Absolute configuration of amphidinol 3, the first complete structure determination from amphidinol homologues: Application of a new configuration analysis based on carbon-hydrogen spin-coupling constants [8]

Full text of DOI:10.1021/ja983655x

870
J. Am. Chem. Soc. 1999, 121, 870-871
Absolute Configuration of Amphidinol 3, the First
Complete Structure Determination from Amphidinol
Homologues: Application of a New Configuration
Analysis Based on Carbon-Hydrogen Spin-Coupling
Constants
Michio Murata,* Shigeru Matsuoka, Nobuaki Matsumori,
Gopal K. Paul, and Kazuo Tachibana
Department of Chemistry, School of Science
The UniVersity of Tokyo, Hongo, Bunkyo-ku
Tokyo 113-0033, Japan
Figure 1. Rotamers and coupling constants for C32-C33 (a) and C38-
C39 (b). *J values for each rotamer estimated from stereochemically
known compounds.3a (c) 2
JC,H values depend on the dihedral angle
ReceiVed October 19, 1998
ReVised Manuscript ReceiVed December 9, 1998
between an oxygen atom on a relevant carbon and a proton on a
neighboring carbon; in 1,2-dioxygenated systems such as C32-C33 (a),
2
the anti O/H orientation gives JC,H of 0 to +2 Hz while the gauche
Dinoflagellates, a type of primitive unicellular algae, are a rich
source of structurally and biologically intriguing natural products;
e.g., okadaic acid, brevetoxins, ciguatoxins, and maitotoxin.
Among these polyether-cyclic compounds, amphidinols are unique
dinoflagellate metabolites since they are primarily made up of
linear polyhydroxy structures. The first member of this group was
isolated from the dinoflagellate Amphidinium klebsii as a potent
orientation gives 2JC,H of -4 to -6 Hz.8
3JH,H and 2,3
C
,
H
5
J
v
a
l
u
e
s
o
f
i
n
t
a
c
t
1
w
e
r
e
m
e
a
s
u
r
e
d
b
y
E
.
C
O
S
Y
1
a
antifungal substance by Yasumoto’s group. A series of
homologues1 has since been found in the same genus, and
Kobayashi’s group reported closely related compounds, luteopha-
b,c
2
nols. These long-chain polyhydroxy compounds may be one of
the most challenging targets for stereostructural elucidation since
chiral centers are scattered over a flexible acyclic structure. Thus,
little is known of the nature of the stereogenic centers in
amphidinols.
3
We recently developed J-based configuration analysis, which
6
and hetero half-filtered TOCSY (HETLOC), respectively; phase-
sensitive HMBC7 was also used for parts where the small
has been proven to be a powerful tool for the stereochemical
determination of acyclic structures.3b In this method, 1,2-diaster-
magnetization transfer by TOCSY hampered the accurate mea-
C,H by HETLOC. C32-C33 and C38-C39 can
be used as examples to see how the J-based analysis works in
eomeric relationships between chiral centers are determined by
choosing a correct staggered rotamer among six possibilities
arising from erythro and threo configurations using spin-coupling
surement of 2
,3
J
3
3
2,3
2
3a
configuration assignments. As shown in Figure 1a, J(H-32, H-33)
constants ( JH,H and
JC,H, e.g., see Figure 1c for JC,H). In this
revealed a value that is typical of gauche interaction for a 1,2-
paper, we report the complete configuration of amphidinol 3 (1),
a representative homologue of the amphidinol family, mainly
using this J-based method.
diol system.3 The values for J(C32, H-33) and J(C34, H-32)
a
2
3
8
indicate that H-33 is anti to C32-OH and H-32 is gauche to C34,
respectively. These interactions unambiguously establish the threo
configuration for C32-C33, as depicted in Figure 1a. For C38-
C39, J(H-38, H-39), which is intermediate between anti and
gauche, suggests that this bond undergoes a conformational
change. The J-based analysis can even be applied to such a
From cellular extracts of A. klebsii obtained from 440 L of
culture, 12 mg of 1 was isolated together with other amphidinol
3
1
b,c
2,3
homologues. To facilitate measurements of
J
C,H, we prepared
1
3
13
a
C-enriched sample of 1 (25% C, 8 mg) by making another
culture (200 L) in the presence of 12 mM NaH CO .
3
1
3
3
flexible system. The two small values for J(C37, H-39) and
J(C40, H-38) indicate gauche C37/H-39 and gauche C40/H-38
The stereochemical assignment of 1 was accomplished as
3
3
follows; (a) the J-based method was used for acyclic parts with
interactions in both conformers (Figure 1b). Of the six possible
pairs of alternating rotamers arising from erythro and threo
configurations, only one pair in Figure 1b satisfies all of these
requirements. The relative configurations of the consecutive
stereogenic center in C20-C27 can be determined using this
method, as shown in Figure 2. The diastereomeric relationships
of C44-C45 and C50-C51 were assigned in the same manner
1
,2- and 1,3-chiral centers, C20-C27, C32-C34, C38-C39,
C44-C45, and C50-C51; (b) NOE analysis combined with J
analysis was used for two ether cycles and their linkage C39-
4
C44; (c) the modified Mosher method and chromatographic/NMR
comparison were used for degradation products to determine the
absolute stereochemistry at C2, C6, C10, C14, C23, and C39.
3
2,3
(1) (a) Satake, M.; Murata, M.; Yasumoto, T.; Fujita, T.; Naoki, H. J. Am.
on the basis of JH,H and
JC,H. The configurations of rings A/B
Chem. Soc. 1991, 113, 9859-9861. (b) Paul, G. K.; Matsumori, N.; Murata,
M.; Tachibana, K. Tetrahedron Lett. 1995, 36, 6279-6282. The planar
structure of 1: (c) Paul, G. K.; Matsumori, N.; Konoki, K.; Sasaki, M.; Murata,
M.; Tachibana, K. In Harmful and Toxic Algal Blooms; Yasumoto, T., Oshima,
Y., Fukuyo, Y., Eds.; UNESCO: Paris, 1996; pp 503-506.
9
and their linkage (C39-C44) were elucidated using NOEs in
3
2,3
combination with JH,H and
JC,H data (see Supporting Informa-
tion).
(
2) Doi, Y.; Ishibashi, M.; Nakamichi, H.; Kosaka, T.; Ishikawa, T.;
Kobayashi, J. J. Org. Chem. 1997, 62, 3820-3823.
3) (a) Matsumori, N.; Kaneno, D.; Murata, M.; Nakamura, H.; Tachibana,
K. J. Org. Chem. in press. Applications of this method have been published.
b) Matsumori, N.; Nonomura, T.; Sasaki, M.; Murata, M.; Tachibana, K.;
Satake, M.; Yasumoto, T. Tetrahedron Lett. 1996, 37, 1269-1272.
4) Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J. Am. Chem. Soc.
991, 113, 4092-4096.
(5) Griesinger, C.; Sørensen, O. W.; Ernst, R. R. J. Am. Chem. Soc. 1985,
107, 6394-6396.
(
(6) Kurz, M.; Schmieder, P.; Kessler, H. Angew. Chem., Int. Ed. Engl. 1991,
30, 1329-1331.
(
(7) Zhu, G.; Live, D.; Bax, A. J. Am. Chem. Soc. 1994, 116, 8370-8371.
2
(8) Dependence of JC,H on the dihedral orientation of oxygen functions
(
has been investigated (e.g., Schwarcz, J. A.; Cyr, N.; Perlin, A. S. Can. J.
Chem. 1975, 53, 1872-1875).
1
1
0.1021/ja983655x CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/16/1999

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 4, 1999 871
graphed on a chiral resolution column15 and determined to be an
(S)-enantiomer. Considering all of these partial configurations led
to the complete structure of amphidinol 3 with the absolute
stereochemistry of 2S, 6R, 10R, 14R, 20S, 21S, 23S, 24R, 25S,
2
4
7S, 32R, 33S, 34R, 35R, 36R, 38R, 39R, 43R, 44R, 45R, 47R,
8R, 49R, 50S, and 51R.
Despite recent progress in the NMR-based configuration
analysis of natural products, chemical degradation in combination
with partial synthesis is still considered the sole reliable method
for determining the stereochemistry in acyclic structures, which
often requires a fairly large amount of sample, as in the pioneering
Figure 2. Configuration and conformation for C20-C27 of 1 established
16
studies of mycoticins by Schreiber’s group, nystatin by Beau’s
2
,3
3
on the basis of
J
C,H and JH,H. Broken lines with arrows and numbers
17
18
group, and roflamycoin by Rychnovsky’s group. In this study,
we were able to perform a complete structural determination using
only 3 mg of the sample for all of the chemical degradations and
2
,3
3
indicate
J
C,H in Hz, and plain lines denote JH,H in Hz. For pairs of
9
vicinal carbons, except C24-C25, two anti orientations of H/H, C/H,
and/or O/H can be assigned on the basis of
2
,3
3
JC,H/ JH,H, which results in
8
mg of the 13C-enriched sample for NMR measurements. This
elucidation of the 1,2-diastereomeric relationship (for methine-methylene
pairs such as C21-C22, the stereospecific assignment of methylene
considerable reduction in sample size is mainly attributable to
the J-based configuration analysis, since 12 of 17 chiral centers
3
a
protons can also be attained).
in the acyclic parts of 1 were established by this method.
Therefore, 2
,3
J
C,H should be reevaluated as a useful parameter for
These NMR-based analyses using intact 1 have revealed the
relative configurations of C20-C27 and C32-C51. Next, their
absolute configurations and those at C2, C6, C10, and C14 were
configuration assignments of acyclic stereogenic centers in natural
products.
investigated using degradation products; treatment of 1 with HIO
4
/
Acknowledgment. This study was supported by Special Coordination
Funds from the Science and Technology Agency Japan (Asian Network
on Microbial Research) and by the “Research for the Future” program
of the Japan Society for the Promotion of Science (JSPS-RFTF96I00301).
We are grateful to Dr. M. Sasaki in our laboratory and Professor T.
Kusumi, Tokushima University, for their discussions and to Dr. M.
Nakamura in our department for his help with the GC analysis.
NaBH , followed by esterification with (R)- and (S)-MTPA (2-
4
methoxy-2-trifluoromethyl-2-phenylacetic acid) and separation by
HPLC, furnished MTPA esters of fragments corresponding to
C2-C20 (2b,c), C21-C24 (3b) and C33-C50 (4b,c).10 The
Supporting Information Available: Selected spectra used for
configuration assignments of 1 and their interpretations; HETLOC and
HMBC for measurement of 2
,3
J
C,H, NOESY and ROESY (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
JA983655X
(11) As shown below, the stereochemistry at C6 and C14 can be determined
to be 6R and 14R based on the distribution of ∆δ (2b - 2c), in which positive
values are observed in C15-C20, while negative ones are seen in C2-C5.
The configuration of C10 could also be assigned since ∆δ of C8 and C12 are
zero. This can only be accounted for by the R configuration at C10, since the
shielding effect at C8 (or C12) from a phenyl group of (S)-MTPA at C10 (or
C14) should be equal to that from an (R)-MTPA at C6 (or C10).
absolute stereochemistries of C6, C10, C14,11 and C3912 were
(
12) The ∆δ values of (4b - 4c) were as follows: CDCl
3
, 500 MHz, H
2
2
-
elucidated by the modified Mosher method using 2b/2c and 4b/
3
7, -0.12/-0.06; H-38, -0.57; H-39, -0.14; H-40, +0.37; H
-41, +0.30/
4
4
c. The configuration of 3a was determined to be 23S by
+0.37; H
2
-70, +0.33/+0.42. These data show that C39 has an R configuration,
since the clear separation of negative and positive values with respect to C39
shows that the ∆δ values were predominately affected by the MTPA group
on C39 rather than by other MTPA groups on relatively remote sites.
(13) (R)-Methyl-1,4-butanediol was prepared from dimethyl-(R)-methyl-
comparison of the NMR data of the bis-(R)-MTPA esters 3b with
S)- and (R)-MTPA esters of authentic (R)-methyl-1,4-butane-
(
13
diol. The configuration of C2 was determined using the C1-
C4 fragment obtained from the O-benzyloxy-methyl derivative
succinate by LiAlH
4
reduction, followed by esterification with (R)- and (S)-
MTPA. H NMR of 3b was identical to that of the (S)-ester of the authentic
diol; 3b and (S)-ester (CDCl , 500 MHz) δ 3.98, 3.92, 3.82, 3.73, 1.53, 1.38,
.05, 0.52. (R)-ester δ 3.97, 3.93, 3.83, 3.70, 1.52, 1.38, 1.05, 0.52.
14) A procedure that was previously reported for ciguatoxin was fol-
1
14
of 1 by treatment with OsO
4
/NaIO
4
.
The resulting 1,2-diben-
3
1
zyloxylmethoxy-butyl p-bromobenzoate (5b) was chromato-
(
lowed: Satake, M.; Morohashi, A.; Oguri, H.; Oishi, T.; Hirama, H.; Harada,
N.; Yasumoto, T. J. Am. Chem. Soc. 1997, 119, 11325-11326.
(15) Chiral resolution was performed on CHIRALPAK AD (φ 4.6 × 250
mm, DAICEL) eluted with hexane-1-propanol (25: 1). Authentic (S)-ester
and the derivative from 1 (5b) were eluted at 16 min 50 sec and 16 min 59
sec, respectively, while (R)-ester appeared at 19 min 13 sec.
(16) Schreiber, S. L.; Goulet, M. T. Tetrahedron Lett. 1987, 28, 6001-
6004.
(17) Lancelin, J.-M.; Beau J.-M. Tetrahedron Lett. 1989, 30, 4521-4524.
(18) Rychnovsky, S. D.; Griesgraber, G.; Schlegel, R. J. Am. Chem. Soc.
1995, 117, 197-210.
(
9) Among 14 vicinal methine-methine interactions in the acyclic parts
3
of 1, there are four H/H-anti orientations, which were indicated by J (H-24,
3
3
H-25) ) 8.0 Hz, J(H-33, H-34) ) 9.5 Hz, J(H-43, H-44) ) 9.0 Hz, and
3
J(H-49, H-50) ) 10.0 Hz. For configuration assignments of these parts,
3
a
additional NOE information is necessary. Diastereomeric relations between
C24 and C25, C33 and C34, C43 and C44, and C49 and C50 were established
by key NOEs between H-23 and C25-OH, H-32 and H-38, C43-OH and
H-45, and H-45 and H-51, respectively. See Supporting Information for details.
(
10) MTPA esters 2b (690 µg), 2c (520 µg), 3b (30 µg), 4b (400 µg), and
4
c (150 µg) were obtained from 3.0 mg of 1. See Supporting Information.