Published on Web 02/23/2012
r2012 American Chemical Society
Vol. 14, No. 5
Tripartilactam, a Cyclobutane-Bearing
Tricyclic Lactam from a Streptomyces sp.
in a Dung Beetle’s Brood Ball
Seon-Hui Park,†Kyuho Moon,†Hea-Son Bang,§Seong-Hwan Kim,†Dong-Gyu Kim,†
Jongheon Shin,†and Dong-Chan Oh*,†
Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea, Department of Agricultural
Environment, National Academy of Agricultural Science, Suwon 441-707, Republic of
Korea, and Department of Agricultural Biotechnology, College of Agriculture and Life
Science, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-921, Republic
Received January 16, 2012
Tripartilactam, a structurally unprecedented cyclobutane-bearing tricyclic lactam metabolite, was discovered from Streptomyces sp. isolated
spectroscopy and multistep chemical derivatization. Tripartilactam was evaluated as a Naþ/KþATPase inhibitor (IC50= 16.6 μg/mL).
Diverse insect ecosystems have recently drawn signifi-
cant attention as a new source of natural products with
pharmaceutical potential.1This attention is partly due to
secondary metabolites with selective activity, as shown in
the ecologically well-defined symbiotic systems of the
southern pine beetle (Dendroctonus frontalis)2and the
the potential of microorganisms discovered in insect eco-
communities are unexplored niches. The recent study of
the mud dauber, Sceliphron caementarium, led to the
discovery of a novel antifungal polyene macrocyclic lac-
tam, sceiliphrolactam, although its ecological role has not
been completely determined.4Biomedical investigation of
the gut microbiota of a mantis isolated a fungal species,
Daldinia eschscholzii, that produces new immunosuppres-
sive polyketides known as dalesconols.5Even a fungal
strain isolated from the nest of the fungus-growing
ant (A. dentigerum) yielded a new polyketide
The dung beetle, Copris tripartitus, is a soil-dwelling
insect, the life cycle of which is tightly dependent on the
feces of herbivores.7The brood balls mainly composed of
feces are expected to harbor extensive microbial commu-
nities. Our recentselectiveisolation ofactinomycetes from
†Natural Products Research Institute, College of Pharmacy, Seoul Na-
§National Academy of Agricultural Science.
Department of Agricultural Biotechnology, College of Agriculture and
Life Science, Seoul National University.
Bode, H. B. Angew. Chem., Int. Ed. 2009, 48, 6394. (c) Kaltenpoth, M.
Trends Microbiol. 2009, 17, 529.
(2) (a) Scott, J. J.; Oh, D.-C.; Yuceer, M. C.; Klepzig, K. D.; Clardy,
J.; Currie, C. R. Science2008, 322, 63. (b) Oh, D.-C.; Scott, J. J.; Currie,
C. R.; Clardy, J. Org. Lett. 2009, 11, 633.
2009, 5, 391.
(4) (a) Oh, D.-C.; Poulsen, M.; Currie, C. R.; Clardy, J. Org. Lett.
One 2011, 6, e16763.
(5) Zhang, Y. L.; Ge, H. M.; Zhao, W.; Dong, H.; Xu, Q.; Li, S. H.;
(6) Freinkman, E.; Oh, D.-C.; Scott, J. J.; Currie, C. R.; Clardy, J.
Tetrahedron Lett. 2009, 50, 6834.
Org. Lett., Vol. 14, No. 5, 20121259
the beetle’s brood balls revealed the diversity of the
actinomycetous population and their potential as a new
We have continuously investigated the chemical and
biological diversity of the actinomycetes isolated from
dung brood balls in the search for structurally novel
bioactive compounds. In our chemical analysis of the
actinomycetes’ secondary metabolites, we discovered a
with a distinct UV spectrum (λmaxat 277 nm). Further
characterization of this compound’s structure led us to
identify an unprecedented cyclobutane-bearing tricyclic
lactam, tripartilactam (1). Herein, we report the isolation,
structural determination, stereochemistry, and biological
activity of this novel tricyclic lactam.
The molecular formula, C28H35NO6, was deduced based
on1H and13C NMR spectral data (Table 1) and FAB
high-resolution mass spectrometry (observed [MþH]þat
m/z: 482.2542, calculated: 482.2543). The13C NMR spec-
trum displayed a polyunsaturated signature with 12 car-
bon signals from δC 147.0 to 121.7. Three carbonyl
on the carbon chemical shift and the IR absorption at
carbons were identified at δC78.7, 74.2, and 70.2. The
upfield region ofthe13C NMR spectrumdisplayed signals
for 10 aliphatic carbons (Table 1).
The1H NMR spectrum contained signals for a poly-
unsaturated feature consistent with 10 olefinic protons
from 7.10 to 5.23 ppm and two allylic methyl groups
(δH1.49 and 1.26), accounting for six double bonds indi-
The amide functionality was also confirmed by the ob-
servation of the NH signal at δH7.99. In addition, tripar-
tilactam showed three carbinol protons (δH4.52, 4.02,
3.82) along with three D2O exchangeable proton signals
also supported by the broad IR absorption at 3361 cm?1.
In the aliphatic region, one doublet representing a methyl
the IR spectrum revealed that this compound bears six
double bonds and three carbonyl groups, which account
for 9 out of 12 unsaturation equivalents calculated from
the molecular formula. Thus, tripartilactam (1) must be a
established the isolated spin system from C-19 to 25-NH,
including the connectivity between C-28 (aliphatic methyl
group; δC19.0?δH0.93) and C-24 (methine; δC38.2?δH
2.32) (Figure 1). The COSY correlations among the ali-
phatic methines (C-8 δC38.0?δH2.57; C-9 δC48.6?δH
2.38; C-16 δC 44.4?δH 3.54; C-17 δC 52.2?δH 2.43)
surprisingly revealed the existence of a cyclobutane ring.
Further extension of this spin system includes C-7, C-15,
and C-14 according to the COSY and the HMBC correla-
tions. The triol moiety (C-11 to C-13), a discrete double
bond (C-4 and C-5), and an isolated methylene (C-2) were
Table 1. NMR Data for Tripartilactam (1) in DMSO-d6
mult (J in Hz)
ddd (12.0, 10.0, 10.0)
br d (2.5)
br d (4.0)
dd (7.5, 3.5)
br d (7.5)
ddd (10.0, 5.0, 2.5)
ddd (10.0, 4.0, 2.5)
dd (14.5, 11.0)
dd (14.5, 10.0)
dd (15.0, 10.0)
dd (15.0, 9.0)
ddd (13.0, 4.0, 4.0)
dd (8.0, 4.0)
a500 MHz.b125 MHz.cOverlapped.
(7) Fincher, G. T. J. Ga. Entomol. Soc. 1981, 16, 316.
(9) The bacterialstrain SNA112was isolated froma dung broodball
The 16S rDNA analysis resulted in placing SNA112 in the genus
Streptomyces because it is most closely related to Streptomyces corchorusii
(10) Tripartilactam (1): yellowpowder; [R]D=?128(c 0.20, MeOH);
IR (neat) νmax3361, 2922, 1723, 1677, 1581 cm?1; UV (MeOH) λmax
(log ε) 277 (4.51) nm; NMR spectral data, see Table 1; HR-FAB MS
[MþH]þm/z 482.2542 (C28H35NO6) calcd [MþH]þ482.2543.
1260 Org. Lett., Vol. 14, No. 5, 2012
also identified, based on the
COSY spectrum (Figure 1).
spectrum verified the connectivities of these spin systems.
The coupling from H2-2 to the carbonyl carbons C-1 and
C-3 located the methylene C-2 between these carbonyl
and from H3-26 to C-5, C-6, and C-7 established the
connectivity from C-1 to the cyclobutane ring. The triol
partial structure was found to be connected to the cyclo-
This assigned location is also further supported by the
long-range correlations from H-16 and H-17 to C-10. The
allylic methyl signal (H3-27) generated strong HMBC
correlations toC-17, C-18, andC-19,connectingthe chain
presence of an 18-membered macrocyclic ring was con-
Although no correlations in the COSY, HMBC, and
ROESY spectra in three different solvents (DMSO-d6,
pyridine-d5, and CD3OD) were observed to directly con-
nect C-13 to C-14, this linkage was deduced based on the
molecular formula; this linkage completed the planar
structure of 1 bearing a cyclooctene ring.
the analysis of1H?1H coupling constants and ROESY
correlations (Figure 1). The large coupling constant be-
tween H-4 and H-5 (15.5 Hz) established the 4E config-
correlations between H3-26 and H-4. The
coupling (10.0 Hz) between H-14 and H-15 determined
14Z. The H-20-H-21 trans coupling constant (14.5 Hz)
established 20E. The 22E configuration was assigned
based on the large coupling between H-22 and H-23
(15.0 Hz). Finally, the 18E configuration was deduced by
the ROESY correlation between H3-27 and H-20.
Because the coupling constants between the protons in
cyclobutane are not sufficiently specific to determine the
relative configuration in the ring,11the relative configura-
tion of the cyclobutane ring was established by careful
1H?1H couplings in the
The ROESY correlations in the cyclobutane and cyclo-
octene rings indicated that the relative configurations of
11R*, 12R*, 13R*, 16R*, and 17S*, respectively.
determined by multistep chemical degradation (Figure 3).
Tripartilactam was subjected to ozonolysis and acid hy-
drolysis to yield 3-amino-2-methyl-propioinic acid (2).
This β-amino acid (2) was derivatized with the Sanger
reagent to generate a product (3) with improved UV
absorption and retention in reversed-phase HPLC. Com-
methyl ester (PGME) to furnish (S)- and (R)-PGME
amide products (4a and 4b, respectively). Analysis of the
1H NMR spectra allowed the assignment of the proton
chemical shifts in 4a and 4b. Calculation of the ΔδS-R
values clearly established the absolute configuration of
C-24 as R based on the consistent distribution of the signs
Figure 1. Key ROESY, COSY, and HMBC correlations estab-
lishing the planar structure of tripartilactam (1).
Figure 2. Key ROESY correlations of the cyclobutane and
cyclooctene ring in tripartilactam (1).
Figure3. Multistepchemical degradation andderivatization for
the determination of the absolute configuration of the C-24
(11) Pretsch, E.; B€ uhlmann, P.; Affolter, C. Structure Determination
of Organic Compounds-Tables of Spectral Data; Springer: New York,
2000; p 176.
(12) Yabuuchi, T.; Kusumi, T. J. Org. Chem. 2000, 65, 397.
Org. Lett., Vol. 14, No. 5, 20121261
cyclobutane and cyclooctene were determined by the
application of the modified Mosher method using (R)-
and (S)-R-methoxy-(trifluoromethyl) phenyl acetyl chlo-
ride(MTPA-Cl).Sincetripartilactam bearsthree consecu-
tive hydroxy groups at C-11, C-12, and C-13, it was
challenging to generate mono-MTPA esters. After a sig-
nificant amount of effort on reaction optimization, we
tried a short reaction time (5 min) and succeeded in ob-
taining mono-(S)- and (R)-MTPA ester selectively at the
alcohol of C-13 (5a and 5b). Analysis of1H NMR and
COSY spectral data for these MTPA esters allowed the
assignment of the ΔδS-Rvalues, which sufficiently estab-
Based on the relative configuration, the absolute config-
urations of the chiral centers C-8, C-9, C-11, C-12, C-16,
and C-17 were determined as 8R, 9R, 11R, 12R, 16R,
The biological activity of 1 was evaluated first in cell-
based antimicrobial and anticancer assays, in which no
significant inhibition against various pathogenic bacterial
and fungal strains was observed (see Supporting Informa-
tion (SI)). This compound was also inactive against
the A549 lung cancer cell line and the HCT116 colon
observed to be a moderate inhibitor of Naþ/KþATPase,
with an IC50value of 16.6 μg/mL.
The structure of 1 is unique because of the existence of
cyclobutane linking the 8- and 18-membered rings. This
ring structure could be formed by a photochemically
derived [2 þ 2] cycloaddition reaction14of the two double
bonds at positions 8 and 16 in a putative macrocyclic
lactam precursor (see SI Figure S3).
soft corals.16However, the 4-, 8-, and 18-membered tri-
cyclic structure of 1 is an unprecedented carbon skeleton,
to the best of our knowledge.
The discovery of tripartilactam with a novel carbon
scaffold provides additional evidence that microbial com-
munities of insect habitats could be promising sources of
structurally novel bioactive natural products.
Kim in SNU, Yousung Jung in KAIST, and Michael
Fischbach in UCSF for valuable discussions about cyclobu-
Research Foundation of Korea (NRF) grants funded by the
Korean government (MEST) (No. 2011-0015931) and (No.
International Early Career Scientist.
bioassay data, a proposed biosynthetic pathway of 1, and
NMR spectra of 1, 3, 4a, 4b, 5a, and 5b. This material is
Figure 4. ΔδS-Rvalues in ppm for the S- and R-PGME amide
products (4a and 4b) in CD3OD.
and 5b) in DMSO-d6.
(13) Seco, J. M.; Qui~ no? a, E.; Riguera, R. Tetrahedron: Asymmetry
2001, 12, 2915.
(14) We propose that this [2 þ 2] cycloaddition is photochemically
derived because we could not find any precedent example of enzymatic
could not completely exclude the possibility of the enzymatic involve-
photochemical [2 þ 2] cycloaddition, see: Carruthers, W. Cycloaddition
possible cyclobutane formation mechanism by unusual oxidative cycli-
zation or radical cascading proposed in the ladderane biosynthesis, see:
Rattary, J. E.; Strous, M.; Op den Camp, H. J. M.; Schouten, S.; Jetten,
M. S. M.; Damst? e, J. S. S. Biol. Direct 2009, 4, 8.
(15) (a) Jacobsson, U.; Kumar, V.; Saminathan, S. Phytochemistry
1995, 39, 839. (b) Macleod, J. K.; Rasmussen, H. B. Phytochemistry
1999, 50, 105.
(16) (a) Sung, P.-J.; Chuang, L.-F.; Kuo, J.; Chen, J.-J.; Fan, T.-Y.;
Kashman, Y. Tetrahedron 1983, 39, 3385.
The authors declare no competing financial interest.