Chemical and biological explorations of the electrophilic reactivity of the bioactive marine natural product halenaquinone with biomimetic nucleophiles

Article abstract of DOI:10.1016/j.bmcl.2010.12.056

The electrophilic reactivity of the bioactive marine sponge natural product halenaquinone has been investigated by reaction with the biomimetic nucleophiles N-acetyl-l-cysteine and N_α-acetyl-l-lysine. While cysteine reacted at the vacant quinon

Full text of DOI:10.1016/j.bmcl.2010.12.056

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1261–1264
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Chemical and biological explorations of the electrophilic reactivity
of the bioactive marine natural product halenaquinone with biomimetic
nucleophiles
Jiayi Wang a, Marie-Lise Bourguet-Kondracki b, Arlette Longeon b, Joëlle Dubois c, Alexis Valentin d,
Brent R. Copp a,
⇑
a Department of Chemistry, University of Auckland, Private Bag 92019, Auckland, New Zealand
b Laboratoire des Molécules de Communication et Adaptation des Micro-organismes, FRE 3206 CNRS, Muséum National d’Histoire Naturelle, 57 rue Cuvier (C.P. 54),
75005 Paris, France
c Institut de Chimie des Substances Naturelles, CNRS UPR 2301, Centre de Recherche de Gif, Avenue de la Terrasse, 91198 Gif sur Yvette Cedex, France
d Pharmacochimie des Substances Naturelles et Pharmacophores Redox, UMR 152 IRD-UPS, Université Paul Sabatier, Faculté de Pharmacie, 35 Chemin des Maraîchers,
31062 Toulouse Cedex 4, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The electrophilic reactivity of the bioactive marine sponge natural product halenaquinone has been
investigated by reaction with the biomimetic nucleophiles N-acetyl-L-cysteine and N -acetyl-L-lysine.
a
While cysteine reacted at the vacant quinone positions C-14 and C-15, lysine was found to react prefer-
entially at the keto-furan position C-1. A small library of analogues was prepared by reaction of
halenaquinone with primary amines, and evaluated against a range of biological targets including phos-
pholipase A2, farnesyltransferases (FTases) and Plasmodium falciparum. Geranylamine analogue 11 exhib-
Received 10 November 2010
Accepted 13 December 2010
Available online 16 December 2010
Keywords:
Marine natural product
Electrophilic
ited the most potent activity towards FTases (IC50 0.017–0.031 lM) and malaria (IC50 0.53–0.62 lM).
Ó 2010 Elsevier Ltd. All rights reserved.
PLA2
Farnesyltransferase
Plasmodium falciparum
Halenaquinone (1)1 and xestoquinone (2)2 were the first
examples of a now large family of polycyclic aromatic natural
products isolated from marine sponges of the genera Xestospongia,
Neopetrosia and Adocia.3 While halenaquinone was originally
reported to exhibit antibacterial properties, subsequent studies
revealed it also to be a potent irreversible inhibitor of phosphatidyl-
(3).9 As part of our ongoing investigation of bioactive natural
products isolated from South Pacific marine sponges, we recently
identified orhalquinone (4) as an inhibitor of bee venom phospholi-
pase A2 and human and yeast farnesyltransferase enzymes and a
growth inhibitor of P. falciparum.3n Comparative biological evalua-
tion with halenaquinone identified that loss of the C-1 electrophilic
center was detrimental to PLA2 inhibition, but was requisite for
in vitro antimalarial activity. Our isolation of orhalquinone (4) from
Xestospongia sp. also yielded considerable quantity of halenaqui-
none (1),10 which provided an opportunity to investigate the reac-
tivity of the natural product with biomimetic-type thiol and amine
nucleophiles, which in turn led to the preparation and biological
evaluation of a library of novel amine analogues. In this letter, we
present the results of these studies.
inositol 3-kinase (PI3-kinase)4 and protein tyrosine kinase.3d,5
A
number of research groups have noted differing biological activities,
and potency of activity, between halenaquinone (1) and xestoqui-
none (2), despite the only structural difference between the com-
pounds being oxidation at C-3. For example, halenaquinone is a
more potent PI3-kinase4 and protein tyrosine kinase3d,5 inhibitor
and more potent growth inhibitor of fungi,6 while xestoquinone is
a more potent cytotoxin6 and a stronger growth inhibitor of Plasmo-
dium falciparum.7,3n Both 1 and 2 contain a para-quinone moiety, the
electrophilic nature of which has been confirmed in the case of 2 by
formation of a di(2-mercaptoethanol) adduct.8 The 3-ketofuran
fragment of halenaquinone (1) is also expected to be electrophilic
(at C-1),3d being reminiscent of a similar substructural fragment in
the irreversibly PI3-kinase inhibiting natural product wortmannin
Reaction of halenaquinone with N-acetyl-L-cysteine (1 equiv) in
DMF and triethylamine (1 equiv) for 3 h yielded a mixture of unre-
acted halenaquinone and a new product 5 (2:1 ratio) as judged by
1H NMR spectroscopy.11 While many of the resonances of the two
compounds were overlapped, quinonoid proton H-15 (dH 6.93, s)
and furan proton H-1 (dH 8.78, s) of the new derivative were dis-
tinct, allowing characterization of 5. Inspection of 1H, 13C and HSQC
NMR data observed for 5 indicated loss of one of the two chemi-
cally equivalent quinonoid proton resonances of halenaquinone
and the presence of an intact furan ring (dH 8.78, dC 151.8), suggest-
⇑
Corresponding author. Tel.: +64 9 373 7599; fax: +64 9 373 7422.
E-mail address: b.copp@auckland.ac.nz (B.R. Copp).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.12.056

1262
J. Wang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1261–1264
The selectivity of reaction between amines and halenaquinone
at the C-1 position was further explored. While reaction of
halenaquinone with secondary amines yielded complex mixtures
of products (data not shown), primary amines afforded single
products that were stable to chromatographic purification (Scheme
1).14 Reaction of halenaquinone with phenethylamine (1 equiv) in
CH2Cl2 in the presence of triethylamine for 1 h followed by purifi-
cation via silica gel flash chromatography yielded halenaquinone
analogue 8 in 99% yield.15 As observed previously for lysine
analogue 7, analysis of 1H and 13C NMR data acquired for 8
established the presence of resonances attributable to H-14/15
and C-14/15 and the absence of furan ring resonances. A COSY
NMR spectrum established spin-system connectivity from the
phenethylamine methylene protons (dH 3.69, 3.62, m, H2-21; dH
2.97, m, H2-22) to an exchangeable proton (dH 11.68, dt, J = 6.5,
13.2 Hz, NH) to a resonance at dH 8.42 (1H, d, J = 13.2 Hz, H-1).
HMBC NMR correlations observed for the dH 8.42 resonance to
C-21 (dC 51.9) and C-3 (dC 195.1) placed this proton at C-1. An addi-
tional HMBC correlation observed between the H2-21 (dH 3.69 and
3.62) resonances and C-1 (dC 160.5) further confirmed the struc-
ture of 8. A J-HMBC NMR experiment16 determined the heteronu-
clear coupling constant between C-3 and H-1 to be 7.5 Hz,
indicative of a trans H-1/C-3 geometry and a D1 Z configuration.17
Following this general protocol, reaction of halenaquinone with
n-pentylamine, tert-butoxycarbonyl ethylenediamine, geranyl-
amine and glycine methylester afforded analogues 9 (93% yield),18
10 (78%),19 11 (78%)20 and 12 (77%).21 Analysis of 1H and 13C
one-dimensional and two-dimensional NMR data and mass
spectrometric data was used to confirm the structures of 9–12.
Compounds 8–12 were evaluated for activity against bee venom
phospholipase A2, yeast (Saccharomyces cerevisiae) and human
protein farnesyltransferases, FcB1 and 3D7 strains of P. falciparum
and VERO cells. The results from the in vitro assays are presented
ing thiol attack at C-14 or C-15 of 1. HMBC NMR correlations ob-
served between H-11 (dH 8.69) and C-17 (dC 135.0) and between
the remaining quinonoid proton resonance (dH 6.93, s) and C-17
established the identity of
5
as 14-(N-acetyl-L-cysteinyl)-
halenaquinone. Extended reaction of halenaquinone with excess
N-acetyl-L-cysteine (P5 equiv) yielded an unstable product that
was characterized as the 14,15-dicysteinyl compound 6.12 Thus
the reactivity of halenaquinone towards thiol nucleophiles mirrors
that observed for xestoquinone,8 in that the reactive centers are
C-14 and C-15 of the quinone ring.
Reaction of halenaquinone with N -acetyl-L-lysine (5 equiv) in a
a
mixed solvent system (DMSO/MeOH/H2O, 1:1:0.1) for 1 hr yielded
an unstable single product 7.13 Mass spectrometry indicated the
product to be a mono-N-acetyllysine adduct of halenaquinone
((+)-ESIMS m/z 521.1921 MH+, calcd for C28H29N2O8, 521.1918).
Analysis of 1H, 13C and 2-D NMR data established the presence of
H-14 and H-15 resonances (dH 7.13, 2H, s) and the absence of res-
onances associated with the furan moiety of halenaquinone. The
sharp H-1 (dH 8.90, s) resonance of halenaquinone was noticeably
absent from the 1H NMR spectrum of 7, being replaced by an
olefinic methine at dH 8.47 (1H, br d, J = 12.9 Hz, H-1), which in
an HMBC spectrum correlated weakly to an sp2 resonance at dC
194.0 (C-3). From the COSY NMR spectrum, connectivity between
the acetyllysine N H resonance (dH 11.48, br m) and dH 8.47
e
(H-1) was observed, establishing the covalent linkage between
the two reactants. Instability of the product prevented conclusive
determination of the geometry of
below) suggest it to be Z as shown. Further reaction of halenaqui-
none with 10-fold excess of N -acetyl- -lysine afforded a complex
D
1, but subsequent studies (see
L
a
mixture of products, (À)-ESI mass spectrometric analysis of which
detected an ion at m/z 705.2761 [MÀH]À, consistent with the pres-
ence of a di(N -acetyl-L-lysine)halenaquinone adduct (calcd for
a
C36H41N4O11, 705.2777). Thus in contrast to the reactivity towards
thiol nucleophiles, amines preferentially attack halenaquinone at
C-1.
Scheme 1. Semisynthesis of 8–12 from halenaquinone (1).

J. Wang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1261–1264
1263
Table 1
Biological activities of halenaquinone (1), orhalquinone (4) and derivatives 8–12
a
Compound
PLA2
yFTaseb
hFTasec
Pf-FcB1d
Pf-3D7e
VEROf
Halenaquinone 1g
3.7 0.3
1.6 0.1
0.93 0.18
0.41 0.03
0.44 0.03
0.057 0.004
nt
>30
>30
>60
>62
Orhalquinone 4g
1570 92.6
17.7 0.4
23.9 2.6
12.8 0.8
34.4 3.7
76.8 11.0
0.40 0.01
0.31 0.04
0.041 0.004
nth
0.017 0.001
nt
9.2 0.4
8.8 0.3
9.2 1.2
52.8 14.4
0.62 0.25
55.8 21.8
10.9 0.3
2.1 0.8
7.4 1.7
nt
0.53 0.12
16.5 6.2
8
9
10
11
12
4.7 2.0
6.3 1.5
7.4 0.2
8.6 1.6
13.4 7.2
0.031 0.003
nt
a
Bee venom PLA2. IC50 values (
Farnesyltransferase from the yeast Saccharomyces cerevisiae. IC50 values (
l
M
SEM; n = 2). Manoalide (positive control) IC50 0.5 0.05
lM. Assay protocol is described in Ref. 3n.
b
lM
SEM; n = 4). FTase inhibitor I (positive control) IC50 0.032
l
M. Assay protocol is described in
Ref. 3n.
c
Farnesyltransferase from human. IC50 values (
Plasmodium falciparum strain FcB1 (chloroquine resistant). IC50 values (
l
M
SEM; n = 4). FTI-276 (positive control) IC50 0.015 lM. Assay protocol is described in Ref. 3n.
d
l
M
SEM; n = 2). Highest concentration tested 10
l
g/mL. Chloroquine (positive control) IC50
g/mL. Chloroquine (positive control) IC50
M. Highest concentration tested 20 g/mL.
150 nM. Assay protocol is described in Ref. 3n.
e
Plasmodium falciparum strain 3D7 (chloroquine sensitive). IC50 values (
lM
SEM; n = 2). Highest concentration tested 10 l
30 nM. Assay protocol is described in Ref. 3n.
f
VERO mammalian non-malignant cell line. IC50 values (
lM
SEM; n = 2). Doxorubicin (positive control) IC50 5.12 0.17
l
l
Assay protocol is described in Ref. 3n
g
Data taken from Ref. 3n.
Not tested.
h
in Table 1. We have previously reported that while halenaquinone
(1) is a micromolar inhibitor of PLA2, the furan ring-opened natural
product orhalquinone (4) and halenaquinol sulfate (13) are signif-
icantly less potent (IC50 >1 mM).3n All of 8–12 were found to be
modest inhibitors of PLA2 enzymatic activity, with IC50 values of
and also demonstrated that the electrophilic center at C-1 of the
natural product is not a necessary requirement for activity. The
ability to functionalize the halenaquinone scaffold selectively at
either C-14/C-15 or C-1 by the judicious choice of linker chemistry
will facilitate biotinylation22 or click chemistry23 activity-based
protein profiling experiments to identify cellular targets24 of this
intriguing marine natural product.
12.8–76.8 lM. Taking the poor biological activities of 4 and 13 to-
wards PLA2 into account, these current results indicate the impor-
tance of the presence of a quinone ring and oxygen functionality at
C-3, but not the presence of an electrophilic center at C-1, for PLA2
inhibition.
Acknowledgments
This work was initiated thanks to the CRISP (Coral Reef Initia-
tive in the South Pacific) project granted by the Agence Française
de Développement. The authors also thank the University of
Auckland for support of this research.
References and notes
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amine analogue 11 being particularly potent (IC50 0.017 and
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Org. Chem. 1993, 58, 4871; (e) Harada, N.; Sugioka, T.; Uda, H.; Kuriki, T.;
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Kelly-Borges, M.; Scheuer, P. J. Heterocycles 1998, 49, 355; (h) Cao, S.; Foster, C.;
Brisson, M.; Lazlo, J. S.; Kingston, D. G. I. Bioorg. Med. Chem. 2005, 13, 999; (i) De
Almeida Leone, P.; Carroll, A. R.; Towerzey, L.; King, G.; McArdle, B. M.; Kern, G.;
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Kubota, T.; Kon, Y.; Kobayashi, J. Heterocycles 2008, 76, 1571; (l) Millan-
Aguinaga, N.; Soria-Mercado, I. E.; Williams, P. Tetrahedron Lett. 2010, 51, 751;
(m) Dai, J.; Sorribas, A.; Yoshida, W. Y.; Kelly, M.; Williams, P. G. Journal. Nat.
Prod. 2010, 73, 1188; (n) Longeon, A.; Copp, B. R.; Roue, M.; Dubois, J.; Valentin,
A.; Petek, S.; Debitus, C.; Bourguet-Kondracki, M.-L. Bioorg. Med. Chem. 2010, 18,
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4. Fujiwara, H.; Matsunaga, K.; Saito, M.; Hagiya, S.; Furukawa, K.-I.; Nakamura,
H.; Ohizumi, Y. Eur. Journal. Pharmacol. 2001, 413, 37.
5. Lee, R. H.; Slate, D. L.; Moretti, R.; Alvi, K. A.; Crews, P. Biochem. Biophys. Res.
Commun. 1992, 184, 765.
6. Nakamura, M.; Kakuda, T.; Qi, J.; Hirata, M.; Shintani, T.; Yoshioka, Y.; Okamoto,
T.; Oba, Y.; Nakamura, H.; Ojika, M. Biosci. Biotechnol. Biochem. 2005, 69, 1749.
7. Laurent, D.; Jullian, V.; Parenty, A.; Knibiehler, M.; Dorin, D.; Schmitt, S.; Lozach,
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0.031 lM). This leads to the conclusion that inhibition of FTase en-
zymes by this compound class does not require an electrophilic
center at C-1, and that further modulation of activity may be pos-
sible by variation of lipophilicity. While the furan-ring containing
natural product halenaquinone was inactive as a growth inhibitor
of P. falciparum,3n orhalquinone (4) and analogues 8, 9 and 11 were
found to be active. In particular the geranyl amine analogue 11 dis-
played the most potent antiplasmodial activity (IC50 0.62 and
0.53 lM). As previously found, the antiplasmodial activity did
not depend on the chloroquine sensitivity of the strain tested
and there did appear to be some correlation between FTase and
P. falciparum activities.
Although good selectivity was observed previously for orhalqui-
none (VERO cytotoxicity IC50 >62 lM), analogues 8–12 all exhib-
ited enhanced cytotoxicity towards the VERO non-malignant cell
line. Of the new compounds studied, geranyl analogue 11 exhibited
the best selectivity towards malaria or FTases.
In conclusion, we have identified the sites of thiol reactivity of
halenaquinone to be the vacant quinonoid positions C-14 and
C-15, while primary amines react preferentially at the keto-furan
C-1 position. The preparation and biological evaluation of a library
of amine analogues of halenaquinone highlighted the importance
of a quinonoid ring and oxygen functionality at C-3 for bioactivity
8. Sakamoto, H.; Furukawa, K.-I.; Matsunaga, K.; Nakamura, H.; Ohizumi, Y.
Biochemistry 1995, 34, 12570.
9. Wipf, P.; Halter, R. J. Org. Biomol. Chem. 2005, 3, 2053.

1264
J. Wang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1261–1264
10. Halenaquinone (1) was isolated from Xestospongia sp. as previously
described.3n +38 (c. 0.212, CH2Cl2) (lit.1 +62.1 (c 0.066, CH2Cl2)); 1H NMR
125.0 (C-18), 102.2 (C-2), 51.9 (C-21), 39.7 (C-6), 37.1 (C-22), 33.0 (C-4), 32.7
(C-5), 28.3 (C-20); (+)-ESIMS m/z 454 [M+H]+; (+)-HRESIMS [M+H]+ 454.1651
(calcd for C28H24NO5, 454.1649).
[a]
D
(DMSO-d6, 300 MHz) d 8.90 (1H, s, H-1), 8.72 (1H, s, H-11), 8.35 (1H, s, H-18),
7.20 (2H, s, H-14 and H-15), 3.12 (1H, ddd, J = 5.0, 13.0, 18.5 Hz, H-4a), 2.94
(1H, ddd, J = 1.5, 5.0, 13.0 Hz, H-5a), 2.69 (1H, J = 1.5, 4.6, 18.5 Hz, H-4b), 2.22
(1H, ddd, J = 4.6, 13.0, 13.0 Hz, H-5b), 1.67 (3H, s, H-20); 13C NMR (DMSO-d6,
75 MHz) d 191.4 (C-3), 184.1 (C-16), 183.7 (C-13), 169.8 (C-9), 154.4 (C-19),
150.9 (C-1), 148.4 (C-7), 143.9 (C-8), 139.0 (C-14 and C-15), 136.3 (C-10), 133.5
(C-17), 130.2 (C-12), 125.0 (C-11), 123.7 (C-18), 122.3 (C-2), 36.6 (C-6), 36.2
(C-4), 32.2 (C-5), 29.7 (C-20).
16. Meissner, A.; Sørensen, O. W. Magn. Reson. Chem. 2001, 39, 49.
17. Norman, B. H.; Paschal, J.; Vlahos, C. J. Bioorg. Med. Chem. Lett. 1995, 5, 1183.
18. n-Pentylamino analogue 9: [
a] +1351 (c. 0.02, CH2Cl2); Rf (SiO2, 1% MeOH/
D
CH2Cl2) 0.32; IR mmax (smear) 1673, 1276 cmÀ1
;
1H NMR (CDCl3, 400 MHz) d
11.72 (1H, br m, NH), 8.91 (1H, s, H-11), 8.59 (1H, d, J = 13.6 Hz, H-1), 8.31 (1H,
s, H-18), 7.04 (2H, s, H-14 and H-15), 3.41 (2H, q, J = 6.8 Hz, H-21), 2.80 (1H, m,
H-4a), 2.62 (1H, m, H-4b), 2.56 (1H, m, H-5a), 1.86 (1H, m, H-5b), 1.69 (2H, m,
H-22), 1.56 (3H, s, H-20), 1.38 (4H, obsc, H-23 and H-24), 0.92 (3H, t, J = 7.0 Hz,
H-25); 13C NMR (CDCl3, 100 MHz) d 195.0 (C-3), 184.5 (C-16), 183.8 (C-13),
176.0 (C-9), 160.7 (C-1), 154.8 (C-19), 139.4 (C-14/C-15), 138.9 (C-15/C-14),
138.1 (C-8), 136.6 (C-7), 133.2 (C-17), 133.2 (C-10), 130.4 (C-12), 125.6 (C-11),
124.9 (C-18), 102.0 (C-2), 50.4 (C-21), 39.7 (C-6), 33.0 (C-4), 32.7 (C-5), 30.2
(C-22), 28.6 (C-23), 28.7 (C-20), 22.2 (C-24), 13.9 (C-25); (+)-ESIMS m/z 420
[M+H]+; (+)-HRESIMS [M+H]+ 420.1810 (calcd for C25H26NO5, 420.1805).
11. 14-(N-Acetyl-L
-cysteinyl)-halenaquinone (5): 1H NMR (DMSO-d6, 400 MHz) d
8.78 (1H, s, H-1), 8.69 (1H, s, H-11), 8.48 (1H, d, J = 8.2 Hz, NH), 8.31 (1H, s,
H-18), 6.93 (1H, s, H-15), 4.57 (1H, m, H-22), 3.38 (1H, m, H-21a), 3.24 (1H, m,
H-21b), 3.08 (1H, ddd, J = 5.0, 13.3, 18.5 Hz, H-4a), 2.92 (1H, m, H-5a), 2.70 (1H,
m, H-4b), 2.21 (1H, ddd, J = 4.7, 13.2, 17.9 Hz, H-5b), 1.88 (3H, s, H-25), 1.65
(3H, s, H-20); (+)-ESIMS m/z 494 [M+H]+; (+)-HRESIMS [M+H]+ 494.0901, calcd
for C25H20NO8S 494.0904.
12. 14,15-Di(N-acetyl-
L
-cysteinyl)-halenaquinone (6): 1H NMR (DMSO-d6,
19. tert-Butoxycarbonylethylenediamine analogue 10: [
a] +794 (c 0.06, CH2Cl2);
D
400 MHz) d 8.90 (1H, s, H-1), 8.70 (1H, s, H-11), 8.32 (1H, s, H-18), 8.29 (2H,
m, NH), 4.49 (2H, m, H-22 and H-27), 3.67 (2H, m, H-21a and H-26a), 3.43 (2H,
m, H-21b and H-26b), 3.08 (1H, m, H-4a), 2.93 (1H, m, H-5a), 2.65 (1H, m,
H-4b), 2.18 (1H, m, H-5b), 1.74 (6H, s, H-25 and H-30), 1.66 (3H, s, H-20); 13C
NMR (DMSO-d6, 100 MHz) d 194.1 (C-3), 177.6 (C-16), 171.6 (C-23 and C-28),
170.0 (C-9), 169.4 (C-24 and C-29), 154.3 (C-19), 151.0 (C-1, 1JCH 215 Hz), 148.5
(C-7), 148.0 (C-14 and C-15), 144.0 (C-8), 136.0 (C-10), 134.8 (C-17), 131.3
(C-12), 125.6 (C-11), 124.4 (C-18), 122.5 (C-2), 52.7 (C-22 and C-27), 38.8 (C-6),
36.6 (C-4), 36.3 (C-21 and C-26), 35.1 (C-5), 29.7 (C-20), 22.2 (C-25 and C-30);
(+)-ESIMS m/z 655 [M+H]+; (+)-HRESIMS [M+H]+ 655.1056 (calcd for
Rf (SiO2, 1% MeOH/CH2Cl2) 0.31; IR mmax (smear) 1702, 1671, 1281 cmÀ1 1H
;
NMR (CDCl3, 400 MHz) d 11.62 (1H, br s, NH), 8.91 (1H, s, H-11), 8.53 (1H, d,
J = 13.2 Hz, H-1), 8.30 (1H, s, H-18), 7.05 (2H, s, H-14 and H-15), 4.86 (1H, br s,
NH), 3.53 (2H, m, H-21), 3.36 (2H, m, H-22), 2.79 (1H, m, H-4a), 2.57 (2H, m,
H-4b and H-5a), 1.85 (1H, m, H-5b), 1.56 (3H, s, H-20), 1.44 (9H, s, H-25); 13C
NMR (CDCl3, 100 MHz) d 195.1 (C-3), 184.8 (C-16), 183.6 (C-13), 176.5 (C-9),
161.0 (C-1), 154.5 (C-19), 139.4 (C-14/C-15), 138.9 (C-15/C-14), 136.0 (C-7),
132.9 (C-17), 131.5 (C-12 and C-10), 125.8 (C-11), 125.0 (C-18), 102.6 (C-2),
79.9 (C-24), 50.1 (C-21), 41.3 (C-22), 39.5 (C-6), 33.0 (C-4), 32.8 (C-5), 28.3
(C-25), 28.2 (C-20), C-23 not observed; (+)-ESIMS m/z 493 [M+H]+; (+)-
HRESIMS [M+H]+ 493.1983 (calcd for C27H29N2O7, 493.1969).
C
30H27N2O11S2, 655.1051).
13. (N
a-Acetyl-
L
-lysinyl)-halenaquinone analogue 7: 1H NMR (DMSO-d6,
20. Geranylamino analogue 11: [
a] +975 (c. 0.12, CH2Cl2); Rf (SiO2, 1% MeOH/
D
300 MHz)
d
11.48 (1H, br m, NH), 8.64 (1H, s, H-11), 8.47 (1H, br d,
CH2Cl2) 0.51; IR mmax (smear) 1671, 1277 cmÀ1 1H NMR (CDCl3, 400 MHz) d
;
J = 12.9 Hz, H-1), 8.33 (1H, s, H-18), 8.03 (1H, d, J = 7.9 Hz, N H), 7.13 (2H, s,
11.65 (1H, br m, NH), 8.91 (1H, s, H-11), 8.62 (1H, d, J = 13.5 Hz, H-1), 8.30 (1H,
s, H-18), 7.04 (2H, s, H-14 and H-15), 5.30 (1H, m, H-22), 5.07 (1H, m, H-27),
4.02 (2H, t, J = 6.1 Hz, H-21), 2.80 (1H, ddd, J = 6.9, 13.0, 19.3 Hz, H-4a), 2.58
(2H, m, H-4b and H-5a), 2.08 (4H, obsc, H-25 and H-26), 1.85 (1H, ddd, J = 6.9,
13.0, 13.0 Hz, H-5b), 1.72 (3H, d, J = 1.0 Hz, H-24), 1.66 (3H, d, J = 1.0 Hz, H-30),
1.60 (3H, s, H-29), 1.56 (3H, s, H-20); 13C NMR (CDCl3, 100 MHz) d 194.9 (C-3),
184.6 (C-16), 183.8 (C-13), 176.0 (C-9), 160.2 (C-1), 154.9 (C-19), 142.5 (C-23),
139.4 (C-14/C-15), 138.9 (C-15/C-14), 138.1 (C-8), 136.8 (C-7), 133.3 (C-17),
132.7 (C-10), 132.1 (C-28), 130.4 (C-12), 125.7 (C-11), 125.0 (C-18), 123.6
(C-27), 118.1 (C-22), 102.3 (C-2), 47.3 (C-21), 39.8 (C-25 or C-26), 39.5 (C-6),
33.0 (C-4), 32.7 (C-5), 28.4 (C-20), 26.3 (C-26 or C-25), 25.6 (C-30), 17.7 (C-29),
16.5 (C-24); (+)-ESIMS m/z 486 [M+H]+; (+)-HRESIMS [M+H]+ 486.2286 (calcd
for C30H32NO5, 486.2275).
a
H-14 and H-15), 4.21 (1H, m, H-25), 3.40 (2H, obsc, H-21), 2.75 (1H, m, H-5a),
2.55 (2H, m, H-5b and H-4a), 1.85 (3H, s, H-28), 1.74 (1H, m, H-4b), 1.67 (2H,
m, H-24), 1.62 (2H, m, H-22), 1.51 (3H, s, H-20), 1.40 (2H, m, H-23); 13C NMR
(DMSO-d6, 75 MHz) d 194.0 (C-3), 184.4 (C-16), 184.0 (C-13), 175.6 (C-9), 173.8
(C-26), 169.4 (C-27), 159.9 (C-1), 154.4 (C-19), 138.6 (C-14 and C-15), 138.3
(C-8), 137.2 (C-7), 133.0 (C-17), 132.9 (C-10), 130.1 (C-12), 124.4 (C-18), 123.4
(C-11), 101.4 (C-2), 51.3 (C-25), 48.8 (C-21), 39.4 (C-6), 32.5 (C-4), 32.4 (C-5),
30.7 (C-24), 29.7 (C-22), 27.4 (C-20); 23.2 (C-28), 22.0 (C-23); (+)-ESIMS m/z
521 [M+H]+; (+)-HRESIMS [M+H]+ 521.1921 (calcd for C28H29N2O8, 521.1918).
14. Representative experimental. An aliquot of phenethylamine (495
lL,
0.020 mmol of a 4.81 mg mLÀ1 solution in CH2Cl2) was added to a solution of
halenaquinone (7.25 mg, 0.022 mmol) in CH2Cl2 (5 mL). The solution was
stirred for 1 hr at room temperature and then dried in vacuo. The crude residue
was purified by silica gel column chromatography (0.5% MeOH/CH2Cl2) to
obtain 8 (9.8 mg) as a dark red oil in 99.0% yield.
21. Glycylmethylester analogue 12: [
a
]
D
+889 (c. 0.09, CH2Cl2); Rf (SiO2, 100%
CH2Cl2) 0.14; IR mmax (smear) 1746, 1671, 1199 cmÀ1
;
1H NMR (CDCl3,
400 MHz) d 11.72 (1H, br m, NH), 8.91 (1H, s, H-11), 8.50 (1H, d, J = 13.0 Hz,
H-1), 8.32 (1H, s, H-18), 7.05 (2H, s, H-14 and H-15), 4.19 (2H, dd, J = 3.7,
5.8 Hz, H-21), 3.82 (3H, s, H-23), 2.82 (1H, ddd, J = 7.2, 12.7, 19.6 Hz, H-4a),
2.63 (2H, m, H-4b and H-5a), 1.88 (1H, ddd, J = 6.7, 13.0, 13.0 Hz, H-5b), 1.57
(3H, s, H-20); 13C NMR (CDCl3, 100 MHz) d 196.0 (C-3), 184.5 (C-16), 183.8
(C-13), 176.5 (C-9), 168.6 (C-22), 160.6 (C-1), 154.9 (C-19), 139.4 (C-14 or
C-15), 139.0 (C-15 or C-14), 138.5 (C-8), 135.5 (C-7), 133.4 (C-17), 132.4 (C-10),
130.4 (C-12), 125.8 (C-11), 125.1 (C-18), 102.4 (C-2), 52.8 (C-23), 50.6 (C-21),
39.7 (C-6), 33.1 (C-4), 32.7 (C-5), 28.2 (C-20); (+)-ESIMS m/z 422 [M+H]+; (+)-
HRESIMS [M+H]+ 422.1240 (calcd for C23H20NO7, 422.1234).
15. Phenylethylamino analogue 8: [
a] +883 (c. 0.08, CH2Cl2); Rf (SiO2, 1% MeOH/
D
CH2Cl2) 0.27; IR mmax (smear) 1672, 1278 cmÀ1
;
1H NMR (CDCl3, 600 MHz) d
11.68 (1H, br m, NH), 8.90 (1H, s, H-11), 8.42 (1H, d, J = 13.2 Hz, H-1), 8.29 (1H,
s, H-18), 7.32 (2H, t, J = 7.6 Hz, H-25 and H-27), 7.24 (1H, m, H-26), 7.20 (2H, d,
J = 7.6 Hz, H-24 and H-28), 7.04 and 7.03 (2H, ABq, J = 10.3 Hz, H-14 and H-15),
3.69 (1H, m, H-21a), 3.62 (1H, m, H-21b), 2.97 (2H, m, H-22), 2.78 (1H, ddd,
J = 7.0, 13.0, 19.0 Hz, H-4a), 2.60 (1H, dd, J = 6.6, 19.0 Hz, H-4b), 2.54 (1H, dd,
J = 7.0, 13.0 Hz, H-5a), 1.84 (1H, ddd, J = 6.6, 13.0, 13.0 Hz, H-5b), 1.53 (3H, s,
H-20); 13C NMR (CDCl3, 150 MHz) d 195.1 (C-3), 184.6 (C-16), 183.8 (C-13),
176.1 (C-9), 160.5 (C-1), 154.8 (C-19), 139.4 (C-15⁄), 138.9 (C-14⁄), 138.2 (C-8),
137.4 (C-23), 136.4 (C-7), 133.3 (C-17), 132.6 (C-10), 130.4 (C-12), 128.9 (C-24/
C-25/C-27/C-28), 128.8 (C-24/C-25/C-27/C-28), 127.0 (C-26), 125.7 (C-11),
22. Evans, M. J.; Cravatt, B. F. Chem. Rev. 2006, 106, 3279.
23. Speers, A. E.; Cravatt, B. F. Chem. Biol. 2004, 11, 535.
24. La Clair, J. J. Nat. Prod. Rep. 2010, 27, 969.