Synthesis of a novel series of highly functionalized Baylis-Hillman adducts of artemisinin with potent anticancer activity

Article abstract of DOI:10.1016/j.tetlet.2013.05.123

A novel series of densely functionalized derivatives of artemisinin have been synthesized using Baylis-Hillman reaction and their further applicability has been demonstrated. The in vitro anticancer activity of these adducts against a panel of human cancer cell lines is summarized. Compound 10 (% GI of 100 against colon colo-205; % GI of 85 against Lung A-549), 7b (% GI of 78 against prostrate PC-3) and 9a, 9b (% GI of 71 against prostrate PC-3) were especially potent in inhibiting the growth of certain human cancer cell lines and were comparable to that of clinically used anticancer drugs. These newly synthesized compounds can be further utilized as potential precursor for the synthesis of libraries of new artemisinin analogs including dimer.

Full text of DOI:10.1016/j.tetlet.2013.05.123

Tetrahedron Letters 54 (2013) 4221–4224
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of a novel series of highly functionalized Baylis–Hillman
adducts of artemisinin with potent anticancer activity
b
b
Abhishek Goswami a, Partha P. Saikia a, Bishwajit Saikia a, Nabin C. Barua a, , Ajit K. Saxena , Nitasha Suri ,
⇑
Madhunika Sharma b, Gakul Baishya a
a Natural Products Chemistry Division, CSIR-North-East Institute of Science & Technology, Jorhat 785006, Assam, India
b Pharmacology Division, CSIR-Indian Institute of Integrative Medicine, Jammu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of densely functionalized derivatives of artemisinin have been synthesized using Baylis–
Hillman reaction and their further applicability has been demonstrated. The in vitro anticancer activity
of these adducts against a panel of human cancer cell lines is summarized. Compound 10 (% GI of 100
against colon colo-205; % GI of 85 against Lung A-549), 7b (% GI of 78 against prostrate PC-3) and 9a,
9b (% GI of 71 against prostrate PC-3) were especially potent in inhibiting the growth of certain human
cancer cell lines and were comparable to that of clinically used anticancer drugs. These newly synthe-
sized compounds can be further utilized as potential precursor for the synthesis of libraries of new arte-
misinin analogs including dimer.
Received 14 March 2013
Revised 24 May 2013
Accepted 28 May 2013
Available online 6 June 2013
Keywords:
Artemisinin
Baylis–Hillman reaction
Cytotoxicity
Ó 2013 Elsevier Ltd. All rights reserved.
Deoxoartemisinin
Artemisinin analogs
Artemisinin 1, a sesquiterpene lactone, isolated from the Chi-
nese medicinal plant Artemisia annua1 and its derivatives, for
example, artemether 2 and arteether 3, are well known antimalar-
ial agents especially against multidrug resistant malarial strains
(Fig. 1). The 1,2,4-trioxane system is primarily responsible for its
antimalarial activity.2 In recent years, anticancer activity of arte-
misinin derivatives has gained attention as a new class of antima-
larial and anticancer agents and several promising leads have also
emerged from these analogs which are in different stages of devel-
opment.3–8
Because of its sensitive nature, the artemisinin molecule offers
very little scope for widespread derivatization. The sensitive nature
of the pharmacophore, that is, 1,2,4-trioxane system also demands
milder reaction conditions for synthetic manipulation. In this con-
text, several authors have attempted functionalization in the deac-
tivated centers of artemisinin using different microorganisms with
limited success, but opened up further prospect of synthetic
manipulation. The first generation derivatives of artemisinin viz.
C-10 ether or ester derivatives having acetal linkage at C-10 posi-
tion have been found to be metabolically unstable in the acidic
environment of the stomach due to acetal linkage and offer limita-
tion to this class of derivatives. As a result, more and more atten-
tion has been diverted to developing C-10 carba analogs to
overcome this problem.
Baylis–Hillman reaction is one of the most important carbon–
carbon bonds forming reaction with enormous synthetic utility,
promise, and potential.9 The Baylis–Hillman adducts contain at
least three functional groups in close proximity which can easily
undergo various transformations through appropriate tuning of
these groups. The adducts can be tailored in different ways to gen-
erate an array of pharmacologically important compounds such as
c
-lactam, c
-butyrolactone, epoxides, azides, etc.10–13 More impor-
tantly, the Michael acceptor14 group present in these adducts offers
further scope for addition of various nucleophiles especially arte-
misinin derived nucleophiles to synthesize artemisinin dimers.
Having known this background and encouraged by the various
reports of enhanced biological activity of 10-deoxo artemisinins,
we were tempted to synthesize some functionalized artemisinin
derivatives utilizing the 10-deoxo artemisinin aldehyde as a
15
H
H
H
5
6
4
7
8
O
O
3
O
O
O
14
O
O
12a
O
O
O
O
12
H
H
H
16
9
10
O
OEt
OMe
O
1
3
2
⇑
Corresponding author. Tel.: +91 376 2371283; fax: +91 376 2370011.
E-mail
addresses:
ncbarua2000@yahoo.co.in,
ncbarua12@rediffmail.com
Figure 1.
(N.C. Barua).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.05.123

4222
A. Goswami et al. / Tetrahedron Letters 54 (2013) 4221–4224
Our synthesis commenced with the three-step conversion of
H
H
H
O
O
artemisinin to 10-b-allyldeoxo artemisinin 4 following the proce-
dure reported by O’Neill.17 It was then converted to the 10-deoxo
artemisinin aldehyde 5 (Scheme 1) employing the one pot route
of dihydroxylation and subsequent cleavage of the diol using os-
mium tetroxide in presence of 2,6-lutidine and sodium periodate
as per procedure reported by Jin and co-workers in 60% yield.18
The aldehyde 5 was treated with a variety of activated olefins in
presence of different bases (Scheme 2) to get hitherto unknown
artemisinin derivatives 6, 7a, 7b, 8, 9a, 9b, and 10. Treatment of
the aldehyde with methyl acrylate in presence of 1, 4-diazabicy-
clo[2.2.2]octane (DABCO) in solvent free condition generated the
adduct 6. Under similar circumstances acrylonitrile furnished ad-
duct 7. In case of cyclohexenone and cyclopentenone, Kim and
co-workers employed 4-dimethylaminopyridine (DMAP) as the
base in catalytic amount.19 We also tried these conditions with
substrate 5 and after 3 days of continuous stirring we could isolate
products 8 and 9 in 50–60% yield. Treatment of methyl vinyl ke-
O
O
Ref 16
a
O
O
O
O
O
O
O
O
O
H
H
H
CHO
5
Artemisinin
4
Scheme 1. Reagents and conditions: (a) osmium tetroxide, 2,6-lutidine, sodium
periodate, dioxane–water (1:1), rt, 2 h, 60%.
precursor. As part of our ongoing project on value addition to phy-
tochemicals,15 we report herein the synthesis of a new series of 10-
deoxo artemisinin derivatives along with their preliminary in vitro
anticancer activity. It is worth mentioning that Baylis–Hillman
reaction on sensitive artemisinin has not been attempted till date.
We designed a series of Baylis–Hillman reaction between
10-deoxo artemisinin aldehyde and different activated olefins in
presence of a suitable base to synthesize highly funtionalized arte-
misinin derivatives. We employed methyl acrylate, acrylonitrile,
cyclohexenone, cyclopentenone, and methyl vinyl ketone as the
activated olefins in this series of reactions to give rise to products
6, 7a, 7b, 8, 9a, 9b, and 10, respectively.16
tone with 5 in presence of imidazole and L-proline furnished an-
other densely functionalized artemisinin analog 10 in 60% yield.20
Two diastereomers were isolated in case of 7 (dr = 1.5:1; 7a:7b)
and 9 (dr = 2:1; 9a:9b)21 unlike the other cases where the other
possible diastereomer was formed in very negligible amount and
we did not isolate them. The major less polar isomer was arbi-
trarily assigned as a-isomer and the minor more polar compound
as the b-isomer.22 Initially, we tried to establish the stereochemis-
try by NOESY experiments. However, because of the flexibility of
the side chain, although we observed indicative NOE cross peaks,
it was not considered conclusive. Therefore, we decided to deter-
mine the stereochemistry by synthesizing the corresponding MTPA
ester. To our surprise, attempts to synthesize MTPA-esters of these
compounds were unsuccessful and hence empirical method of Li-
pase catalyzed kinetic resolution of alcohol put forward by Kazl-
auskas et al.23 was adopted. To assign the absolute configuration
to the carbinol carbon, an equimolar mixture of 7a and 7b was
treated with Pseudomonas fluorescens Lipase from Amino (Lipase
AK) in presence of vinyl acetate (Scheme 3).24 The major less polar
isomer 7a was seen consumed to give acetylated product 11. Since
H
H
H
O
O
O
O
O
O
O
O
O
O
O
O
H
H
H
+
OMe
CN
CN
OH
OH
OH
O
7a (α)
7b (β)
6
b
a
H
O
H
H
O
O
O
O
O
O
H
e
O
O
c
O
O
H
H
O
the a-isomer has (R)-configuration at carbinol carbon, this was in
consonance with empirical rule predicted by Kazlauskas.
OH
O
10
CHO
5
OH O
All the synthesized Baylis–Hillman adducts were tested for
in vitro anticancer activity against different cell lines using Sulfo-
rhodamine B Assay and the results are summarized in Table 1.
Some of the compounds showed encouraging results. Compound
10 showed 100% growth inhibition against colon colo-205 human
cancer cell lines. Similarly, the same compound is also found to
be promising against lung cancer cells of A-549 type, prostrate
PC-3, and neuroblastoma IMR-32 to an extent of 85, 81, and 79
(% GI) respectively. Among other compounds, 7b showed glimpses
of good activity against prostrate PC-3 (% GI 78) and lung A-549
(% GI 77). Appreciable anticancer activities were also shown by
9b against lung A-549 (% GI 70) and prostrate PC-3 (% GI 71).
The Michael acceptor groups present in these adducts make
them susceptible to be attacked by nucleophiles such as nitro
8
d
H
H
O
O
O
O
O
O
O
O
H
H
+
O
O
OH
OH
9b (β)
9a (α)
Scheme 2. Reagents and conditions: (a) methyl acrylate, DABCO, 31%; (b) acrylo-
nitrile, DABCO, 67%; (c) cylohexenone, DMAP, THF–water, 51%; (d) cyclopentenone,
DMAP, THF–water, 60%; (e) methyl vinyl ketone, imidazole,
60%.
L
-proline, THF–water,
H
H
H
H
O
O
O
O
O
O
O
O
O
O
O
Lipase AK, Vinyl acetate
O
O
H
H
+
+
H
H
O
DCM
O
O
CN
CN
CN
CN
OH
OH
7b
OAc
OH
7b
11
7a
Scheme 3.

A. Goswami et al. / Tetrahedron Letters 54 (2013) 4221–4224
4223
Table 1
Proliferation inhibition assay against different cancer cell lines
Compounds
Lung
Ovary
Prostrate
DU-145
Neuroblastoma
IMR-32
Breast
MCF-7
Colon
Concd (M)
A-549
IGR-OV-1
PC-3
Colo-205
% Growth inhibition
6
5 ꢂ 10ꢁ5
5 ꢂ 10ꢁ5
5 ꢂ 10ꢁ5
5 ꢂ 10ꢁ5
5 ꢂ 10ꢁ5
5 ꢂ 10ꢁ5
5 ꢂ 10ꢁ5
2 ꢂ 10ꢁ5
1 ꢂ 10ꢁ5
1 ꢂ 10ꢁ5
1 ꢂ 10ꢁ6
5 ꢂ 10ꢁ5
70
66
77
66
68
70
85
—
63
42
56
60
54
52
33
—
—
—
—
26
—
—
56
48
62
72
66
57
79
—
—
—
70
23
—
—
7a (a)
46
60
52
47
41
73
—
—
92
—
65
78
68
71
71
81
—
—
54
—
46
55
43
51
40
66
—
—
—
72
45
56
75
63
63
50
100
54
—
7b (b)
8
9a (a)
9b (b)
10
Fluorouracil
Paclitaxel
Mitomycin
Adriamycin
Artemisinin
69
—
—
—
—
40
29
38
22
‘–‘ Indicates that these compounds were not tested against those cell lines.
10. Masuyama, Y.; Nimura, Y.; Kurusu, Y. Tetrahedron Lett. 1991, 32, 225.
11. (a) Bailey, M.; Marko, I. E.; Ollis, W. D. Tetrahedron Lett. 1991, 32, 2687; (b)
Jackson, R. F. W.; Standen, S. P.; Clegg, W.; McCamley, A. Tetrahedron Lett. 1992,
33, 6197.
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13. Basavaiah, D.; Rao, J. S. Tetrahedron Lett. 2004, 45, 1621.
H
H
O
O
CH3NO2
Amberlyst-A 21
O
O
O
O
O
O
H
H
NO2
CN
14. (a) Kupchan, S. M.; Eakin, M. A.; Thomas, A. M. J. Med. Chem. 1971, 14, 114; (b)
Yanagita, M.; Inayama, S.; Kawamata, T.; Ohkura, T.; Herz, W. Tetrahedron Lett.
1969, 4170; (c) Kawamata, T.; Inayama, S. Chem. Pharm. Bull. 1971, 19, 643; (d)
Inayama, S.; Harimaya, K.; Shimizu, N.; Hori, H.; Ohkura, T.; Kawamata, T.;
Iitaka, Y. Heterocycles 1985, 23, 377; (e) Hall, I. H.; William, W. L., Jr.; Grippo, A.
A.; Lee, K. H.; Holbrook, D. J.; Chaney, S. G. Anticancer Res. 1988, 8, 33.
15. Goswami, A.; Saikia, P. P.; Barua, N. C.; Bordoloi, M. J.; Yadav, A.; Bora, T. C.;
Gogoi, B. K.; Saxena, A. K.; Suri, N.; Sharma, M. Bioorg. Med. Chem. Lett. 2010, 20,
359.
16. (a) Baishya, G.; Barua, N. C.; Goswami, A.; Saikia, P. P.; Rao, P. G.; Saxena, A. K.;
Suri, N.; Sharma, M. Patent Filed, 0127DEL2010.; (b) Saikia Bishwajit; Barua
Nabin C.; Saikia Partha P.; Goswami Abhishek; Rao Paruchuri G.; Saxena Ajit K.;
Suri Nitasha Patent filed, 0366DEL2011 for India & PCT/IN2012/000099.
17. Jeyadevan, J.; Bray, P. G.; Chadwick, J.; Mercer, A. E.; Bryne, A.; Ward, S. A.; Park,
B. K.; Williams, D. P.; Cosstick, R.; Davies, J.; Higson, A. P.; Irving, E.; Posner, G.
H.; O’Neill, P. M. J. Med. Chem. 2004, 47, 1290.
18. Yu, W.; Mei, Y.; Kang, Y.; Hua, Z.; Jin, Z. Org. Lett. 2004, 6, 3217.
19. Lee, K. Y.; Gong, J. H.; Kim, J. N. Bull. Korean Chem. Soc. 2002, 23, 659.
20. Shi, M.; Jiang, J.-K.; Li, C.-Q. Tetrahedron Lett. 2002, 43, 127.
21. Diastereomeric ratio was determined from NMR spectra.
22. Ma, J.; Katz, E.; Kyle, D. E.; Ziffer, H. J. Med. Chem. 2000, 43, 4228.
23. (a) Kazlauskas, R. J.; Weissfloch, A. N. E.; Rappaport, A. T.; Cuccia, L. A. J. Org.
Chem. 1991, 56, 2656; (b) Weissfloch, A. N. E.; Kazlauskas, R. J. J. Org. Chem.
1995, 60, 6959; (c) Burges, K.; Jennings, L. D. J. Am. Chem. Soc. 1991, 113, 6129;
(d) Kim, M.-J.; Cho, H. J. J. Chem. Soc., Chem. Commun. 1992, 1411; (e) Szigeti,
M.; Toke, E. R.; Turóczi, M. C.; Nagy, V.; Szakács, G.; Poppe, L. Arkivoc 2008, III,
54.
CN
OH
7a
OH
13
Scheme 4.
stabilized carbanion, thiol, amine etc. To validate the probable syn-
thetic routes, Michael addition of nitromethane to 7a was carried
out in presence of Amberlyst A-21 to generate 13 in 80% yield
(Scheme 4).
In conclusion, we have synthesized25 a novel series of artemis-
inin derivatives using Baylis–Hillman reaction on 10-deoxo arte-
misinin aldehyde and demonstrated its further applications by
1,4-addition of nitromethane to the Michael acceptor substructure.
Further work in this direction is in progress in our laboratory and
will be reported in due course of time.
Acknowledgments
We would like to thank Director, NEIST, Jorhat for providing
necessary facilities to carry out this work. A.G. thanks UGC and
B.S. thank CSIR-New Delhi for the award of fellowship. This is an
outcome of CSIR network project NWP-0009.
24. Borah, J. C.; Boruwa, J.; Kalita, B.; Hazarika, A. K.; Barua, N. C. Indian J. Chem.
1961, 2005, 44B.
25. Selected analytical data for unknown compounds: Compound 6 (0.120 g, 31%) as
gummy liquid. Rf = 0.2 (1:4 EtOAc/hexane); ½a D20
ꢀ
(c 1, CHCl3) +69.5; IR (CHCl3) m
1715, 3458, 2950 cmꢁ1 1H NMR (CDCl3, 300 MHz) d 0.82 (d, J = 7.4 Hz, 3H, 6-
;
References and notes
Me), 0.95 (d, J = 5.3 Hz, 3H, 9-Me), 1.41 (s, 3H, 3-Me), 2.20–2.07 (m, 12H, arte
aliphatic), 2.33 (dt, J = 3.4, 12.4 Hz, 1H), 2.65 (sextet, 1H), 3.33 (d, J = 7.0 Hz,
1H), 3.77 (s, 3H), 4.48 (m, 1H, H-10), 4.77 (br s, 1H), 5.36 (s, 1H, H-12), 6.02 (s,
1H, C@CH2), 6.33 (s, 1H, C@CH2); 13C NMR (CDCl3, 75 MHz) 12.7, 19.9, 24.3,
24.4, 25.7, 29.6, 33.9, 34.0, 36.2, 37.1, 44.0, 51.5, 51.9, 68.5, 71.6, 80.6, 88.6,
103.0, 125.3, 141.8, 166.4; ESIMS m/z 396.2 (M+); [found: C, 63.53; H, 8.21.
1. Klaymann, D. L. ACS Symp. Ser. 1993, 534, 242.
2. (a) Klayman, D. L. Science 1985, 228, 1049; (b) China Co-operative Research
Group on Qinghaosu and its Derivatives as Antimalarials J. Tradit. Chin. Med.
1982, 2, 9.
3. Saikia, B.; Saikia, P. P.; Goswami, A.; Barua, N. C.; Saxena, A. K.; Suri, N. Synthesis
2011, 19, 3173.
C
21H32O7 calcd C, 63.62; H, 8.14].
Compound 7a (
CHCl3) +13.2, IR (CHCl3)
a
): solid, mp = 137 °C, Rf = 0.4 (1:3 EtOAc/hexane), ½a D20
ꢀ
(c 1.1,
m ;
3469, 2926 cmꢁ1 1H NMR (CDCl3, 300 MHz) d 0.88
4. (a) Li, Y.; Shan, F.; Wu, J. M.; Wu, G. S.; Ding, J.; Xiao, D.; Yang, W. Y.; Atassi, G.;
Le’once, S.; Caignard, D. H.; Renard, P. Bioorg. Med. Chem. Lett. 2001, 11, 5; (b)
Yang, Z. S.; Zhou, W. L.; Sui, Y.; Wang, J. X.; Wu, J. M.; Zhou, Y.; Zhang, Y.; P. He,
L.; Han, J. Y.; Tang, W.; Zuo, J. P.; Li, Y. J. Med. Chem. 2005, 48, 4608.
5. Yang, Z. S.; Wang, J. X.; Zhou, Y.; Zuo, J. P.; Li, Y. Bioorg. Med. Chem. 2006, 14,
8043.
6. Slade, D.; Galal, A. M.; Gul, W.; Radwan, M. M.; Ahmed, S. A.; Khan, S. I.;
Tekwani, B. L.; Jacob, M. R.; Ross, S. A.; ElSohly, M. A. Bioorg. Med. Chem. 2009,
17, 7949.
7. Jung, M.; Park, N.; Moon, H.-I.; Lee, Y.; Chung, W.-Y.; Park, K.-K. Bioorg. Med.
Chem. Lett. 2009, 19, 6303.
8. Chaturvedi, D.; Goswami, A.; Saikia, P. P.; Barua, N. C.; Rao, P. G. Chem. Soc. Rev.
2010, 39, 435.
(d, J = 7.4 Hz, 3H, 6-Me), 0.96 (d, J = 4.2 Hz, 3H, 9-Me), 1.40 (s, 3H, 3-Me), 1.15–
2.07 (m, 12H, arte aliphatic), 2.32 (dt, J = 3.4, 12.4 Hz, 1H), 2.66 (sextet, 1H),
4.38 (br s, 1H, OH), 4.45 (m, 1H), 4.66 (m, 1H), 5.37 (s, 1H, H-12), 6.00 (s, 1H,
C@CH2), 6.14 (s, 1H, C@CH2); 13C NMR (CDCl3, 75 MHz) 11.6, 12.4, 20.0, 24.7,
25.9, 30.6, 35.5, 36.4, 37.5, 43.4, 51.7, 73.1, 74.8, 80.9, 89.6, 103.1, 125.7, 129.9,
144.1, 188.2; ESIMS: m/z 386.3 (M++Na); [found: C, 66.12; H, 8.07; N, 3.81.
C
20H29NO5 calcd C, 66.09; H, 8.04; N, 3.85].
Compound 7b (b): Gummy, Rf = 0.3 (1:3 EtOAc/hexane) ½a D20
ꢀ
(c 1.0, CHCl3)
+33.0, IR (CHCl3)
m ,
3468, 2925 cmꢁ1 1H NMR (CDCl3, 300 MHz) d 0.87 (d,
J = 7.4 Hz, 3H, 6-Me), 0.96 (d, J = 5.2 Hz, 3H, 9-Me), 1.66 (s, 3H, 3-Me), 1.25–
2.17 (m, 12H, arte aliphatic), 2.32 (dt, J = 3.4, 12.4 Hz, 1H), 2.66 (sextet, 1H),
3.63 (br s, 1H, OH), 4.59 (m, 2H), 5.37 (s, 1H, H-12), 6.09 (s, 1H, C@CH2), 6.24 (s,
1H, C@CH2); 13C NMR (CDCl3, 75 MHz) d 12.7, 20.1, 24.7, 25.9, 30.0, 33.3, 34.2,
36.5, 37.5, 43.8, 51.9, 70.0, 70.9, 80.8, 89.3, 103.2, 122.0, 130.5, 133.0, 190.5;
9. (a) Basavaiah, D.; Rao, A. J.; Satyanrayana, T. Chem. Rev. 2003, 103, 811; (b)
Basavaiah, D.; Reddy, B. S.; Badsara, S. S. Chem. Rev. 2010, 110, 5447; (c)
Basavaiah, D.; Rao, K. V.; Reddy, R. J. Chem. Soc. Rev. 2007, 36, 1581.

4224
A. Goswami et al. / Tetrahedron Letters 54 (2013) 4221–4224
ESIMS: m/z 363.2 (M+); [found: C, 66.15; H, 8.07; N, 3.79. C20H29NO5 calcd C,
(M+); [found: C, 67.31; H, 8.24. C22H32O6 calcd C, 67.32; H, 8.22].
66.09; H, 8.04; N, 3.85].
Compound 10: Rf = 0.45 (1:2 EtOAc/hexane); ½a D20
ꢀ
(c 0.45, CHCl3) +14.4; IR
Compound 8: Solid, Rf = 0.6 (1:3 EtOAc/hexane) mp = 134 °C, ½a D20
ꢀ
(c 1.1, CHCl3)
(neat) m ;
1717, 2923, 3481 cmꢁ1 1H NMR (CDCl3, 300 MHz) d 0.74 (d, J = 7.1 Hz,
ꢁ3.4; IR (CHCl3)
m
1726, 2924, 3495 cmꢁ1
;
1H NMR (CDCl3, 300 MHz) d 0.92 (d,
3H, 6-Me), 0.95 (d, J = 6.0 Hz, 3H, 9-Me), 1.38 (s, 3H, 3-Me), 1.20–2.20 (m, 13H,
arte aliphatic), 2.31 (m, 1H), 2.36 (s, 3H, –CH3), 3.77 (t, J = 6.5 Hz, 1H, CH2–
CHOH), 4.49 (br s, 1H, –OH), 4.78 (d, J = 9.0 Hz, 1H, CH2–CHOH), 5.29 (s, 1H, H-
12), 6.18 (s, 1H, C@CH2), 6.30 (s, 1H, C@CH2); 13C NMR (CDCl3, 75 MHz): d 13.6,
20.2, 21.2, 24.7, 25.9, 28.4, 29.5, 30.0, 34.0, 36.1, 37.3, 45.9, 51.7, 75, 80.5, 91.8,
104.7, 122, 188.2, 204.5; ESIMS: m/z 380.2 (M+); [found: C, 66.31; H, 8.43.
J = 7.3 Hz, 3H, 6-Me), 0.95 (d, J = 6.2 Hz, 3H, 9-Me), 1.39 (s, 3H, 3-Me), 1.23–
2.04 (m, 15H, arte aliphatic), 2.39–2.43 (m, 3H), 2.68 (m, 1H, H-9), 3.72 (m, 1H,
CH2–CHOH), 4.13 (q, J = 7.1 Hz, 1H, H-10), 4.27 (br s, 1H, CH2–CHOH), 4.99 (d,
J = 9.8 Hz, 1H, CH-OH), 5.23 (s, 1H, H-12), 7.18 (t, J = 3.8 Hz, 1H, C@CH); 13C
NMR (CDCl3, 75 MHz) d 13.5, 20.2, 21.2, 22.8, 24.8, 25.7, 26.0, 29.5, 34.1, 36.0,
37.4, 38.0, 38.6, 45.8, 51.6, 65.4, 73.9, 80.8, 91.8, 104.4, 141.3, 145.6, 199.3;
ESIMS m/z 406.2 (M+); [found: C, 67.92; H, 8.39. C23H34O6 calcd C, 67.96; H,
8.43].
C
21H32O6 calcd C, 66.29; H, 8.48].
Compound 11: as a gum in 40% yield. IR (CHCl3)
m
1731, 3469, 2926 cmꢁ1 1H
;
NMR (CDCl3, 300 MHz) d 0.91 (d, J = 7.4 Hz, 3H, 6-Me), 0.96 (d, J = 4.2 Hz, 3H, 9-
Me), 1.42 (s, 3H, 3-Me), 1.18–2.17 (m, 12H, arte aliphatic), 2.1 (s, 3H, CH3), 2.32
(dt, J = 3.4, 12.4 Hz, 1H), 2.68 (sextet, 1H), 4.41 (br s, 1H, OH), 4.46 (m, 1H), 4.71
(m, 1H), 5.37 (s, 1H, H-12), 6.04 (s, 1H, C@CH2), 6.11 (s, 1H, C@CH2); 13C NMR
(CDCl3, 75 MHz) 11.6, 12.4, 20.0, 24.7, 25.9, 30.6, 35.5, 36.4, 37.5, 43.4, 51.7,
73.1, 74.8, 80.9, 89.6, 103.1, 125.7, 129.9, 144.1, 171.2, 188.2; ESIMS: m/z 405.2
(M+); [found: C, 65.12; H, 7.74; N, 3.51. C22H31NO6 calcd C, 65.17; H, 7.71; N,
3.45].
Compound 9a (
ꢁ17.1; IR (CHCl3)
a
): Gummy; Rf = 0.5 (1:3 EtOAc/hexane); ½a D20
ꢀ
(c 0.5, CHCl3)
m
1726, 2918, 3469 cmꢁ1 1H NMR (CDCl3, 300 MHz) d 0.89
;
(d, J = 7.1 Hz, 3H, 6-Me), 0.91 (d, J = 5.8 Hz, 3H, 9-Me), 1.39 (s, 3H, 3-Me), 1.25–
2.03 (m, 13H, arte aliphatic), 2.17–2.42 (m, 3H), 2.43–2.60 (m, 2H), 3.75 (m,
1H), 4.27 (m, 1H, CH2–CHOH), 4.88 (d, J = 9.3 Hz, 1H, CH2-CHOH), 5.23 (s, 1H,
H-12), 7.65 (s, 1H, C@CH); 13C NMR (CDCl3, 75 MHz) d 13.6, 20.2, 21.2, 24.7,
26.0, 26.5, 29.6, 34.1, 35.5, 36.0, 36.7, 37.4, 45.7, 51.6, 64.5, 73.7, 80.8, 91.8,
104.4, 148.5, 158.5, 208.9; ESIMS: m/z 415.8 (M++Na); [found: C, 67.28; H, 8.19.
Compound 13: (0.093 g, 80%) as gum. Rf = 0.3 (1:2 EtOAc/hexane); ½a D20
ꢀ
(c 2.5,
C
22H32O6 calcd C, 67.32; H, 8.22].
CHCl3) +29.1; IR (CHCl3) m ;
3469, 2926, 1556 cmꢁ1 1H NMR (CDCl3, 300 MHz) d
Compound 9b (b): Gummy, Rf = 0.4 (1:3 EtOAc/hexane); ½a D20
ꢀ
(c 0.7, CHCl3)
0.90 (d, J = 7.5 Hz, 3H, 6-Me), 0.98 (d, J = 5.2 Hz, 3H, 9-Me), 1.40 (s, 3H, 3-Me),
1.25–2.03 (m, 14H, arte aliphatic), 2.31 (m, 1H), 2.58 (dt, J = 7.1, 14.0 Hz, 1H),
2.83 (sextet, 1H), 3.98 (m, 1H, H-10), 4.42 (br s, 1H, OH), 4.58–4.70 (m, 3H,
CH2–CHOH+CH2NO2), 5.35 (s, 1H, H-12). 13C NMR (CDCl3, 75 MHz): d 12.3,
20.2, 24.8, 25.8, 26.0, 32.8, 34.2, 35.9, 36.3, 37.2, 37.4, 43.3, 51.7, 72.8, 74.5,
80.9, 91.7, 104.5, 119.0; ESIMS: m/z 424.2 (M+); [found: C, 59.47; H, 7.56; N,
6.64. C21H32N2O7 calcd C, 59.42; H, 7.60; N, 6.60].
+22.7; IR (CHCl3) m ;
1696, 2918, 3436 cmꢁ1 1H NMR (CDCl3, 300 MHz) d 0.84 (d,
J = 7.3 Hz, 3H, 6-Me), 0.91 (d, J = 5.8 Hz, 3H, 9-Me), 1.39 (s, 3H, 3-Me), 1.25–
2.16 (m, 13H, arte aliphatic), 2.30 (dt, J = 3.4, 12.4 Hz, 1H), 2.44 (m, 1H), 2.61–
2.67 (m, 3H), 3.41 (d, J = 6.1 Hz, 1H, CH2–CHOH), 4.36–4.41 (m, 1H, H-10), 4.72
(br s, 1H, CH2–CHOH), 5.37 (s, 1H, H-12), 7.63 (s, 1H, C@CH); 13C NMR (CDCl3,
75 MHz) d 14.0, 20.2, 21.9, 24.6, 26.0, 26.5, 29.9, 34.2, 35.1, 35.6, 36.5, 37.4,
46.2, 52.3, 66.4, 72.2, 81.0, 95.9, 103.4, 148.0, 159.0, 208.8; ESIMS: m/z 392.2