Jasisoquinolines A and B, architecturally new isoquinolines, from a marine sponge Jaspis sp.

Article abstract of DOI:10.1021/ol201823w

Two architecturally new isoquinolines, jasisoquinolines A and B, were isolated from a marine sponge Jaspis sp. as cathepsin B inhibitors. Their structures were determined by a combination of spectroscopic analyses and chemical methods. Both jasisoquinolin

Full text of DOI:10.1021/ol201823w

ORGANIC
LETTERS
2011
Vol. 13, No. 18
4798–4801
Jasisoquinolines A and B, Architecturally
New Isoquinolines, from a Marine Sponge
Jaspis sp.
Yasufumi Imae,† Kentaro Takada,† Shuhei Murayama,† Shigeru Okada,† Yuji Ise,‡ and
Shigeki Matsunaga*,†
Laboratory of Aquatic Natural Products Chemistry, Graduate School of Agricultural
and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan,
and Misaki Marine Biological Station, The University of Tokyo, Miura,
Kanagawa 238-0225, Japan
assmats@mail.ecc.u-tokyo.ac.jp
Received July 7, 2011
ABSTRACT
Two architecturally new isoquinolines, jasisoquinolines A and B, were isolated from a marine sponge Jaspis sp. as cathepsin B inhibitors. Their
structures were determined by a combination of spectroscopic analyses and chemical methods. Both jasisoquinolines A and B inhibit cathepsin B
with an IC50 value of 10 μg/mL.
Cathepsin B occupies a central node of the proteolytic
signal amplification network in mammals.1 Enhanced
levels of genes and proteins of this papain family of
lysosomal cysteine protease in tumor cells,2,3 together
with the diminution of invasive nature of metastatic
tumor cells in the gene knockout and knockdown
experiments of this enzyme,4,5 justify cathepsin B to
be a target for anticancer therapy.6 In the course of our
screening of the extracts of marine invertebrates for
cathepsin B inhibitors, we found activity in a marine
sponge Jaspis sp. Bioassay-guided fractionation of the
extract led us to isolate new isoquinoline alkaloids,
named jasisoquinolines A (1) and B (2). In this paper,
we describe the isolation and structure elucidation of
jasisoquinolines.
The MeOH and EtOH extracts of the marine sponge
(400 g, wet weight) were combined and subjected to
solvent partitioning, silica gel column chromatogra-
phy, ODS flash chromatography, and RP-HPLC se-
quentially to afford jasisoquinoline A (1, 2.0 mg) and
† Laboratory of Aquatic Natural Products Chemistry.
‡ Misaki Marine Biological Station.
(1) Manson, S. D.; Joyce, J. A. Trends Cell Biol. 2011, 21, 228–237.
(2) Roshy, S.; Sloane, B. F.; Moin, K. Cancer Metast. Rev. 2003, 22,
271–286.
(7) Takada, K.; Uehara, T.; Nakao, Y.; Matsunaga, S.; van Soest,
R. W. M.; Fusetani, N. J. Am. Chem. Soc. 2004, 126, 187–193.
(8) Bowen, E. G.; Wardrop, D. J. J. Am. Chem. Soc. 2009, 131, 6062–
6063.
(3) Yan, S.; Sloane, B. F. Biol. Chem. 2003, 384, 845–854.
(4) Nalla, A. K.; Gorantla, B.; Gondi, C. S.; Lakka, S. S.; Rao, J. S.
Cancer Gene Ther. 2010, 17, 599–613.
(5) Gocheva, V.; Zeng, W.; Ke, D.; Klimstra, D.; Reinheckel, T.;
Peters, C.; Hanahan, D.; Joyce, J. A. Genes Dev. 2006, 20, 543–556.
(6) Gocheva, V.; Joyce, J. A. Cell Cycle 2007, 6, 60–64.
(9) (a) Kushi, Y.; Honda, S.; Ishizuka, I. J. Biochem. (Tokyo) 1985,
97, 419–428. (b) Murata, M.; Naoki, H.; Matsunaga, S.; Satake, M.;
Yasumoto, T. J. Am. Chem. Soc. 1994, 116, 7098–7107.
(10) Singh, S. B. Tetrahedron Lett. 2000, 41, 6973–6976.
(11) Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J. Am.
Chem. Soc. 1991, 113, 4092–4096.
r
10.1021/ol201823w
Published on Web 08/15/2011
2011 American Chemical Society

jasisoquinoline B (2, 0.7 mg), together with the known
schulzeines A (3, 4.0 mg) and C (4, 1.5 mg).7,8
Jasisoquinoline A (1) had a molecular formula of C45H71-
O17N2S3Na3 as determined by HRFABMS. Two fragment
ion peaks due to desulfation (m/z 951 and 849) in the nega-
tive FABMS suggested the presence of three sulfate groups,
because the latter ion was presumed to contain one negatively
charged sulfate group.9 An analysis of the 1H NMR data in
combination with the HSQC spectrum showed the presence
of five aromatic protons, three oxygenated methines, two
nitrogenous methylenes, one doublet methyl, one triplet
methyl, and a large methylene envelope (Table S1). One aro-
matic resonance integrated for 2H (δ 6.10, H-60 and H-100)
was meta-coupled to another aromatic signal (δ 6.12, H-80),
suggesting the presence of a 5-substituted resorcinol. In the
HMBC spectrum these aromatic protons were correlated to
oxygenated aromatic carbons (δ 159.4, C-70 and C-90) and a
carbon at δ 142.1 (C-50); the latter was connected to a 2-sub-
stituted ethyl group. The substituent was shown to be a nitro-
genonthebasisofthe1Hand13C chemical shift data (δC 41.9,
C-30; δH 3.51 and 3.43, H2-30; Figure 1a, substructure A). The
remaining aromatic signals were meta-coupled to each other.
Interpretation of the COSY and HMBC data demonstrated
the presence of a 4,5-disubstituted resorcinol moiety. This
resorcinol moiety was also linked to a 2-substituted ethyl
group, the substituent being assigned as a nitrogen on the
basis of the 1Hand13C chemical shifts of the methylene group
(δC 40.9, δH 3.39 and 3.03, substructure B). Substructure C
encompassed three oxymethines, one branched methyl, and
six methylenes. The planar structure of this moiety, which
was identical with a partial structure of schulzeine A (3),7 was
assigned by analysis of 2D NMR data (Figure 1a). The
coincidence of the 1H and 13C chemical shifts suggested the
identity of the relative configurations of these units.
Figure 1. Partial structures of jasisoquinoline A (1).
There was a pair of methylene protons (H2-9) coupled
only to another pair of methylene protons (H2-10). In the
HMBC spectrum H2-9 was correlated to a nitrogenous
quaternary carbon (C-1), an aromatic carbon (C-8a), and a
carbonyl carbon (C-10). Additional HMBC correlations
from H2-3 to C-1, and NH-20 and H2-30 to C-10 demonstrated
the formation of an isoquinoline ring by incorporating C-1 to
which was attached C-9 and C-10 amide carbonyl carbon
(Figure 1b). ROESY cross peaks between NH-20 and H-3ax,
between 8-OH and H2-9, and between H2-4 and H-5 sup-
ported the structure of the isoquinoline moiety (Figure 1c).
There remained one terminal methyl and 13 methylene
carbons unassigned. Therefore, substructure C should be
placed in the middle of a long alkyl chain emanating from
C-9. The location and orientation of substructure C in the
alkyl chain was determined by taking advantage of the
presence of a vicinal disulfate.7 Sulfate esters in jasisoquino-
line A (1) were removed with p-TsOH,10 and the resulting
triol was oxidized with NaIO4 (Scheme 1a). The product was
reduced with NaBH4 to furnish diol 6 and 3-methyldecanol
(7). The FABMS data of 6 [m/z 601 (M þ H)þ] were
consistent with the oxidation at C-21, C-24, and C-25 in 5.
This assignment was supported by the tandem FABMS data
of 5 (Figure S17ꢀS22). The absolute configuration of C-27
was determined by inspection of the 1H NMR data of 7 after
Org. Lett., Vol. 13, No. 18, 2011
4799

ring and a negative 1Lb band were observed for schulzeine B
(Figure S23). It is well documented that the sign of the 1Lb
band of the fused benzene system is basically determined by
the helicity of the cyclohexene, tetrahydropyridine, or dihy-
dropyran ring (Figure 3), but the sign could be reversed by
factors such as (1) polar substituent(s) of the benzene ring
and (2) an axial substituent at the benzylic position.14 Judging
Scheme 1. Chemical Degradation of Jasisoquinoline A (1)
1
from the signs of Lb bands in schulzeines, it was demon-
strated that substitution of the benzene ring by two OH
groups did not reverse the relationship between the helicity
and the sign of the 1Lb band in isoquinolines: P- orM-helicity
corresponds to a positive or negative 1Lb band, respectively.15
We were able to assign the conformation of the tetrahydro-
pyridine ring of jasisoquinoline A (1) on the basis of the
ROESY data (Figure 1c) and observed a positive 1Lb band.
1
However, the sign of the Lb band is variable due to the
presence of an axial substituent at the benzylic position.
Because of the lack of suitable examples, it is not possible
to assess the effect of quaternalization of the benzylic position
1
toward the sign of the Lb band. Therefore, we tentatively
draw the structure of 1by taking into account the positive 1Lb
band and by presuming that its sign was not reversed by
substituents at C-1 (Figure 3).
converting to the (R)-MTPA ester 8 (Scheme 1b).11 The 1H
NMR spectra of the (S)- and (R)-MTPA esters of 3-methyl-
1-alkanols give charasteristic patterns for the oxygenated
methylene protons by reflecting the configuration of the
methyl branch.7,12 The 1H NMR data of 8 were consistent
with the corresponding ester of the 3R-alkanols, indicating
the 27R configuration. Because the relative configuration of
the C-21 to C-27 portion was suggested to be identical with
that of the corresponding portion of 3, configurations at
C-21, C-24, and C-25 were deduced to be all S.
We initially anticipated determining the absolute config-
uration of the C-1 quaternary carbon by applying the exciton
chirality method13 because of the presence of two chromo-
phoric resorcinol moieties. However, in the CD spectrum of 1
(Figure 2), no exciton split was observed near the absorption
maximum of resorcinol rings (280 nm). Instead a positive 1Lb
transition was observed at 280 nm.14 The conformation of
the tetrahydropyridine ring in schulzeine A had been assigned
on the basis of the ROESY data, and its absolute configura-
tion had been determined by the modified Mosher analysis.7
A positive 1Lb band of schulzeine A (Figure S23) was consis-
tent with the P-helicity of the tetrahydropyridine ring. On
the other hand the M-helicity of the tetrahydropyridine
Figure 2. CD spectrum of jasisoquinoline A (1).
(12) (a) Oikawa, H.; Matsuda, I.; Kagawa, T.; Ichikawa, A.; Kohmoto,
K. Tetrahedron 1994, 50, 13347–13368. (b) Eguchi, T.; Kobayashi, K.;
Uesaka, H.; Ohashi, Y.; Mizoue, K.; Matsushima, Y.; Kakinuma, K. Org.
Lett. 2002, 4, 3383–3386.
(13) Nakanishi, K.; Berova, N. In Circular Dichroism, Principles and
applications; Nakanishi, K., Berova, N., Woody, R. W., Eds; VCH Publish-
ers, Inc.: New York, 1994; Chapter 13.
(14) (a) Snatzke, G.; Ho, P. C. Tetrahedron 1971, 27, 3645–3653. (b)
ꢀ
Snatzke, G.; Kajtar, M.; Werner-Zamojska, F. Tetrahedron 1972, 28, 281–
ꢀ
288. (c) Snatzke, G.; Kajtar, M.; Snatzke, F. In Fundamental Aspects and
Figure 3. Helicity of the tetrahydropyridine ring of jasisoquino-
line A (1). The bold lines represent the benzene rings.
Recent Developments in Optical Rotatory Dispersion and Circular Dichroism;
Ciardelli, F., Salvadori, P., Eds; Heyden: London, 1973; Chapter 3.4. (d) Toda, J.;
Matsumoto, S.; Saitoh, T.; Sano, T. Chem. Pharm. Bull. 2000, 48, 91–98.
4800
Org. Lett., Vol. 13, No. 18, 2011

Jasisoquinoline B (2) was smaller than 1 by a CH2 unit.
The 1H NMR spectrum of 2 was almost identical with that
of 1 except for the absence of the secondary methyl signal.
Interpretation of the COSY, HSQC, and HMBC data of 2
suggested that 2 was the 27-desmethyl analog of 1. This was
confirmed by the ESIMS of the NaIO4 oxidation product of
the desulfated 2.
schulzeines to jasisoquinolines, by R-oxidation of the
fatty acid to be used as a substrate for a PictetꢀSpengler
reaction, is intriguing. It is worth noting that jasisoquino-
lines are, to the best of our knowledge, the first examples
of natural products containing the amide form of 5-(2-
aminoethyl)resorcinol.
Both jasisoquinolines A (1) and B (2) inhibit cathepsin B
with an IC50 value of 10 μg/mL. Schulzeines A (3) and C (4)
also showed inhibitory activity against cathepsin B with IC50
values of 5.0 and 12 μg/mL, respectively. Upon desulfation
the cathepsin B inhibitory activity of 1was no longer detected,
indicating the involvement of sulfate esters in the activity.
Jasisoquinolines are new members of isoquinolines from
marine invertebrates. They are traced to a polyketide path-
way, considering the substitution pattern in the benzene
ring: biosynthesis of isoquinolines via a polyketide pathway
is well-documented.16 Diversification of the structures of
Acknowledgment. We thank the officers and crew of
T/S Toyoshio-maru of Hiroshima University for their
assistance in collecting the sponge specimen. We acknowl-
edge Prof. Dr. K. Hori, Hiroshima University, for the
arrangement of the cruise. We thank Mr. H. Ozawa for
his assistance in measuring CD spectra. We appreciate
ꢀ
Dr. T. Kurtan for valuable discussions on the interpreta-
tion of CD data. This work was partially supported by a
Grant-in-Aid from the Ministry of Education, Culture,
Sports, and Technology of Japan.
Supporting Information Available. Experimental de-
tails; NMR data tables for 1 and 2; 1D and 2D NMR
1
spectra for 1 and 2; H NMR spectra for 3, 4, and 8;
ꢀ
€ ꢀ
ꢀ
(15) Kerti, G.; Kurtan, T.; Illyes, T. -Z.; Kover, K. E.; Solyom, S.;
Pescitelli, G.; Fujioka, N.; Berova, N.; Antus, S. Eur. J. Org. Chem.
2007, 2007, 296–305.
€
(16) (a) Bringmann, G.; Wohlfarth, M.; Rischer, H.; Grune, M.;
tandem FABMS spectrum for 1; and CD spectra for
schulzeines. This material is available free of charge via
in Internet at http://pubs.acs.org.
Schlauer, J. Angew. Chem., Int. Ed. 2000, 39, 1464–1466. (b) Bringmann,
G.; Irmer, A.; Feineis, D.; Gulder, T. A. M.; Fiedler, H.-P. Phytochemistry
2009, 70, 1776–1786.
Org. Lett., Vol. 13, No. 18, 2011
4801