Guanidine derivatives having hypotensive activity, composition containing them and process for obtaining them

Guanidine derivatives of the following formulas (1) and (2): ##STR1## wherein: R.sup.1 is hydrogen or optionally substituted cinnamoyl, PA0 R.sup.2 is hydrogen, alkyl or alkenyl, with the proviso that R.sup.1 and R.sup.2 cannot be both hydrogen, PA0 n is an integer from 1 to 8, or: ##STR2## wherein R.sup.3 is truxinoyl or a truxilloyl each optionally substituted, and PA0 R.sup.2 and n are as defined above; pharmaceutical compositions containing such compounds and a process for their extraction and purification from plant material, in particular from Verbesina caracasana.

The present invention relates to new guanidine derivatives having 
hypotensive activity, to the compositions containing the same and to a 
process for their production, consisting in extracting and purifying said 
products from plant materials. More particularly, this invention relates 
to novel compounds whose formula comprises the guanidine group, which 
compounds show a remarkable hypotensive activity. 
In the field of therapeutical treatment of hypertension some active 
principles of the class of guanidines are already known, the most 
widespread among them being guanetidine, whose molecule is made up of an 
8-membered heterocyclic saturated ring, containing one nitrogen atom, 
which nitrogen atom is 1inked to a chain having two methylene groups and 
ending in the guanidine group. 
Other guanidine compounds known as antihypertensive agents are guanfacine 
and guanabenz, both characterized by a structure having a benzene ring 
substituted with two chlorine atoms at one end and having the guanidine 
group at the other end. 
However, all such products are obtained by chemical synthesis, and it is 
well known to those who are skilled in the art that this feature gives 
generally higher risks of toxicity with respect to substances of natural 
origin, because of the possible presence in the final product of trace 
amounts of reagents, of intermediate compounds and/or reaction 
by-products. Moreover, it is also well known that drugs obtained by 
synthesis generally require production processes which are more expensive 
and more complex than drugs obtained from natural sources. 
Accordingly, the object of the present invention is to provide guanidine 
compounds that show a hypotensive activity comparable to or higher than 
the activity of compounds already known, but that can be obtained from 
largely available natural sources through simple and economically 
convenient extraction and purification procedures. 
Studies and experimentations carried out to that aim within the present 
invention resulted in the isolation of a series of guanidine compounds 
from the extract of a plant, the Verbesina caracasana (Compositae), which 
compounds showed a remarkable hypotensive activity. Although only the 
above-mentioned species has been investigated, it cannot be excluded that 
similar compounds (which are water soluble) can be found in other species 
of Verbesina, especially if the fact is considered that preceding 
phytochemical studies reported in the literature for such genus are in all 
cases limited to the examination of the liposoluble components. 
Further to the newly isolated guanidine compounds, a number of structurally 
related compounds have been synthesized and tested, thereby resulting in 
the definition of a new class of guanidine derivatives showing remarkable 
hypotensive activity. 
Accordingly, the present invention provides new guanidine derivatives 
having either of the following general formulas: 
##STR3## 
wherein: R.sup.1 is hydrogen or optionally substituted cinnamoyl, i.e.: 
##STR4## 
where R represents hydrogen or one or more substituents, R.sup.2 is 
hydrogen, alkyl or alkenyl, with the proviso that R.sup.1 and R.sup.2 
cannot be both hydrogen, and 
n is an integer from 1 to 8, and 
R.sup.3 is truxinoyl or truxilloyl, each optionally substituted, i.e., 
respectively: 
##STR5## 
where R has the same meaning as above. 
Preferably, the alkyl or alkenyl group R.sup.2 has up to 5 carbon atoms; 
more preferably, R.sup.2 is prenyl, i.e. 3-methyl-2-butenyl. 
More specifically, the invention includes the following four compounds 
which have been isolated and identified in the extract of Verbesina 
caracasana: 
##STR6## 
Compound (3) has been called guanido-I, and is comprised in the general 
formula (1) for R.sup.1= 3,4-dimethoxycinnamoyl, n=4 and R.sup.2= prenyl; 
compound (4), called guanido-III, as a matter of practice is a 
prenylagmatine (agmatine, which is already known, is 
4-(aminobutyl)guanidine); compound (5) has been called guanido-V and it 
can be practically derived from guanido-I without the prenyl radical on 
the guanidine group; compound (6) comes within the general formula (2) 
when R.sup.3 is bis(3,4-dimethoxy).beta.truxinoyl, n is 4, R.sup.2 is 
prenyl, and it has been called diguanido-II. 
It can be easily recognized that compounds (4) and (5) (guanido-III and -V) 
are fragments of the molecule of the guanido-I, and that diguanido-II has 
a structure deriving from a dimerization of guanido-I through addition to 
the double bonds. 
Chemical characterization of the preferred compounds of the present 
invention will be given further on in the example, and the pharmacological 
data proving the high hypotensive activity of said compounds will also be 
reported. 
The invention also includes pharmaceutical compositions for treating 
hypertension containing, as the active ingredient, one of the guanidine 
compounds of the formulas (1) or (2), or a mixture of two or more of said 
compounds, or even an unfractionated extract of Verbesina, in particular 
of Verbesina caracasana. 
The present invention further provides an extraction and purification 
process for obtaining the above-mentioned compounds from plant materials, 
said process being characterized in that it comprises the operations of: 
a) treating the plant material, made into small pieces or ground, with an 
alcoholic solvent for extraction; 
b) removing the solvent in vacuo; 
c) distributing the extraction residue between ethyl acetate and water; 
d) subjecting the water fraction to lyophilization (freezedrying). 
Preferably, in order to increase the purity of the product, the raw 
lyophilized extract from the last above-mentioned operation is suspended 
again in an anhydrous alcoholic solvent and filtered, so as to remove any 
remaining insoluble material, which is made up mainly of inorganic salts; 
then the solvent is removed by evaporation, and a new, purified raw 
extract is obtained. In order to further increase the purity of such 
product, the preceding operation can be repeated a number of times with 
decreasing volumes of the alcoholic solvent. 
To obtain a higher yield of the compounds of the invention it is also 
preferable to recover through water extraction the possible part of the 
active principle left behind in solution in the ethyl acetate employed in 
step c). 
As an alternative to the process disclosed above, it is possible to 
substitute a water extraction at room temperature for the steps a), b) and 
c), with substantially similar yields. 
The raw extract resulting from step d) (or the purified product obtained 
according to the preferred procedure) is then subjected to a process for 
separating the components on a silica column, eluting with chloroform 
containing increasing amounts of methanol; said separation can also be 
performed employing Sephadex LH-20 and eluting with methanol. 
In addition to the extraction process proposed above, which by the moment 
represents a simple and economic way for producing the guanidine compounds 
of the invention, it is also possible to provide other production 
techniques, such as for instance biotechnological processes from plant 
cell cultures, seedlings, immobilized cells or even from microorganisms 
(bacteria, yeasts). 
Furthermore, the compounds of the invention may be prepared by chemical 
synthesis, by adapting methods already known, for instance as described in 
some of the following examples.