Constitution of proceragenin A - A triterpenoid sapogenin from Albizzia procera benth

Tetrahedron Letters~0.46,pp. 5743-5750, 1966. PeqramonPressLtd. Printedin GreatBritain.

COl?STITUTION OF PROCERAGENIN A - A TRITERPRNOID SAPOGERI19FROM ALBIZZIA PROCERA BRNTH* Sujata Department

Roy and Aelt

Boy

of Chemistry, Botanical of India, Calcutta.

Survey

(Received 8 September1966) The isolation [&X26D

of proceragenin

13” (CHC13); ‘v’ in cm-’

A (Ia)

(KBr)

~C30H4604 (OH);

: 3550

membered laotone); 1360, 1380 (m-dlmethyl). 76.59;

Ii, 9.78;

found:

triterpenoid

aapogenln,

was reported

in a preliminary

with

its

structure

The ethanollc

from the seeds

extract

of the defatted

ethanolic

hydrochloric

and subsequent afforded

Anal. talc. ; H, 9.741,

a

nrocera

This

for

Benth

paper deals

elucidation.

a good amount of saponin,

sapogenin

1765 (a flve-

of Albiaeia

communicationl.

furnished

The acid

C, 76.34

m.p.294-296°r

acid

fraction

proceragenin

of A.

which on hydrolysis

gave acid

and neutral

on treatment

chromatographla

seeds

resolution

mooera

with

sapogenine.

with ethereal

diaeomethane

over acid-washed

A ae one of the constituents.

alumina

Roceragenin

l A part of the work was carried out at the Department of Chemistry, Bose Institute, Calcutta-g, India and was supported in part by the Ministry of Education, Government of India. The authors desire to express their sincere thanks to Dr. A.K.Barua, Reader In Chemistry, Bose Institute, Calcutta and to Rev. Dr. H. Santapau, Director, Botanical Survey of India, Calcutta for their keen interest and encouragement.

5743

A

No.46

5741

naa alao obtained from neutral sapogenin fraction on column chromatographyover acid-washedalumina. ProcerageninA, on hydrolysis with alcoholiccaustic potash, yielded an acid, which on treatmentwith diasomethaneor on standing with alcoholic hydrochloricacid gave back procerageninA.

This is perhaps

the reason why procerageninA is encounteredfrom both the acid and neutral sapogeninfractions during isolation. ProcerageninA (Ia), when treated with pyridine and acetic anhydride at O", furnished a mixture of diacetate (Ic) ~C34H5006, m.p. 246-248O,,@JE6- 38O (CSC13);‘3 in cm-l (KBr) : 1750 (a five-memberedlactone) ;

1725, 1240 (acetate carbonyl)] and

monoacetate (Ib) rCJ2Hq805, m.p. 301-304“,fi@'-

10' (CHC13);

'; in cm-' (KBr): 3600 (OH) ; 1765 (a five-memberedlactone) ; 1720, 1240 (acetatecarbonyl)J.

Acetylationof Ia or of Ib on

steam-bathfurnished only Ic. Ib on oxidationwith chromium trioxide-aceticacid at room temperatureafforded a neutral keto monoacetate. rc32~4605, m.p. 296-302O (decomp.);‘; in cm-1 (KBr): 1765 (a five-memberedlactone);1720, 1240 (acetatecarbonyl)_.7 Thus all the four oxygen atoms in procerageninA are accounted for as forming part of two hydroxyl groups and one la&one ring. The ethylenic linkage in Ia, indicatedby tetranitromethane colour, is very hindered. Ic did neither react with perbensoic 3,4,5,6,7. acid' nor did it react with selenium dioxide Lithium aluminiumhydride reduction of Ia furnished a tetrol (1Ia) f-C30H5004, m.p.306-310°,pJz5+

18.11° (pyridine);

No.46

3 in

5745

cm-' (KBr): 3400 (OH)J

which on acetylation by pyridiae and

acetic anhydride on steam-bath gave a triacetate (IIb) zC36H,3607, m.p. 197-1990, &f-+$8 + 43.2* (CHC13); 5 in cm-l (KBr): 3500 (OH); 1720, 1240 (acetate carbonyl)].

This clearly indicated that one

of the newly formed hydroxyl groups in the tetrol Is highly hindered and cannot be acetylated under the above condition.

The

tetrol triacetate (IIb) consumed one mole of perbenzoic acid at a rate*typical

of the triterpenes of the f-amyrin group having

a double bond at 12:13 position.

The unusually hindered nature

of the ethylenlc linkage in proceragenin A must be then due to the shielding effect of the lactone ring5.

The tetrol triacetate

on oxidation with chromium trioxlde-acetic acid at room temperature furnished a monoketotriacetate (11~) rC36H,3407, m.p. 226-228“. 13.88O (CHC13); 'v in cm-' (KBr) : 1720, 1240 (acetate

@]z3+

carbonyl)J

which on reduction with lithium aluminlum hydride

furnished the tetrol (IIa). bond of the dor

Evidence for the typical 12:13 double

p-amyrin nuc,leuswas obtained by oxidation of

either IIb or IIc with chromium trioxide - acetic acid on steambath to yield an m.p. 26%267O, ( 4.p

A,,

d,p

-unsaturated ketone (IId) zC36H5208,

243 m~~(logc

-unsaturated ketone)J.

4.1); 7 in cm-l (KBr): 1665

The U.V. absorption maximum Is

slightly at a lower wave length than is usually obeerved for 11-keto

Al2 -triterpenes of the

P-amyrin series*.

Lithium

aluminium hydride reduction and subsequent acid treatment of the Gl

-unsaturated ketone (IId) furnished a diene showing triple

ultraviolet absorption maxima at 243, 251, 261 IUJA characteristic

o*

A11:12,

13:18

the basis

-dienee

belonging

bond at the 12:13

the absence

of

acid

diketone

hydroxyl

of this groups

A-diketone

diketone

(Ie)

group thus

was not an 6-

clearly

A

a double

308-312°

or

at C2.

/3 -diketone

eXtinctiOll

amount of dioephenol

of an

in the above

chloride teat’

ketone)J.

both the

system

teat.

for

3-keto

hydroxyl

A and eliminating

group

the poaaibllity

ae the oxidation free

ring

The abeeoce

ferric

the second

-1 5 in cm

product

hydroxyl

group

to Cl or C2.

which gave violet

and ehowed absorption

a colourleas

that

of one secondary

Moreover,

p-diketone,

which showed

(deoomp.);

in nature.

Zimmermann oolour

in prooerageain

acid

of Ia with chromium

demonstrated

&or

gave poeitive

Id and Ie on heating

formation

having

furniahed

was shown by negative

not be attached

mOlecUhr

On

proceragenin

1710 (six-membered

In Ia are secondary

any subatitutlon

product

la&one);

ahowing the presence

at C3 position

could

cC30H4204 , m.p.

diketone

product

group,

Oxidation

at room temperature

or an enolieable

oxidation

of

(Ie)

system.

1770 (five-membered

Formation

g-amyrln

that

A did not consume any periodic

any o(-glycol

trloxide-acetic

of compounde.

is concluded

it

to the

type

poeition.

Proceragenin

(KBr):

g-amyrln

of above observations,

ie a triterpene

neutral

from

with alkali colour

furnished

with alcoholic

maximum at 281 UIJA (loge value

auggeated

that

was formed during

of the above diosphenol

only

a pale ferrio 3.5).

chloride But low

a very amall

eaponification.

can only

yellow

be explained

The if

the

The

*.. a!?@ w

coon

A

Ho

..*

I4

W

“OH

i

OH

NO.16

5748

relative ring

poeition

of one of the hydroxyl

in Ia be a8 shown in (i) .

should the

have the moiety

d-ketol

in alkaline

diosphenol

the tetrol

the moiety

(IIa)

which has previously (IIa)

furnished

a yellow

at 281 my

be deeignated

chloride

triterpene bond.

cannot

(secondary) y.-lactone

eumareeinolic Cl5 (cf.

groups

highly

group

hindered.

The aoid

which gave a violet

colour

maximum

hydroxyl acid’.‘)

eiareeinolic

and it

(excluding series

has already (i).

A

to be

the laotone

ring)

with a 12:15

double

been located The moiety

dlketoproceragenin

was neither

groups

’

show proceragenin

in the moiety

A because

to Zimmermann test

clearly

of the oleaoaoe

and the other

be in ring

of the free

group may

ae Z-hydroxyl

and showed abaorption

pentacyclic

One of the hydroxyl

C5 position

hydroxyl

must have

t 4 .O) .

The above observations a dihydroxy

acid

with chromium trioxlde-acetic

amorphous product

ferric

(log

by the fact

Thus the tetrol

be

the

(iv). strengthened

reagent.

been shown to

on oxidation

with alcoholic

in low yield,

The newly formed secondary

(v).

to aerial

did consume one mole of periodic to this

A

would furnish

susceptible

is further

the sake of convenience

tetrol

being

which should have thti moiety

whereae Ia was inert

for

Thus the diketoproceragenin

medium, may furnish,

The above conclusion that

and the lactone

which on saponification

The latter

(iii).

oxidation

(ii)

groups

A (Ie)

at (i)

responded

an CLor fl diketone.

of Ia can be located

None

at Cg (cf.

(eee paper on dumortierigenin5) and C 15 acidl’ and tomentoeio acid12) as the

No.46

3719

hydroxyl

groups

(whether

hindered

and cannot

on steam-bath.

d or p ) at these

be acetylated

Iecessarily

not be acetylated

steam-bath,

must be aituated

the potential

be in 1:5

diaxial

spontaneous

for

the former

(I)

the oleanane

carboxyl

for rather

has been reported

from nature

or any oxygen function

oleanolic requires

acid

formation

group attached

group is axial

the potential

nature

hydroxyl

of the tetrol axial

hindered

15-keto

(IIa)

reduction group.

C3-OH of proceragenin The low molecular

rotation

to those

uptil

in which there

is a

to C8. .of the

15 lactone

is further

aluminium-hydride)

alcohole

The

by the (11~)

by the

of the highly

(at O”) of the

a normal equatorial (+ 9.9’)

formation

( P).

substantiated

The ease of acetylation

of 3 P-oriented

of

now no

to Cl7 in triterpenes

difference

the

ground aa

in a triterpene

from monoketo triacetate

A suggests

for

two atruotures,

group at Cl5 to be axial

(Lithium

must

evidences

on biogenetic

/3 and the 28 _

of the Cl5 hydroxyl

expected

comparable

attached

A (Ia)

structural

In fact,

than at C8.

on

C6, Cl5 and Clq.

Of these

function

(IIa)

anhydride

With these

A as I and III.

a carboxyl

anhydride

group to account

(IV).

to be more probable

site

The carboxyl

axial

group of proceraganin

to deduce the permissible

appears

series

and acetic

with the ‘Z’-OH

proceragenin

Cl7 is the usual

and acetic

in any of the positions

of the acid

is possible

expressions

triterpene

position

are highly

group in the tetrol

by pyridine

carboxyl

lactonisation

at hand it

by pyridine

the Z-hydroxyl

which could

Further

positions

( p)

orientation.

of Ia an? Ib is and their

acetates.

5750

No.46

The fact that the Cl6 hydroxyl group in procerageninA reeisted acetylatiooat O" euggests its axial (4) configuration. Further the high negative Al value (- 159.32')of Cl6 hydroxgl group of procerageninA also calls for ita sxial configuration(cf. methyl echinocystateand genin A). The above discussionsshow procerageninA to be 28 -

15 la&one

of 15p, 16C-dihydroxy oleanolicacid (IV). IV is a new triterpene acid and is one of the constituentsof the acid sapogeninfraotion of A.

mocerf.

Though procerageninA is a facile lactonisationproduct

of IV, it is difficultto prove that it is not at all occurringin nature.

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C.R.Woller,J.A.C.S.,_, 66

66 (1962).

1269 (1944).

9. D.H.R.Bartonand P.D.Mayo,J.C.S., 887 (1954). 10. L.Ruzicka,O.Jeger, A.Grob and H.Hosll, Helv.Chim.Acta, 3, 2283 (1943). 11.

L.Ruzicka,A.Grob, R.Egli and O.Jeger, Helv.Chlm.Acta, 26, 1218 (1943).

12. L.R.C.Row and G.S.R.S.Rao,TetrahedronLetters, 10.27, 12 (1960).

),