Tetrahedron Letters No. 10, pp 923 - 926, 1978. Pergamon Press. Printed in Great Britain,. STUDIES ON THE BIOSYNTHESIS OF PENTALENOLACTONE.
Letters No. 10, pp 923 - 926, 1978.
Tetrahedron
STUDIES APPLICATION
ON THE BIOSYNTHESIS
OF LONG RANGE SELECTIVE
STRUCTURAL
ELUCIDATION
Pergamon
Printed
OF PENTALENOLACTONE.
PROTON DECOUPLING
OF PENTALENOLACTONE
Press.
in Great Britain,
PART I.
(LSPD) AND SELECTIVE
'%('Hj
NOE IN THE
G
Haruo Seto*, Toru Sasaki,
Hiroshi
Yonehara
and Jun LJzawa+
Institute of Applied Microbiology, The University of Tokyo, Bunkyo-ku, Tokyo, Japan 113 + The Institute of Physical and Chemical Research, Wako-shi, Saitama, Japan 351 (Received
in Japan
We have previously decoupler
keeping
especially
carbons
1977;
studies,
carbons. Two applications one of us (J.U.) observed
in 13C-nmr spectra were enhanced
the said carbons. established
received
An exhaustive
a new promising
During produced
proton
technique
decoupling
a phenomenon
upon selective
16 Jat lu~ 1)
(LSPD)
for the assignments
of this technique
1978) with a
of 13C-nmr spectra,
have been recently
reported
that the signal intensities
irradiation
study on this phenomenon
of protons
using pertinent
in '3C-nmr spectroscopy,
wish to report herein the first application of a natural
in UK for publication
at a weak power level is very useful
ofquaternary
During these
26 Becember
shown that long range selective
viz. selective
of these two techniques
close to
compounds
'3C-('H> NOE
in the structural
.
of some
spatially
model
2)
has 3)
. We
elucidation
product. the course of studies on the biosynthesis of pentalenolactone,G, an antibiotic 4) sp. , we have isolated a pentalenolactone related metabolite named
by Streptomyces
pentalenolactone
G,&
(G means
the sesquiterpenoidal
origin
gem-dimethyl),
the structural
feature of which
implies
strongly
of -IIa (Fig. 1).
C4R
humulene
Ia Ib
: pentalenolactone
After treatment of Streptomyces
G (R=H)
: R=CH3 with diazomethane
of the CHCl3 extract
sp. , followed by purification
te = 3:1, Rf value 0.38.
cf. pentalenolactone
by preparative methyl
IIa
: pentalenolactone
IIb
: R=CH3
of the acidified
(R=H)
fermentation
tic (silica gel, benzene/ethyl
ester , IIb 0.61) was isolated
broth aceta-
pentalenolac-
tone G as its methyl ester, a, ClsHla06 (M+ m/e found 306.1129, calcd. 306.1103), m.p. 125.5', wCDC13 1770cm-1(lactone), lT&O(ketone), 1720(ester) and 1385(gem-dimethyl), no absorption between max 36GO-3CGGcm-1. A::" 238nm(~ 6900) . The proton noise-decoupled,
off-resonance
and selective 923
proton
decoupled
13C-nmr
spectra as
No. 10
924
as
well
of -Ib 5) and comparison
the 'H-nmr spectrum
following
partial
structures
and those in brackets
m
(values show 6,, those
represent
in parentheses
are coupling
revealed
constants
(46.8,48.3) l.l2(s),l.l5(s) [25.3,26.7)
2x -CH3 C-1:44.5,
C-2:147.9,
C-3:122.3,
C-4:59.2
C-5:54.8,
C-5:51.0,
C-6:133.4,
C-7:146.1,
C-8:56.7
C-7:141.6,
C-9:59.1,
C-10:47.1,
C-11:169.4,
The very large the presence
constant
of an epoxide,
above partial
structures,
since the absence
C-12:67.7
C-15:14.6,
coupling
in Hz,
bFig.2
2X-$-
C-13:164- .3, C-14:15.5,
the
6,);
y?.)
0.5) . . -1.05 .-
of these data with those of z,
C-13 ' :52.0
(IJC H =180Hz)
characteristic
of free hydroxy
groups
carbon
C-12:67.6
for three membered
rings
6) revealed
epoxide in IIb being 178Hz 1).
the lJC_H of the corresponding
the oxymethylene
(215.0)
C-8:59.2
C-11:168.7,
C-13 ' :51.8
:c=o
C-6:135.1
(6C 67.6) must be connected
and of other oxygenated
In the
to an ester group,
carbons but for the epoxy
carbons were shown by the IR and 13C-nmr spectra. These partial ('HI NOE3)
structures
experiments
were further
and by taking
coupling
In the gated decoupled
(i) H
10
9
as
H &
a
sharp triplet
Therefore,
(ii)
H 3C
2
H,C
3
H
sharp triplet
of doublets
carbon to a sharp triplet
4
methylene
hydrogens
since no quaternary
three bonds
carbons
In addition
to the above changes,
other methyl
carbon,
The chemical
shifts of these two carbons
the relationship
i.e. the two methyl
of gem-dimethyl,
This sequence was further
irradiation
to c-28!
Irradiation
of C3&
the C-3 methylene
3JC_H=5.9Hz)
Since these two methyls
ones. signal to a
and the C-2 quaternary and C-3
each other in the 'H-nmr spectrum,
except for C-2 were decoupled, from the methyl hydrogens patterns
C-3 and C-2 must be
being
of the methyl
and
irradiated.
signals were simpli-
group are three bonds
away from the
are in a geminal
(6c 25.3 and 26.7) corroborate
relationship. 7) Thus, this conclusion.
C-2 and C-3 have been clarified.
extended
to (ii) by the aid of selective
of CsHz - or gem-dimethyl
to and in similar distances
(C-10) appeared
(2JC_H or 3JC_H) was observed.
groups under consideraion
As shown in Table, the area of the ketone proton
carbon
(1JC_H=125.7Hz,
of one methyl
13C-
into consideration.
('Jc ,=3.7Hz).
the splitting
This means that the protons
and selective
must be non-protonated
(Fig. 3D) collapsed
were not coupled
and two bonds away, respectively,
fied (Fig. 3D).
(Fig. 3B), this methylene
of this methylene
signals
1)
in the 'H-nmr spectrum
and no long range coupling
8
G
as shown below by LSPD
patterns
spectrum
CI and S carbons
LSPD of two methyl '
extended
(C-l) was increased (C-14 and C-15).
to both the CsHz and gem-dimethyl increased
13C-{'H) NOE experiments.
by approximately Therefore, groups,
the area of a quaternary
50 % on selective
the ketone must be close
namely
at the next position
carbon resonance
(&c 48.3) in
925
8
I
I
I
Fig. 3
Pertinent
decoupled,
of the 13C-nmr spectra of 2.
(C) LSPD at 6, 2.15
was dissolved 450,
region
repetition
time 2.7sec,
The conditions
15000 accumulations,
20
(A) proton noise-decoupled,
(CsHz.), and (D) LSPD at 1.10
in CDCls and degassed.
I
I
30
40
50
60
I
I
I
(gem-dimethyl).
(B) gated
The sample
for (C) and (D) were as follows,
data points
16~ ,
decoupler
(80mg)
flip angle
power 8 mG.
The drastic changes in the signal intensities (shown by +) were caused by selective popu9). A double quantum transition mechanism may be the reason of the very complica-
lation transfer ted splitting
addition
pattern
in Fig. 3C (shown by c$)l?)
to that of C-2, but not those of two ester carbonyl
C-4 oould not be a carbonyl.
LSPD
of the same methylene
carbons
eliminated
at C-3 and c-8
were
('JC_h) from c-8
(Fig. 3C).
'H-nmr spectrum,
these two carbons must be in a 1,3_relationship.
about c-8,
which has already
Since the protons
appeared
in the main fragment
(C-11 and C-13). Therefore, the long range coupling
not coupled
each other in the
This structural
of the partial
information
structures
(Fig. 2),
No. 10
Table
connected most of carbon atoms in -* Ib The direc combination of C-l and c-8 was proved by the aid
'3C-{'H) NOE values of -Ib irradiated at 6 1.12
2.22
4.22
4H92
6.82
of chemical manipulation. Reduction of -lb with NaBHs followed by purification by tic (benzene/
CH3
C3Hz
ClzH
C1z.H
C7H
1.53
1.48
1.08
1.15
1.13
1.18
1.71
1.46
1.00
1.00
308, M+- Hz0 found 290.1141, calcd. 290.1154:l)
0.91
1.03
1.66
1.22
1.50
wzF3
0.97
1.13
0.94
1.13
0.90
spectrum, a new proton appeared at 3.75, which
1.03
1.00
1.30
1.27
1.13
was coupled to CsH (J=7.3Hz) and a hydroxy proto
ethyl acetate = 3:l) gave a dihydro derivative which resisted crystallization (C1sHzOOsrM+ m/e 368Ocm-1, 1765 and 1710). In its 'H-nmr
at 1.18 (exchangeablewith DzO).
flip angle 15', repetition time 2.6sec,
Since the remaining bonds of the quaternary
20000 accumulations. The ares obtained by integration were normalized to the solvent
epoxy carbon (C-9) must be connected to non-protonated carbons (aide supra), b
peak (CDCls).
in Fig. 1 is
the only possible structure for pentalenolactone G methyl ester. The structural similarity between -Ib and IIb is in favour of -Ib to be represent ed as shown in Fig. 1 including absolute stereochemistry. Biosynthetically,I&may as illustrated in Fig. 1.
be formed from -Ia via a dihydro derivative through the mechanism Evidences in our hand suggest that Ia may be formed from this hypothe
tical intermediate as a shunt pathway product. References and Footnotes 1) S. Takeuchi, J. Uzawa, H. Seto and H. Yonehara; Tetrahedron Lett. 1977, 2943. 2) K. Isono and J. Uzawa; FEBS Lett. 3,
53 (1977). K. Sakata, J. Uzawa and A. Sakurai; Org.
Mag. Res. in press. 3) J. Uzawa and S. Takeuchi; Org. Mag. Res. received. 4) S. Takeuchi, Y. Ogawa and H. Yonehara; Tetrahedron Lett. 1969, 2737. D. G. Martin, G. Slomp, S. Mizsak, D. J. Duchamp and C. G. Chidester; Tetrahedron Lett. 1970, 4901. 5) 13C-nmr spectra were taken on a JEOL FX-100 spectrometer operating at 25.05 MHz in CDC13 solution and chemical shifts are expressed in ppm from internal TMS. 6) J. B. Stothers; "Carbon-13 NMR Spectroscopy" p.3321 Academic Press, New York. 1972. 7) G. Magnusson, S. Thorn, J. Dahmen and K. Leander; Acta Chim. Scand. B2&
841 (1974).
8) In principle, this sequence of C-l (ketone) and C-2 (quartery carbon) could be clarified by LSPD. However, since C-l was coupled to too many protons [CsH, C7H, CsHz, C14H3 and CrsHsl, the change in signal shape of C-l upon irradiation of only one proton resonance was not discernible at the poor S/N attained. Simultaneous double irradiation (for example CsH2 and gem-dimethyl protons) might be useful for overcoming such problems. 9) A. A. Chalmers, K. G. R. Pachler and L. Wessels; Org. Mag, Res. 6, 445 (1974). H. J. Jakobsen and H. Bildsoe; J. Msg. Res. &,
183 (1977).
10) R. Freeman and W. A. Anderson; J. Chem. Phys. x,
2053 (1962).
11) The technical problems in operating the mass spectrometerused (Hitachi RH-2) prevented to obtain the weak molecular ion peak in the high resolution mass spectrum.