Studies on the biosynthesis of pentalenolactone. Part I. Application of

0 downloads 0 Views 588KB Size Report
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.