Kokosi, J.; Hermecz,
I.; Podanyi, B.; Szasz, G.; Meszaros, Z. J. Heterocycl. Chem.
1984, 21, 1301. (j) Kokosi, J.; Hermecz, I.; Szasz, G.;
Meszaros, Z. Tetrahedron Lett. 1981, 22, 4861. (k) Danieli, B.;
Palmisano, G. Heterocycles 1978, 9, 803. (l) Kametani, T.;
Chu, V. L.; Higa, T.; Koizumi, M.; Ihara, M.; Fukumoto, K.
J. Am. Chem. Soc. 1977, 99, 2306. (m) Kametani, T.; Figa, T.;
Loc, C. V.; Ihara, M.; Koizumi, M.; Fukumoto, K. J. Am.
Chem. Soc. 1976, 98, 6186, and references cited therein
14a–m.
S. B. M. thanks CSIR, New Delhi, for the award of a
research fellowship. N. P. A. thanks Department of Science
and Technology, New Delhi, for financial support. We thank
Dr. K. N. Ganesh, Head, Division of Organic Chemistry
(Synthesis), for constant encouragement.
References and notes
1. (a) Johne, S.; Groger, D. Pharmazie 1970, 25, 22. (b) Coppola,
G. M. Synthesis 1980, 505. (c) Johne, S. Prog. Drug Res. 1982,
26, 259. (d) Johne, S. Prog. Chem. Org. Nat. Prod. 1984, 46,
159. (e) Michael, J. P. Nat. Prod. Rep. 2000, 17, 603. (f) Witt,
A.; Bergman, J. Curr. Org. Chem. 2003, 7, 659, and references
cited therein 1a–f.
2. (a) Snider, B. B.; Zeng, H. Org. Lett. 2000, 2, 4103. (b) Wang,
H.; Ganesan, A. J. Org. Chem. 2000, 65, 1022. (c) He, F.;
Foxman, B. M.; Snider, B. B. J. Am. Chem. Soc. 1998, 120,
6417.
15. (a) Kar, A.; Argade, N. P. Tetrahedron 2003, 59, 2991. (b) Kar,
A.; Argade, N. P. Tetrahedron Lett. 2002, 43, 6563. (c) Kar,
A.; Argade, N. P. J. Org. Chem. 2002, 67, 7131. (d) Mhaske,
S. B.; Argade, N. P. J. Org. Chem. 2001, 66, 9038.
(e) Mangaleswaran, S.; Argade, N. P. J. Org. Chem. 2001,
66, 5259, and references cited therein 15a–e.
3. Chu, J. H. Sci. Rec. (China) 1951, 4, 279. Chem. Abstr. 1952,
46, 11589b.
4. Li, M. T.; Hung, H. I. Yao Hsueh Pao 1966, 13, 265. Chem.
Abstr. 1966, 65, 3922c.
5. (a) Chen, A. L.; Chen, K. K. J. Am. Pharm. Assoc. 1933, 22,
716. (b) Hsu, H. Y.; Chen, Y. P.; Sheu, S. J.; Hsu, C. H.; Chen,
C. C.; Chang, H. C. Chienese material medica—a concise
guide. Modern Drug: Taipei, 1985; p 288.
16. (a) Johns, S. R.; Lamberton, J. A. Chem. Commun. 1965, 267.
(b) Fitzgerald, J. S.; Johns, S. R.; Lamberton, J. A.; Redcliffe,
A. H. Aust. J. Chem. 1966, 19, 151.
6. Asahina, Y. Acta Phytochim. 1922, 1, 67.
17. (a) Prochazka, M. P.; Eklund, L.; Carlson, R. Acta Chem.
Scand. 1990, 44, 610. (b) Prochazka, M. P.; Carlson, R. Acta
Chem. Scand. 1990, 44, 614.
7. (a) Michael, J. P. Nat. Prod. Rep. 1999, 16, 697. (b) Ikuta, A.;
Urabe, H.; Nakamura, T. J. Nat. Prod. 1998, 61, 1012.
(c) Kamikado, T.; Murakoshi, S.; Tamura, S. Agric. Biol.
Chem. 1978, 42, 1515.