CA1240692A

CA1240692A - Synthetic phospholipid compounds and their method of preparation and use

Info

Publication number: CA1240692A
Application number: CA000448924A
Authority: CA
Inventors: Barry D. Sears
Original assignee: Lipid Specialties Inc
Current assignee: Lipid Specialties Inc
Priority date: 1983-03-07
Filing date: 1984-03-06
Publication date: 1988-08-16
Also published as: JPH047353B2; DE3474667D1; ATE38039T1; US4534899A; EP0118316B1; EP0118316A2; JPS59204198A; EP0118316A3

Abstract

ABSTRACT OF THE DISCLOSURE
Synthetic phospholipid compounds are disclosed, which compounds are phosphatidylethanolamine polycarboxyl polyalkylene glycols. The compounds are prepared by the reaction of a phosphatidylethanolamine, a polycarboxylic acid, such as succinic or glutaryl anhydride, and a polyalkylene glycol, such as polyethylene glycol. The compounds are useful in solubilizing, in an aqueous environment, water-insoluble compounds.

Description

1;~'1~692 - This invention relates to novel, improved, phospholipid compounds and to a method cf preparation and to the use of such compour.ds 7 particularly in solubilizing, in an aqueous environment, water-insoluble compounds.
Phospholipids, such as lecithinJ are amphipathic compounds in that they consist of both hydrophobic and hydrophilic groups or regions within the same molecule. The balance between these hydrophobic and hydrophilic regions determines their physical properties in an aqueous environment. The '.- uses of natural phospholipids as additives are numerous in the food industry (for example, as emulsifiers~, in cosmetics, for industrial uses and for the pharmaceutical industry, especially in the preparation of drug-delivery systems.
United States Patents 4,086,257; 4,097,502; 4,145,410; and 4,159,988 disclose various modifications of the polar-head-group region of natural phospholipids which lead to unique and unexpected physical properties.
Further, various derivatives of lecithin are known, such as, for example, oxyalkylated lecithin compounds (see United States Patents 3,085,100 and 2,310,679) and phosphatidylalkanolamine derivative ~see, for example, United States Patents 2,801,255; 3,542,820; 3,577,466; and 4,254,115). It is desirable to provide novel, synthetic phospholipids, particularly having enhanced solubility and surfactant properties in an aqueous environment, es-pecially for the formulation of water-insoluble materials, such as drugs or cosmetic ingredients, within an aqueous environment.
Applicant's copending Canadian patent application serial number 407,514 describes novel, synthetic phospholipid compounds, such as phosphatidyl-alkanolamine carboxyl polyalkylene glycol like phosphatidylethanolamine car-boxyl polyethylene glycol compounds. These novel compounds are prepared by the covalent reaction of a carboxylic analog of the polyalkylene glycol with ~ 7 lZ~ 2 the phosphatidylalkanolamine, to provide novel, biodegradable, phospholipid compounds which contain an amide linkage.
The present invention describes a new, improved series of phos-pholipid compounds in which the polar-head-group region is modified by the covalent attachment through two or more carboxylic groups of polyalkylene gly-cols. The novel, synthetic phospholipid compounds of the invention are phos-phatidylalkanolamine polycarboxyl polyalkylene glycol compounds, such as '-- phosphatidylethanolamine di or tri carboxyl polyethylene and polypropylene glycol compounds. The phospholipids of the invention are analogs of the phospholipid compounds of copending application Serial Number 407~514. This invention also provides a different and improved method of coupling the poly alkylene glycol polymer to the phospholipid. The phospholipid compounds of the invention, like the compounds of the copending application, have enhanced surfactant properties, are soluble in acetone and are biodegradable.
The phospholipids of the invention are represented by the follow-ing structural formula:

H

HC - O-R
f ~-) HC -O-R O or OH R O O

2 i 16 ~
HC - O - P - O - R4 - N - C - R5 - C - O -~R~ - O ~ X

wherein:
a) Rl and R2 each represent hydrogen or a saturated or unsaturated, Z straight or branch-chain acyl groups, and especially an organic acyl radicals having 2 to 24 carbon atoms; for example, C2 to C20 fatty-acid radicals, such as oleic~ stearic, linoleic, linolenic, palmitic, myristic or arachidonic acid, or may be derived from natural products, such as plants like soybean or egg;

--b) R3 represents an alkylene radical, and especially a C2 to C4 group like ethylene, propylene or butylene; that is, tetramethylene;
c) R4 represents a polymethylene radical, typically a C2 to C10 polymethylene divalent radical, and particularly an ethylene radical, that is, a dimethylene radical, as in natural lecithin, or a propylene radical; that is, a trimethylene radical;
d) R5 represents an organic linking radical; for example, a ' hydrocarbon radical, of from about 1 to 24 carbon atoms, but typically from about 2, 3 or 4 carbon atoms, which radical may be saturated or unsaturated, may be substituted, for example, with hydroxyl, amino or carboxyl groups, or be an unsubstituted radical, such as a polymethylene (-CH2-) radical like an ethylene, propylene or butylene radical;
e) R6 represents hydrogen or an alkyl radical, especially methyl;
f) X represents hydrogen or an alkyl radical, typically a lower alkyl radical like a Cl to C4 alkyl group, such as a methyl radical; and g) n represents a number of the alkylene oxide groups and may vary from 0 to about 200 or more; for example, from about 2 to 100, such as 2 to 20, to provide phospholipids having, for example, a molecular weight of from 150 to 3000 or more; for example 200 to 2000.
One particular group of phospholipids of the invention prepared by the use of succinic or glutaric anhydride, or other dicarboxylic acids, would be represented by the struc*ural formula:
H

HC -O-R

1 2 I H H ~ H H
HC - 0 - P - 0 - C - C - N - C - ~CH2]m- C - O - (C - C ~ )n ~ X
o wherein m reprcsents a number of 1, 2, 3 or 4.

.

lZ'1~69Z

The polycarboxylic acids used in the preparation of the phospho-lipid compounds are preferably cyclic acids and more particularly cyclic acid anhydride compounds for ease of reaction; for example, C3 to C6 dicarboxylic acids, particularly which form 4-to-7-member-ring anhydrides, such as succinic acid, glutaric acid, adipic acid and phthalic anhydride. Suitable carboxylic acids include, but are not limited to, aliphatic, cycloaliphatic, di and tri carboxylic acids, such as succinic acid, glutaric acidJ glutamic acid, citric acid, tartaric acid, oxalic acid, adipic acid, malic acid, maleic acid, as well as long-chain dicarboxylic acid, although waxy, solid compounds may result from the use of long-chain acids. Preferably the acid compounds employed are the C3 to C7 dicarboxylic acid anhydrides. These novel phospholipid compounds have a distinctly different chemical composition than the compound described, for example, in United States Patents 2,310,679 and 3,085,100, which are products from the coupling of ethylene oxide or similar compounds to crude soy lecithin.
The use of the term "lecithin" describes a number of compounds including lecithin (that is, phosphatidylcholine), a compound that cannot react with ethylene oxide. On the other hand, soy lecithin does contain phos-phatidylethanolamine, phosphatidylinositol and a variety of glycolipids. All of these compounds in crude lecithin can react with ethylene oxide or similar compounds containing a reactive cyclooxide group to form various adducts. For example, in phosphatidyllinositol and with glycolipids, the reactive groups in these molecules are hydroxyl groups which will form an ether linkage, when reacted with ethylene oxide. Phosphatidylethanolamine, which contains a primary amino group, will react with ethylene oxide to form an alkaylamine linkage (see N. Schonfeldt, "Surface Active Ethylene Oxide Adducts", Pergamon Press, 1969). In both cases, these adducts are not biologically degradable, and, therefore, such compounds are undesirable for use in the cosmetic and 6~2 pharmaceutical industries.
The phospholipids of the invention comprise synthetic phospho-lipids in which ~he linkage between the synthetic ethylene oxide or propylene oxide polymer and the naturally occurring phospholipid is a biologically degradable linkage; for example, an amide linkage, which makes these novel phospholipid compounds useful for cosmetic and pharmaceutical uses.
The preparation of the phospholipid compounds is best accomplish-ed by the addition of a cyclic polyacid, particularly anhydride, such as succinic or glutaric acid anhydride, to a polyalkylene oxide polymer. The coupling of the appropriate carboxylic analog of the polyalkylene oxide polymer to the phosphatidylalkanolamine molecule, such as phosphatidylethanolamine, gives the desired compounds. Alternatively, the cyclic acid anhydride can be coupled to the phosphatidylethanolamine, and then the polyalkylene oxide poly-mer is coupled to the modified phospholipid. For example, in one method the low-cost acidic polyalkylene glycol compound can be admixed with crude soy lecithin for a coupling reaction with the phosphatidylethanolamine, and the novel phospholipid compounds extracted with acetone. The acidic polymer may be converted to an acid halide compound, to increase the speed of the reaction.
The acidic polyalkylene glycol polymer compound can be purified further via distillation, ion-exchange chromatography or absorption chromatography. The acyl analog of the polyethylene oxide polymer is activated by a convenient activating agent, such as oxalyl chloride or 1,1 carbonyl diimidazole. The activated carboxylic derivative of the parent polyalkylene oxide polymer is then coupled to the phosphatidylethanolamine via an amide linkage, to form the phospholipid analog compounds of this invention.
The phosphatidylethanolamine either can be isolated from natural sources, synthesized according to established chemical procedures, or enzymati-cally synthesized using the corresponding phosphatidylcholine compound in the presence of ethanolamine and phospholipase D. The reaction of the phosphatidyl-ethanolamine and the carboxylic derivative of the polyalkylene oxide polymer is carried out in an inert solvent. The progress of the reaction can be monitored by thin-layer chromatography. Purification of the final product, if necessary, may be carried out using column chromatography.
In the phospholipid compounds of this invention, the polar-head group of the phosphatidylethanolamine has been modified to alter its physical properties, by the inclusion of a polyalkylene oxide polymer. In all cases where natural phospholipids can be used, such as in drug-delivery systems, in cosmetics, in food, in industrial uses, in treating atherosclerosis, for intra-venous nutrition and other uses, these new synthetic phospholipid compounds can be used alone or in combination with other natural phospholipids, especially phosphatidylcholine. Biologically these synthetic phospholipids will be immuno-logically inert. For example, polyethylene oxide polymers attached to proteins are nonimmunogenic and well tolerated by the body (see Abuchowski et al, J.
Biol. Chem. 252, pp 3578-3581 (1977)~. The covalent linkage between a typical polyalkylene example, such as polyethylene oxide polymer and the phosphatidyl-ethanolamine, is biologically degradable, and phosphatidylethanolamine, itself, is a natural compound.
As a result, these novel compounds have utility in encapsulating drugs, especially water-insoluble drugs, as drug-delivery systems that either can be administered orally or via injection, such as in the encapsulation process disclosed in corresponding United States Patent ~o. 4,320,121 issued March 16, 1982 as well as in the method of United States Patent 4,016,100.
The presence of the hydrophilic alkylene oxide polymer, parti-cularly the polyethylene oxide polymer moiety in the phospholipids, also gives ~ ~ - 6 -12~P~Z
rise to novel and unexpected physical properties in an aqueous environment.
As an example, unsaturated phosphatidylethanolamines, especially those isolated from soybeans, do not form any stable type of structure in water. Phosphatidyl-choline, if hydrated with an aqueous solution, forms large (>2000 A) structure termed multilamellar liposomes. On the other hand, gangliosides have a similar hydrophobic region, compared to phosphatidylethanolamine and phosphatidyl-choline, but the polar region of the ganglioside molecule is composed of hydro-philic oligiosaccharides. The presence of these oligiosaccharides allows the ganglioside to organize into a stable micelle upon hydration with water. sy covalently attaching a hydrophilic polyalkylene polymer, such as polyethylene or polypropylene oxide polymers, to phosphatidylethanolamine, a phospholipid analog to ganglioside is essentially synthesized. It also should be noted that, while no molecular species of phosphatidylethanolamine will form a stable structure in an aqueous environment, the phospholipid analog compounds describ-ed herein do form stable structures upon hydration. As a consequence of this physical behavior, a variety of water-insoluble compounds can be formulated in a stable form in an aqueous environment at physiological pH. Furthermore, the spontaneous structure that these phospholipids form, when hydrated with water from the dry state, is small (less than 200 A; for example, typically average 75 to 100 A), which results in an optically clear solution.
The actual organization of these structures, however, will depend, at least in part, on the selected acyl chain composition of the phos-phatidylethanolamine and the alkylene oxide polymer. In particular, with phosphatidylethanolamine isolated from soybeans and various polyethylene oxide polymers, micellar structures of less than 200 A diameter are spontaneously and easily formed, upon addition of water to the dried phospholipid analog.
These structures are distinct and unique, as compared to liposomes or other lipid vehicles that are composed of phosphatidylcholine.
For the purpose of illustration only, the invention will be des-cribed in connection with the method of preparation and use of certain com-pounds; however, it is recognized that various changes and modifications to the illustrated examples can be made by those persons skilled in the art, all falling within the spirit and scope of the invention.
Example 1. Soy phosphatidylethanolamine succinyl polyethylene glycol mono-- methylether(molecular weight 252) Succinyl polyethylene glycol monomethylether compounds were prepared in accordance with and under the following general method and conditions. 1 mole of the polyethylene glycol polymer was heated with 5 moles of finely divided succinic anhydride in a slurry of CC14 under a nitrogen atmosphere. The solution was magnetically stirred and heated overnight at 75C under a nitrogen atmosphere. Temperature control is important, as the reaction mixture darkens above 75C. Upon cooiing to room temperature, the excess succinic anhydride was removed by filtration. The reaction mixture was then dissolved in a 1:1 methylene chloride/methanol mixture, and sufficient concentrated ~H40H was added, so that an aliquot of the reaction mixture was approximately pH 9, when diluted with water. The succinyl polymer reaction mixture was dissolved in a 95:5:0.8 mixture of methylene chloride/methanol-concentrated NH40H and applied to a silicic acid column equilibrated in the same solvent. The succinyl polymer was eluted with a step gradient of increasing methanol content. The purity of the fraction was monitored by thin-layer chromatography, using a solvent system of 90:10:1 of methylene chloride/methanol-concentrated NH40H. Pure fractions of the succinyl polymer were evaporated to near dryness. Sufficient HCl was added to the mixture, so that an aliquot, when diluted with water, gave a pll of between 2 and 2.5. The compound was then evapora-ted to dryness. r~ethylene chloride was added to the dried material, and any particulate material was filtered off. The filtrate was evaporated to dryness and dried overnight under high vacuum.
The above conditions were used to make the succinyl polyethylene glycol monomethylether, using, as the starting material, polyethylene glycol monomethylether with a molecular weight of 252. To 2200 ~moles of the succinyl polymer compound were added 2000 ~moles of 1,1 carbonyl diimidazole in a benzene solution. The solution was heated at 60C for 10 to 15 minutes, until the bubbling had ceased. This solution was transferred to another flask con-taining 1000 ~moles of dried soy phosphatidylethanolamine (PE), which was prepared by the enzymatic conversion of soy phosphatidylcholine using ethanol-amine and phospholipase D from Savoy cabbage. Sufficient benzene was added to ensure that all of the soy PE had dissolved. Then most of the benzene was removed, leaving a thick slurry. This slurry was stirred with a magnetic stir--rer for approximately 6 hours at 70C under a nitrogen atmosphere. The extent of the conversion of PE to the desired product was monitored by thin-layer chromatography. The reaction mixture was taken to dryness and then partitioned into a two-phase Folch System, with .2M HCl in the upper phase. The lower phase was extracted four more times with this acidic Folch upper phase, and twice with a .3M NH4 acetate upper phase, to remove the imidazole and excess non-coupled succinyl polymer compound. The lower phase was evaporated to dryness.
The sample was dissolved in 95:5:0.8 methylene chloride/methanol-concentrated NH40H and applied to a silicic acid column equilibrated in the same solvent.
The soy PE-succinyl polyethylene glycol monomethylether (molecular weight 252) was eluted with a step gradient of increasing methanol content, while maintain-ing approximately 0.8 to 1.0 concentrated NH40H in the eluting solvent. The elution profile was monitored by thin-layer chromatography, using 80:2:1 Z

methylenc chloride/methanol-concentrated N114011 as the solvent. Pure fractions of the product were pooled and reduced to dryness. The pll was tested and adjusted, if needed, to between 5 and 7. Tlle compound was then dissolved in methylene chloride. The yield of the product was 35% based on the starting soy PE content.
Example 2~ Soy phosphatidylethanolamine succinyl polyethylene glycol mono-methylether ~molecular weight 120) A succinyl polyethylene glycol monomethylether (molecular weight 120) polymer compound was prepared as described in Example 1. 7500 ~moles of the succinyl polyethylene glycol were dissolved in benzene and 4000 ~moles of 1,1 carbonyl diimida~ole were added. The solution was heated at 60C, until all bubbling had ceased. The solution was added to 1000 ~moles of soy PE
that previously had been dried under high vacuum. The reaction conditions were the same as in Example 1. The yield of the pure product, after column chromato-graphy, was 42%.
Example_ . Soy phosphatidylethanolamine succinyl polyethylene glycol mono-methylether ~average molecular weight 1900) A succinyl polyethylene glycol monomethylether (average molecular weight 1900) was prepared as described in Example 1. 1750 ~moles of this com-pound were dissolved in benzene and 1000 ~moles of 1,1 carbonyl diimida~ole were added. The solution was heated to 60C, until the bubbling had ceased.
The solution was added to 483 ~moles oF dried soy PE. The reaction conditions were as described in Example 1. The yield of column-purified material was 44%.
Example 4. Soy phosphatidylethanolamine succinyl polyethylene glycol mono-methylether ~average molecular weight 350) A succinyl polyethylene glycol monomethylether (average molecular weight 350) was prepared as described in Example 1. 7000 ~moles of succinyl 12~(~692 polyethylene glycol monomethylether compound were dissolved in benzene and 4000 ~moles of 1,1 carbonyl diimidazole were added. The solution was heated at 60C, until the bubbling had ceased. This solution was added to 1050 ~moles of dried soy PE. The reaction conditions to form the product were the same as described in Example 1. The yield of the pure product, after column chromato-graphy, was 70%.
Example 5. Soy phosphatidylethanolamine succinyl polyethylene glycol mono-methylether (average molecular weight 750) A succinyl polyethylene glycol monomethylether (average molecular weight 750) was prepared as described in Example 1. 7500 ~moles of the com-pound were dissolved in benzene and 5000 ~moles of l,l carbonyl diimidazole were added. The solution was heated at 60C, until bubbling had ceased. This solution was then added to 1200 ~moles of dried soy PE. The reaction conditions were then as described in Example 1. The yield of the column-purified product was 52%.
Example 6. Soy phosphatidylethanolamine succinyl polyethylene glycol mono-methylether (average molecular weight 550) A succinyl polyethylene glycol monomethylether (average molecular weight 550) was prepared as described in Example l. 3070 ~moles of the com-pound were dissolved in benzene and 2000 ~moles of l,l carbonyl diimidazole were added. The solution was heated at 60C, until the bubbling ceased. The solution was added to 1127 ~moles of dried soy PE. The reaction conditions were the same as described in Example 1. The yield of the column-purified material was 58%.
Exam~le 7. Soy phosphatidylethanolamine succinyl polyethylene glycol mono-methylether (molecular weight 252) Another method of producing the compounds of the invention is the Z

coupling of succinic anhydride to soy PE and then reacting the modified PE with the appropriate polyethylene glycol polymer. Succinic anhydride (1000 ~moles) was reacted with 1000 ~moles of soy PE in a methylene chloride slurry under a nitrogen atmosphere at 70C overnight. The unreacted succinic anhydride was filtered off. The methylene chloride was evaporated and the succinic acid modified PE was purified by column chromatography. 500 ~moles of the succinic acid modified PE was dissolved in benzene, and 500 moles of 1,1 carbonyl di-imidazole were added. The solution was heated at 60C, until the bubbling had ceased. 750 ~moles of the polyethylene glycol monomethylether ~molecular weight 252) were added to the solution, and the mixture was heated for 3 hours under a nitrogen atmosphere at 70C. The purified product was then recovered as described in Example 1.
Example 8. Soy phosphatidylethanolamine suffinyl tetraethylene glycol (molecular weight 194) The soy PE succinic acid derivative was prepared as described in Example 7. 650 ~moles of the compound were dissolved in benzene and 650 ~ moles of 1,1 carbonyl diimidazole were added. The solution was heated at 60C, until bubbling had ceased. To the solution were added 650 ~moles of tetraethylene glycol. The mixture was heated at 70C under a nitrogen atmosphere for 3 hours.
The purified product was recovered as described in Example 1. The yield of the column-purified material was 37%.
Example 9. Soy phosphatidylethanolamine glutaryl polyethylene monomethylether (molecular weight 252) One of the disadvantages of using the succinic anhydride as a linking agent is the high melting point of the anhydride that prevents a homogeneous reaction mixture. In using glutaric anhydride, many of these disadvantages can be addressed. In particular, 1 mole of the polyethylene g~ycol was heated wlth ~ - 12 -lZ~6g2 2 to 3 moles of the glutaric anhydride in a N2 atmosphere at 75C in the absence of any solvent. At the end of the reaction as determined by thin-layer chromatography, the reaction mixture was dissolved in methylene chloride/
methanol 1:1 (v/v) and recovered as described for the succinyl material as described in Example 1. In this particular example, 7.5 g of polyethylene gly-col monomethylether (molecular weight 252) and 5 g of glutaric anhydride were placed in a reaction vessel and heated to 75C, with magnetic stirring, for 3 .. hours under a N2 atmosphere. The glutaryl polyethylene glycol compound was purified by column chromatography. 1200 ~moles of 1,1 carbonyl diimidazole were added to 1500 ~moles of the glutaryl polyethylene glycol compound dissolved in benzene. The solution was heated at 60C, until the bubbling had ceased.
This solution was added to 1127 ~moles of dry soy PE, and the reaction mixture was heated for 3 hours at 70C. The mixture was extracted and purified as described in Example 1. The yield of pure product was 67%.
Examples 10-14 illustrate that the phospholipids of the invention and the parent application are useful in solubilizing water-insoluble drugs, oils and fragrances, to provide aqueous solutions.
Example 10.
The anticancer drug, Taxol (trade mark for an experimental drug of the National Cancer Institute which inhibits the ability of cells to divide), is insoluble in water. 8 ~moles of Taxol (6.5 mg) were dissolved in methylene chloride with 72 ~moles of soy phosphatidylethanolamine succinyl polyethylene glycol monomethylether (average molecular weight 550). The solution was taken -- to dryness and pumped on by a high vacuum. The dried material was hydrated with 1 ml of 10 mM Tris(pH 8.5) and vortexed at room temperature. The resulting solution was optically clear. The solution was then adjusted with concentrated dextrose to bring the dextro5econcentration to 0.3M; thus making the sample ~de (~ k -13 -~ g ~

lZ~ 9Z
suitable for intravenous injection.
Example 11.
Pentobarbital is a barbituate that is insoluble in water at physiological p}l as the acid form. It is the water-insoluble form that exerts its therapeutic activity. ~ standard solution sodium pentobarbital is stable only at high pH and was adjusted with dilute HCL to pH 3. The precipitated pentobarbital was removed by filtration. 40 ~moles of the pentobarbital were dissolved in methylene chloride with 60 ~moles of the soy phosphatidylethanol-amine succinyl polyethylene glycol monomethylether (molecular weight 252).
The solution was taken to dryness and then pumped on by high vacuum. The dried material was hydrated with 2 ml of 10 m\l Tris (pH 8.5), to form an optical-ly clear solution. The solution was adjusted with concentrated dextrose to give a .3~1 solution suitable for intravenous injection.
Example 12.
The anticancer drug, hexamethylmelamine, is water-insoluble. 2 mg of hexamethylmelamine and 70 ~moles of soy phosphatidylethanolamine succinyl polyethylene glycol monomethylether (average molecular weight 550) were dissolv-ed in methylene chloride. The solution was taken to dryness and then pumped on by high vacuum. The solution was hydrated with 1 ml of 10 m~l Tris (pH 8.5), to give an optically clear solution. The solution was adjusted with concen-trated dextose to give a final dextose concentration of 0.3~1 suitable for intra-venous injection.
Example 13.
Another unique property of the phospholipids of the parent application and of this invention is their ability to act as exceedingly power-ful surfactants for cosmetic ingredients, such as oils and petroleum jelly. As an illustration of such ability, 1.6 g of petroleum jelly and 160 mg of soy ~ - 14 -lZ~692 phosphatidylethanolamine succinyl polyethylene glycol monomethylether (molecular weight 252) were dissolved in hexane and taken to dryness and pumped on at high vacuum. To the dried material were added 4 ml of 10 mM Tris ~pH 8.5).
The hydrated solution was then sonicated with a Branson W-375 sonifier at 40C
for 2 minutes. The resulting solution was opaque, but had excellent flow characteristics. When applied to the skin, there was an immediate and notice-able cooling sensation, due to the evaporation of water, and a pleasing tactile sensation.
Example 14.
Another example of the use of the compounds of the invention in the cosmetic field is the solubilization of water-insoluble fragrance oils in an aqueous environment. For example, .250 ml of a fragrance oil and 200 ~moles of soy phosphatidylethanolamine glutaryl polyethylene glycol monomethylether (molecular weight 252) were dissolved i31 0.5 ml of ethanol. The solution was then diluted with 40 ml of water. The resulting solution was optically clear and retained the fragrance aroma.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A synthetic phospholipid having the structural formula:

wherein R1 and R2 each represent hydrogen or an organic acyl radical; R3 represents a C2 to C4 alkylene radical; R4 represents a C2 to C10 alkylene radical; R5 represents an organic linking radical; R6 represents hydrogen or a lower alkyl radical; X represents hydrogen or an alkyl radical; and n represents a number of from 0 to 200.

2. The phospholipid compound of claim 1 wherein R1 and R2 represent C2 to C20 fatty-acid radicals.

3. The phospholipid compound of claim 1 wherein R5 represents a poly-methylene radical.

4. The phospholipid compound of claim 3 wherein R5 represents a C1 to C4 methylene radical.

5. The phospholipid compound of claim 1 wherein n represents a number of from 2 to 100.

6. The phospholipid compound of claim 1 wherein R1 and R2 are organic radicals derived from soybeans.

7. The synthetic phospholipid compound which is a phosphatidyl-ethanolamine succinyl polyethylene glycol compound.

8. The synthetic phospholipid compound which is a phosphatidyl-ethanolamine glutaryl polyethylene glycol compound.

9. The synthetic phospholipid compound having the struc-tural formula:

wherein R1 and R2 represent C2 to C20 hydrocarbon organic acyl radicals; X represents hydrogen or a methyl radical; m represents a number of from 1 to 4; and n represents a number of from 0 to 200.

10. A method of preparing a phosphatidylalkanolamine poly-carboxyl polyalkylene glycol compound, which method comprises reacting a phosphatidylalkanolamine, a polycarboxylic acid and a polyalkylene glycol, wherein the polycarboxylic acid is first reacted with either the polyalkylene glycol or the phosphatidyl-alkanolamine, and the reaction product is subsequently reacted with the remaining component.

11. The method of claim 10 which comprises:
a) reacting a dicarboxylic acid anhydride with a poly C2 to C3 alkylene glycol, to form the carboxyl poly C2 to C3 alkylene glycol compound; and thereafter, b) reacting the carboxyl poly C2 to C3 alkylene glycol compound with a phosphatidylethanolamine.

12. The method of claim 10 wherein the polyalkylene glycol is polyethylene glycol having a molecular weight of from about 150 to 3000.

13. The method of claim 10 wherein the polycarboxylic acid comprises a C2 to C7 dicarboxylic acid anhydride.

14. The method of claim 10 wherein the phosphatidylalkano-lamine is phosphatidylethanolamine.

15. The method of claim 14 wherein the phosphatidylethanolamine is derived from crude soy lecithin.

16. The method of claim 10 which includes recovering the phosphatidyl-alkanolamine polycarboxyl polyalkylene glycol by extracting with acetone.

17. The method of claim 10 which comprises:
a) reacting a dicarboxylic acid anhydride with a phosphatidyl-ethanolamine, to form the phosphatidylethanolamine carboxylic acid compound;
and, thereafter, b) reacting the phosphatidylethanolamine carboxylic acid com-pound with a C2 to C3 polyalkylene glycol.

18. The method of claim 11 wherein the dicarboxylic acid is succinyl acid anhydride or glutaric acid anhydride.

19. A method of solubilizing, in an aqueous environment, a water-insoluble compound, which method comprises admixing a solubilizing amount of a hydrated compound of claim 1 with water and a water-insoluble compound.

20. An aqueous composition, which composition comprises water, a micelle-forming amount of the synthetic phospholipid of claim 1 and a water-insoluble compound.

21. The aqueous composition of claim 20, which solution has micelles therein of less than 200 Angstroms in size.

22. The aqueous composition of claim 20 which comprises a therapeutic drug as the water-insoluble compound.

23. The aqueous composition of claim 20 which comprises a petroleum jelly as the water-insoluble compound.

24. The aqueous composition of claim 20 which comprises a fragrance oil as the water-insoluble compound.

25. The aqueous composition of claim 20 wherein the synthetic phospholipid comprises a soy phosphatidylethanolamine dicarboxyl polyethylene glycol.

26. The phospholipid compound of claim 1 wherein R4 represents an ethylene radical.

27. The phospholipid compound of claim 1 wherein R3 represents an ethylene radical.

28. The phospholipid compound of claim 1 wherein R6 represents a methyl radical.

29. The phospholipid compound of claim 1 wherein the molecular weight is from about 150 to 3000.

30. The synthetic phospholipid compound which is a phosphatidylethanol-amine di or tri carboxyl polyethylene or polypropylene glycol compound.

31. The synthetic phospholipid compound of claim 30 wherein the compound is a polyethylene or polypropylene monomethyl ether compound.

32. The synthetic phospholipid compound of claim 30 wherein the carboxyl is a C3-C6 carboxyl.

33. The synthetic phospholipid compound soy phosphatidylethanolamine succinyl polyethylene glycol monomethyl ether.

34, The synthetic phospholipid compound soy phosphatidyl-ethanolamine glutaryl polyethylene glycol monomethyl ether.

35. The synthetic phospholipid compound of claim 1 which comprises a fatty acid phosphatidylethanolamine succinyl or glutaryl polyethylene glycol compound.