Caulerpenyne, an unusual sequiterpenoid from the green alga caulerpa prolifera

TetrahedronLettersNo. 38, PP 3593 - 35%. OPergamon Reee Ltd. 1978. Printedin Great Britain.

CAULERPENYNE, AN UNUSUAL SEQUITERPENOID FROM THE GREEN ALGA CAULERPA PROLIFERA

Vincenzo Amico, Giovanna Oriente, Mario Piattelli+ and Corrado Trinyali Istituto di Chimica Organica dell'universita di Catania Viale Doria, Catania, Italy and Ernest0 Fattorusso, Silvana Mayno and Luciano Mayo1 Istituto di Chimica Organica dell'universita di

Napoli

Via Mezzocannone 16, Napoli, Italy

Investigation of marine algae of the genus Caulerpa has resulted in and nitrogenous compounds. 3

the isolation of diterpenes,' triterpenes As part we

of

a

study

have investigated

Lamour.

of

the

the

metabolites of Mediterranean seaweeds,l

green

alga

Caulerpa

prolifera

( Forsk.)

We wish to report here that this plant produces the acetylenic

sesquiterpenoid

caulerpenyne,

_. 1 CH2OR

/.

I,

tivcH20R

I

2

R=H

2

R=OAc

Repeated silica gel chromatography of the chloroform extract of the alga

(collected Syracuse, Sicily, Italy, July, 1977)

isolation, in

yield

caulerpenyne,

m.p. 57-58”,

prisms

purified by

of

0.35% [a]

based go

on

fresh

resulted

seaweed

weight,

= +7.1" (c 1 in EtOH) as

recristallization

from

ethanol.

in the

The

of

colourless elemental

composition of compound 1_,which was by far the most abundant component (22%) of the lipid extract,

was determined as

3593

C2,H2606

by

elemental

3594

No. 38

analysis.

In the

mass

spectrum the molecular ion was not discernible

and fragments were observed at cm/e 314 (M+-HOA=), 230 (M+-HOAc-2CH2C0 ) and

212

(M+-2HOAc-CH2CO),

acetoxy groups. 1750

(vinyl

at 2200 cm 280 (sh)

-1

at

169.3,

spectrum

to

the

presence of three

exhibited carbonyl

with

E 33100,

presence

and

84.9

167.3

and

olefinic carbons

27900

of

and

252, 265 (sh)

17000.

The

c.m.r. spectrum

and

three

166.5

for

the

(doublets

at

acetoxy

groups

(singlets

ester carbonyls), two

136.7

and

133.9)

carbon atom (doublet at

six

108.8, d;

methyl quartets

105.1, d 1, a

and the third to a

68.5). This spectrum also

one triple

2.15

is

(31.7, t) and

(3H each, s)

These

data

containing

The p.m.r. spectrum (270 MHz, CDC13)

representative

2.07

and

121.2,

d:

an acyclic sesquiterpenoid

and four double bonds.

exhibited signals

methylene carbon

(24.4; 20.5; 20.5; 20.2; 20.2; 17.3).

suggested that caulerpenyne

at

attached to

comprised six additional olefinic carbons (147.5, s; 129.4, s; 118.4, s;

and

a non-terminal acetylenic group (singlets

ppm)

secondary saturated

absorption at

CmC stretch band

, while the U.V. spectrum showed 1:::

the

93.8

i.r.

pointed

acetate) and 1735 (acetate), and a weak

nm

confirmed

The

which

of

three acetoxymethyls

and, in

the olefinic

at 6 2.18,

region, three

IH

double doublets at 6 7.64 (J=12.5 and 0.8 Hz), 5.83 (J=12.5 and 0.7 Hz) and

7.26

shifts5 J

(J=O.8 for

values

and

protons

are

also

0.7 Hz), at Cl,

consistent

C2

and Cl3

in accordance

system. 5

trans-1,4-diacetoxy-1,3_butadiene at C4 was seen as a triplet at protons 7.5

and

quartet 3H

appeared 7.5 Hz)

as

two

with

and

2.47.

(J=7.5, 7.5 and 1.4 Hz) at

doublet

(J=1.4 Hz) at

molecule were cis-II-Me) quartets which were

expected

chemical

respectively. The

observed

those recorded for a

trans,

The acetoxymethine

proton

6 5.87 (J=7.5 Hz), while the

symmetrical

at 6 2.64

with

double

A one-proton

6 ,I .83 to 7-Me.

3H doublets at

1.81

(J=l.l Hz,

trans-II-Me),

(J-l.1

and

1.1 Hz) at

6 5.35

extensive

decouplings,

and a in

the

d 1.89 (Jr1.1

HZ,

and

(10-H).

(J=l5,

double double

The other protons

and

by

doublets

6 5.69 was assigned to 6-H

accounted for by two

confirmed

double

methylene

a 1H

quartet of

These attributions, allowed

to clarify

the

sequences

proton

(in EtOAc

at

O",

refluxing

Et20

C,-C3,

20 min)

afforded

C,O-C,2.

Ozonolysis

established 1_ for

the

of

with excess (isolated

pentane-1,2,3,5-tetraol

formula

the

and consequently

and

followed by reduction

this

tetraphenylurethane) ;

C4-C7

caulerpenyne

LAH in the

as

attachment of

j_

to c4

C3

was unambiguously

determined. Additional evidence to confirm structure

sodium borohydride reduction to the expected diol

M+

234,

267,

v ii;

3300

283 with

CDC13)

showed

4.08

l-HZ),

12 hr

at

in the

at

2.43

Assignment of by application frequency absorption

g

also 13-H, 25%, which

increased

The

by n.o.e.; the

in

addition

single bond. Also the

l-HZ) and to

Overhauser

(Ac20/Py,

2 (OH absorption absent

and

0.46 C6

4.54

2

the

of

preferred

the

was

not

C3 double bond

6 7.26, the

was

at

the integrated

whereas the 6-H signal

(4-H)

13-H2)

1 was made -

irradiation

effect;

irradiation at

that

(2H, s,

double bond in

configuration of

6 5.87

methylenes

ppm, respectively.

in a 20% enhancement

system

b 5.82

was

frequency

of

(2-H) by ca.

unaffected, conformation

a result of

the

is trans-coplanar with respect to C2-C3

values of the

are summarized in Table 1,

J=6 Hz,

5.55 (IH, t, J=7

acetylation

intensity of the signal at

whereas the triplet at

diacetoxy-1,3-butadiene

ture.

0.39

the methylene signal,

confirmed

shows

J=6 Hz,

resulted

significantly affected.

(2H, t,

(IH, s, IO-H), On

(2H, t, J=7

and 2.06 and the carbinol

configuration

7-Me

of

6 2.03

nuclear

3.76

1.90

318, whose p.m.r. spectrum exhibited two

shifts of

of

of

5.40br

M+

(2H, t,

downfield

2.90br

(2H, t, J=6 Hz, 2-H2),

2 gave the diacetate

'1gH26'4'

4.15

at

(6H,

(IH, t, J=7 Hz, 6-H).

acetoxymethyl signals at

showing

6 1.82

(2H, D20-exchangeable, 2 OH),

room temp.),

appeared

(sh),

7-Me and trans-II-Me),

5.80

i.r.1,

C15H2202'

1 ;$H255

(CeC),

signals

(2H, s, 13-H2),

and

Hz, 4-H)

2170 cm-'

Its p.m.r. spectrum (90 MHz,

3.52

Hz, 5-H2),

and

oily,

21

by

E 18000, 22800 and 18000.

cis-II-Me), _

(3H, s,

(OH)

also obtained

j_ was

europium

induced shifts,

which

were in agreement with the proposed

struc-

No. 38

3596

Table 1. 'H Induced Shifts of Caulerpenyne in the presence of Eu(fod13 12

Proton

Lb” 7.19

4.12

solvent

a=

5

4

10.75

CDC13;

The chirality

2.54

of

to

two

be

a

at

levorotatory,

that 6

This work

13

2.73

0.21

0.80

6.93

tetraphenylurethane

levorotatory mixture

on account

considering

12

14

15

AcO

1.34 -0.61 2.89 3.33 4.30

was established by the following observation.

C4

diastereoisomers,

separated

10

LSR/Substrate = 1

Pentane-1,2,3,5_tetraol shown

6

small

both

2(E)-3(S)-

this result

as

( [a]:' = -21°, 5

evidently

of the

obtained

epimers amounts and

shows that

at

above

1

C2,

was

in dioxane) not

which were

Nonetheless,

available.

2(S)-3(S)-diastereoisomers are at

chirality

C4 in

1 -

is

S.

was carried out in the frame of the "Progetto finalizsato

per 1'Oceanografi.a e i Fondi Marini",

C.N.R.,

ROME.

References 1.

A.G. Blackman and R.J. Wells, Tetrahedron Letters, 1976,

2.

G.A. Santos and M.S. Doty, Llovdia, 1971, 34,

3.

M.S. Doty and G.A. Santos, J. Chem. E.

4.

Nature,

2729.

88.

1976, 211, 990;

G.A. Santos,

C, 1970, 842.

E. rattorusso, S. Magno, L. MayoI, C. Santacroce, D. Sica, V. Amico, G. Oriente, M. Piattelli and C. Tringali, Tetrahedron Letters, 1976, 937;

E. Fattorusso, S. Magno, L. Mayol, C. Santacroce,

D. Sica, V.

J.C.S. Chem. =., Amico, G. Oriente, M. Piattelli and C. Tringali, _-1976,426;

V. Zunico, G. Oriente, M. Piattelli, C. Tringali, E. Fat-

torusso, S. Magno and L. Mayol, ibid., 1069; V. Amico, G. Oriente, M. Piattelli, C. Tringali, E. Fattorusso, S. Magno and L. MayoI, Experientia, 1977, 33, 989. 5.

G.E. McCasIand, S. Furuta and L.J. Durham, 2. w.

m.,

1968,

33,

2835. 6.

E. Hardegger, M. Schellenbaum, R. Huwyler and A. Ztlst, -Helv. e,

1957,

40,

1815.

(Receivedin UK 4 July 19'78; aeoeptedfor plblioation20 July 1978)

Chim.