WO2022249105A1 - Methods for the solubilisation of usnic acid, and for the preparation of solutions comprising the same - Google Patents

Methods for the solubilisation of usnic acid, and for the preparation of solutions comprising the same Download PDF

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Publication number
WO2022249105A1
WO2022249105A1 PCT/IB2022/054912 IB2022054912W WO2022249105A1 WO 2022249105 A1 WO2022249105 A1 WO 2022249105A1 IB 2022054912 W IB2022054912 W IB 2022054912W WO 2022249105 A1 WO2022249105 A1 WO 2022249105A1
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WIPO (PCT)
Prior art keywords
solution
usnic acid
cyclodextrin
usnic
rpm
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PCT/IB2022/054912
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French (fr)
Inventor
Giorgio Stefano CERANA
Peter Bos
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Vestatis Gmbh
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Application filed by Vestatis Gmbh filed Critical Vestatis Gmbh
Priority to EP22732640.2A priority Critical patent/EP4346415A1/en
Publication of WO2022249105A1 publication Critical patent/WO2022249105A1/en

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    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01N—PRESERVATION OF BODIES OF HUMANS OR ANIMALS OR PLANTS OR PARTS THEREOF; BIOCIDES, e.g. AS DISINFECTANTS, AS PESTICIDES OR AS HERBICIDES; PEST REPELLANTS OR ATTRACTANTS; PLANT GROWTH REGULATORS
    • A01N43/00—Biocides, pest repellants or attractants, or plant growth regulators containing heterocyclic compounds
    • A01N43/02—Biocides, pest repellants or attractants, or plant growth regulators containing heterocyclic compounds having rings with one or more oxygen or sulfur atoms as the only ring hetero atoms
    • A01N43/04—Biocides, pest repellants or attractants, or plant growth regulators containing heterocyclic compounds having rings with one or more oxygen or sulfur atoms as the only ring hetero atoms with one hetero atom
    • A01N43/06—Biocides, pest repellants or attractants, or plant growth regulators containing heterocyclic compounds having rings with one or more oxygen or sulfur atoms as the only ring hetero atoms with one hetero atom five-membered rings
    • A01N43/12—Biocides, pest repellants or attractants, or plant growth regulators containing heterocyclic compounds having rings with one or more oxygen or sulfur atoms as the only ring hetero atoms with one hetero atom five-membered rings condensed with a carbocyclic ring
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01P—BIOCIDAL, PEST REPELLANT, PEST ATTRACTANT OR PLANT GROWTH REGULATORY ACTIVITY OF CHEMICAL COMPOUNDS OR PREPARATIONS
    • A01P1/00—Disinfectants; Antimicrobial compounds or mixtures thereof
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M13/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment
    • D06M13/10—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen
    • D06M13/144—Alcohols; Metal alcoholates
    • D06M13/148—Polyalcohols, e.g. glycerol or glucose
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M13/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment
    • D06M13/10—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen
    • D06M13/152—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen having a hydroxy group bound to a carbon atom of a six-membered aromatic ring
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M16/00—Biochemical treatment of fibres, threads, yarns, fabrics, or fibrous goods made from such materials, e.g. enzymatic

Definitions

  • the present invention relates to a method for making a usnic acid, or a salt thereof, preferably of plant origin, soluble in water. Furthermore, the present invention relates to a process for preparing a solution of usnic acid, or a salt thereof, preferably an aqueous, stable and well-storable solution of usnic acid, or a salt thereof, preferably said acid, or a salt thereof, being of plant origin. Furthermore, the present invention relates to the use of said usnic acid, or a salt thereof, made soluble by said method, in the textile industry, preferably for the treatment of fabrics, or, for example, for the preparation of an antibacterial and/or antiviral paint or an antibacterial and/or antiviral formulation for a nasal spray.
  • Usnic acid is a dibenzofuran derivative naturally present in some lichen species. Under normal conditions (T 25°C and P 1 Atmosphere), usnic acid is a solid, bitter, yellow substance. It occurs naturally in both dextrorotatory (D+) and levorotatory (L-) forms, as well as a racemic compound.
  • a usnic acid may have the following characteristics: (+)-Usnic acid, EC number 231-456-0, CAS number 7562-61-0, Molecular formula C18H1607, Molar mass 344.3 g/l, Physical state solid at 20°C and 1 Atm pressure, Colour yellow, Melting point 201-202°C, Density 1.54 g/cm 3 at 20°C, Insoluble in water.
  • Usnic acid is non-toxic and it is used in some slimming products.
  • the Applicant following intensive research and development activity, has developed a new specific technology/methodology for increasing the solubility of usnic acid, or a salt thereof, said increase in solubility enabling usnic acid, or a salt thereof, or a solution thereof, preferably an aqueous solution thereof, to be used in the treatment of a fabric so as to impart to the latter an antibacterial and/or antiviral activity that is persistent and long-lasting.
  • Said increase in solubility of usnic acid, or a salt thereof also makes it possible to obtain a solution, preferably an aqueous solution, useful for preparing, for example, an antibacterial and/or antiviral paint, or, for example, an antibacterial and/or antiviral formulation for a nasal spray.
  • Figure 1 and 1 A Examplary image of a thermostatable powder mixer, 1(A) powder mixer container.
  • Figure 2 Data sheet of analysis of a sample of usnic acid micronised by the method according to the present invention.
  • Figure 3 Optical microscopy image of a sample of usnic acid according to the present invention.
  • FIGS 4 and 5 Data sheet of analysis of samples of usnic acid micronised by the method according to the present invention.
  • Figure 6 Data sheet of micronised usnic acid according to the present invention.
  • solubilising usnic acid, or a salt thereof, in water makes it possible, for example, to apply the aqueous solution, containing the usnic acid in solution, to a fabric (impregnation of a fabric, or a thread or a yarn for fabrics) so as to make the latter antibacterial and/or antiviral because the usnic acid is uniformly distributed on the fabric where it is actually dispersed on the fabric (both on the surface and deep within the fabric) in a homogeneous manner and without having modified or degraded it. Furthermore, usnic acid solubilised in this way, and applied on the fabric, is completely available and effective in performing its antibacterial and antiviral action.
  • cyclodextrins e.g., alpha-cyclodextrins, beta-cyclodextrins and/or gamma-cyclodextrins
  • cyclodextrins make water compatible with usnic acid, or a salt thereof.
  • Cyclodextrins perform the function of compatibilizers.
  • usnic acid or simply usnic acid, is understood to include D(+) or L(- ) usnic acid or a mixture thereof in different proportions or a racemic or racemic mixture or racemate (50% D(+) and 50% L(-), as such or in the form of a salt thereof, for example the sodium salt of usnic acid.
  • the present invention also relates to a method for the preparation of an aqueous solution using cyclodextrins, for example, beta-cyclodextrins.
  • the method comprises the following steps.
  • usnic acid, or a salt thereof (D(+) and/or L(-), or mixtures, or racemate) is prepared in a solid form, preferably a powder, even more preferably a micronised powder, having a well determined PSD (Particle Size Distribution) value [Studies in Surface Science and Catalysis; Elsevier, Volume 128, 2000, Pages 633-642; Comparison of Specific Surface Areas of a Micronized Drug Substance as Determined by Different Techniques; M. Sautel, H. Elmaleh, F. Leveiller; https://doi.org/10.1016/S0167-2991 (00)80069- 5Get],
  • PSD D50 The particle distribution, as reported in the present context, is understood to be a PSD D50.
  • the value of PSD D50 is from 1 micron to 50 microns, preferably from 5 microns to 40 microns, even more preferably from 10 microns to 20 microns, e.g. PSD D50: 1, or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 11, or 12, or 13, or 14, or 15, or 16, or 17, or 18, or 19, or 20, or 25, or 30, or 35 or 40 microns.
  • the particles described herein have a PSD ⁇ 10 microns, preferably from 2 to 8 microns, or from 3 to 5 microns). These dimensions can be achieved by a micronisation process.
  • Micronisation is a milling operation, performed by a microniser, in which the material to be processed, usnic acid in this case, must be reduced to extremely fine particles; this process uses the speed and high pressure released by the nitrogen to produce a series of shocks that reduce the particles to particle sizes of less than 10 microns. It is important in micronisation to achieve particle size constancy, ensuring a high/pharmaceutical standard.
  • An air/nitrogen mixture can be used as process gas, e.g. air/nitrogen 1:1, or 1:2, or pure nitrogen, which, due to its inert properties, allows even finely divided powders to be safely processed.
  • different types of techniques can be used to micronise powders. However, mechanical mills are preferred. For example, ball mills, jet mills, hammer mills or pin mills can be used.
  • Ball mills micronise material by agitating it in a vessel with steel or ceramic balls or other means.
  • the technique also serves as an intensive mixing technique capable of producing co-micronised pharmaceutical-excipient mixtures, comprising amorphous drug forms mixed with hydrophilic excipients suitable at the molecular level. This type of mills can be advantageously used in the present context.
  • jet mills Another type of mechanical mills, preferred in the present context, are jet mills.
  • Jet mills can mill materials with particle sizes in the single-digit micron range in a single pass, increasing yield and operating efficiency.
  • the mill injects compressed air at high speed into a chamber where a speed-controlled feeder adds the raw materials.
  • a speed-controlled feeder adds the raw materials.
  • the particles accelerate and collide with each other and with the walls of the milling chamber at high speed.
  • Particle size reduction occurs through a combination of impact and friction. Impacts result from collisions between the fast-moving particles and between the particles and the milling chamber wall. Friction occurs on the surfaces of the particles when the particles move rapidly against each other, causing a shear force that can break the particles.
  • micronising techniques are used, such as jet mills, which create fine particles with a narrow PSD.
  • a jet mill which can be used in the present context, cools the temperature of the air leaving the jets to about -200°F due to the Joule-Thomson effect, and the product leaves the mill no hotter than the air used for milling.
  • the heat generated by the friction of collisions between particles and between particles and walls is counterbalanced by the cooling effect of the expanding air. This allows dry milling of a wider range of materials, especially the more delicate and heat-sensitive ones.
  • jet mills can be used to obtain micronised powders with an average particle size from 1 to 10 microns with a very narrow particle distribution.
  • jet mills can be used in the present context to mix powders and thus obtain a micronised, homogenous mixture at the outlet.
  • a mixture comprising or, alternatively, consisting of said usnic acid and a cyclodextrin is introduced into a container ( Figure 1A) of a powder mixer ( Figure 1), the latter having one or more openings, heating or cooling means, stirring and mixing means, for example mechanical stirring and mixing means, and means for creating a vacuum or a pressurised environment with P greater than 1 Atmosphere.
  • the mixture is a solid mixture comprising usnic acid, for example, having a PSD D50 value from 1 to 10 microns, or from 2 to 8 microns, or from 3 to 5 microns, measured by optical microscopy techniques, or dynamic light scattering (DLS).
  • the mixture is a solid mixture comprising, in addition to said usnic acid, a cyclodextrin in a solid form, for example a powder, preferably a beta-cyclodextrin.
  • Beta-cyclodextrins are in form of a free-flowing, non-packed powder, which can be dried at 60°C for 12 hours in a ventilated oven before mixing.
  • Table 1 the technical specifications for a type of beta-cyclodextrin that can advantageously be used in the present context.
  • said solid mixture comprising or, alternatively, consisting of a usnic acid and a cyclodextrin, e.g. a beta- cyclodextrin
  • a cyclodextrin e.g. a beta- cyclodextrin
  • the cyclodextrin powder is introduced in an excess amount from 1% to 20% by weight, preferably from 5% to 10% by weight.
  • the usnic acid and the cyclodextrin are present in a weight ratio (usnic acid:cyclodextrin) from 1:5 to 1:4, preferably from 1:3 to 1:2, even more preferably from 1:2 to: 1.5, for example 1:1.10 or 1:1.20.
  • the mixer container such as that in Figure 1A, is equipped with rotation means for allowing the mixture, previously introduced, to mix its ingredients/components, and heating and cooling means for performing heating and cooling temperature curves, and means for creating a vacuum (P ⁇ 1 Atmosphere) or a pressurised environment (P> 1 Atmosphere).
  • the container is also equipped with a closure system for its main opening such that it is hermetically sealed and, therefore, capable of maintaining a pressure greater than 1 Atm or even lower than 1 Atm (vacuum).
  • said container containing said usnic acid, or a salt thereof, in powder form and said cyclodextrin powder, is made to rotate (stirring as a whole) by means of rotating means.
  • the container is rotated in such a way that its contents (mixture of usnic acid or a salt thereof and cyclodextrin) are mixed in a slow, gradual and uniform manner (avoiding stratification) over a period of time from 1 hour to 16 hours, preferably from 2 hours to 12 hours, even more preferably from 4 hours to 10 hours, e.g. 8 hours.
  • the container is rotated at a speed from 5 rpm to 50 rpm, preferably from 10 rpm to 40 rpm, even more preferably from 15 rpm to 30 rpm, for example 25 rpm.
  • the container in a stationary position, is charged by introducing, from its inlet opening, said usnic acid, or a salt thereof, and said cyclodextrin at an ambient temperature of about 20°C and a pressure of 1 Atm. Then, the container is rotated allowing the mixture therein, comprising or, alternatively, consisting of usnic acid, or a salt thereof, and the cyclodextrin, to mix uniformly and homogeneously, to give a uniform and homogeneous mixture.
  • the container is rotated slowly for at least 1 hour, preferably for at least 2 hours, even more preferably from 4 to 10 hours, for example from 6 to 8 hours, alternating, every two hours, heating phases at a temperature from 40°C to 80°C, preferably from 50°C to 70°C, for example at 55°C, 60°C, 65°C with vacuum phases of the container, always keeping the mixture in slow and uniform rotation.
  • the previously obtained homogeneous and uniform mixture is poured into water, preferably demineralised water, at a concentration ranging from 0.01% to 5%, preferably from 0.5% to 3.5, even more preferably from 1% to 2%, for example 1.5% w/w in water.
  • the water preferably demineralised water
  • mixing is carried out, this time very vigorously, of the type carried out with a turbomixer in order to achieve a strong mixing of the ingredients in the solution.
  • the mixing is continued for a time from 5 to 60 minutes, preferably from 10 to 40 minutes, even more preferably from20 to 30 minutes.
  • Said high-speed mixing may be carried out at a speed of from 500 rpm to 5,000 rpm, preferably from 1,000 rpm to 3,000 rpm;
  • mixing is carried out in the presence of an ultrasonic bath from 20 KHz to 60 KHz, preferably from 30 KHz to 50 KHz, even more preferably from 35 KHz to 45 KHz, for example at 40 KHz, so as to increase the vibrational agitation of the powders.
  • an ultrasonic bath from 20 KHz to 60 KHz, preferably from 30 KHz to 50 KHz, even more preferably from 35 KHz to 45 KHz, for example at 40 KHz, so as to increase the vibrational agitation of the powders.
  • a filtration phase is performed using a filter with a mesh size ranging from 10 to 100 microns, preferably from 20 to 80 microns, even more preferably from 40 to 60 microns, e.g. 50 microns, to enable even small agglomerates to be filtered out that could complicate the industrial phase of dispersion of the active in or on the target matrix.
  • RLU Relative Light Unit
  • the aqueous solution obtained above, containing the mixture comprising or, alternatively, consisting of usnic acid and cyclodextrins, preferably beta-cyclodextrins, is ready to be added into fabric impregnation production processes (dyeing), for example an impregnation carried out in a foulard tank.
  • fabric impregnation production processes for example an impregnation carried out in a foulard tank.
  • certain additives can be added to the resulting solution to fix or cling the usnic- cyclodextrins compound to the fabric.
  • the methods, equipment and operating conditions used to impregnate fabrics are those known to the person skilled in the textile field.
  • solution object of the present invention can easily be used in conventional industrial plants which would therefore not require any changes or modifications or additions to the process; such processes can reach temperatures of up to 150°C-190°C in the drying phase; such thermal stresses do not degrade the compound applied to the fabric.
  • textile additives can be added such as dyes, preservatives, dispersing additives (PEG, PEO), pH adjusters, as required.
  • the neutral pH of the applied solution allows application to fabrics without the possibility of chemically attacking the fabric that comes into contact with the solution.
  • the method object of the present invention enables the solubility of usnic acid in water to be increased, thus making it suitable for industrial processes since the active ingredient is well dispersed, homogeneous and the tests performed show antibacterial and/or antiviral efficacy of the treated fabric.
  • aqueous solution is obtained/obtainable by the following method, wherein a usnic acid or a D(+) or L(-) salt thereof, or mixtures thereof, or racemate, soluble in water, is obtained by the following steps:
  • a cyclodextrin preferably a beta-cyclodextrin, in the form of a micronised powder wherein said powder comprises powder particles having an average diameter from 1 micron to 10 microns, preferably from 2 to 8 microns;
  • introducing into an apparatus equipped with mixing means said usnic acid powder prepared in step (i) and said cyclodextrin powder prepared in step (ii), wherein said cyclodextrin powder is introduced in an excess by weight from 1% to 20%, preferably from 5% to 10% by weight;
  • step (iv) slow mixing said powders introduced in step (iii), until a homogeneous mixture is obtained, wherein said slow mixing is performed for a time from 1 hour to 16 hours, and at a speed from 5 rpm to 50 rpm;
  • step (v) introducing said mixture obtained in step (iv) into water, preferably demineralised water, and mixing at high speed, until a homogeneous solution is obtained, wherein said high speed mixing is carried out at a speed from 500 rpm to 5,000 rpm, preferably from 1,000 rpm to 3,000 rpm
  • step (vi) filtering said homogeneous solution obtained in step (v) to give a filtered solution.
  • said preparation step (i) and/or (ii) comprises a micronising step performed by a ball mill.
  • said slow mixing step (iv) is performed by alternating, during mixing, heating steps at a temperature from 40°C to 80°C with vacuum steps.
  • step (v) is performed by mixing the mixture obtained in step (iv) in water for a time from 10 minutes to 40 minutes.
  • One aspect of the present invention relates to increasing the stability and preservation over time of the viscous aqueous solution containing the usnic acid:beta-cyclodextrins complex.
  • Stability also refers to, but it is not limited to, the usnic: beta-cyclodextrins complex
  • preservation also refers to, but it is not limited to, the aqueous solution obtained by the method object of the present invention.
  • stability makes it possible not to have a sediment or degradation of the complex
  • stability makes it possible to avoid, for example, mould formation or an increase in the microbiological load.
  • the stability and preservation values over time may vary depending on the characteristics and technical performance required by the user.
  • the preservation of the viscous aqueous solution containing the usnic:beta- cyclodextrins complex may vary depending on the end product required, be it an antibacterial or antiviral paint for wall application or a nasal spray.
  • the viscous aqueous solution containing the usnic:beta-cyclodextrins complex preferably obtained after filtration (vi) is added with a preservative substance capable of maintaining or reducing the microbial, bacterial and viral load, and also the concentration of moulds and yeasts over time, preferably for a period from 12 to 36 months.
  • the aqueous solution containing the usnic:beta-cyclodextrins complex preferably obtained after filtration (vi) is added with a preservative substance such as, for example, a sodium or potassium sorbate, preferably in an amount from 0.05% to 0.5% by weight, even more preferably in an amount from 0.1% to 0.15% by weight, with respect to the total weight of the solution.
  • a sodium or potassium benzoate may also be used as a preservative substance, either alone or in combination with said sodium or potassium sorbate.
  • a sodium or potassium benzoate may be added, preferably in an amount from 0.05% to 0.5% by weight, even more preferably in an amount from 0.1% to 0.15% by weight, with respect to the total weight of the solution.
  • the pH value of the aqueous solution is preferably altered.
  • the aqueous solution obtained after filtration (vi) has a pH value ranging from about 6.5 to about 7.5, preferably about 7 ⁇ 2.
  • the addition of a sodium or potassium sorbate and/or a sodium or potassium benzoate does not greatly change the pH of the solution, which remains at a pH value from about 6.5 to about 7.5, preferably about 7 ⁇ 2.
  • the aqueous solution added with one or more preservatives is, in turn, added with an acidic substance, such as a weak organic or inorganic acid or a salt thereof, such as citric acid monohydrate or a salt thereof, in an amount from 0.05% to 0.5% by weight, with respect to the total weight of the aqueous solution.
  • an acidic substance such as a weak organic or inorganic acid or a salt thereof, such as citric acid monohydrate or a salt thereof
  • the aqueous solution having a pH value preferably from 4 to 5 is stable and remains well-preserved for a period of time from 12 to 36 months, at a temperature from 20 to 30 °C, preferably 25 °C.
  • an aqueous solution is obtained which is capable of maintaining or reducing the microbiological component of the aqueous solution to low or very low and constant over time values such that the microbiological characteristics of the aqueous solution are not compromised over time, for example up to 36 months in packaging.
  • the complex involves the presence of usnic acid incorporated into the cyclodextrin, preferably beta cyclodextrin.
  • the process comprises a step whereby a first and a second solution is prepared.
  • the first solution comprises usnic acid in a concentration from 0.01% to 10%, preferably from 0.05% to 5%, even more preferably from 0.1% to 4% w/w, in tetrahydrofuran THF.
  • the first solution is stirred at room temperature of about 20°C with a mechanical stirrer or mixer for a time from 5 to 50 minutes, preferably from 10 to 40 minutes, even more preferably from 20 to 30 minutes.
  • a second solution is prepared based on demineralised water and cyclodextrin, preferably beta cyclodextrin, at a concentration from 0.01% to 10%, preferably from 0.1% to 6%, more preferably from 0.5% to 5%, e.g. 4% w/w, of cyclodextrin in water.
  • the second solution is stirred at room temperature with a mechanical stirrer or mixer for a time from 5 to 50 minutes, preferably from 10 to 40 minutes, even more preferably from 20 to 30 minutes so as to obtain a homogeneous solution.
  • said first and second solutions are mixed together in equal amounts and the resulting mixture is heated to a temperature from 40°C to 80°C, preferably from 50° to 60°C with active ultrasound at a frequency from 10 KHz to 60 KHz, preferably from 30 KHz to 50 KHz, for example about 30KHz, or 40KHz for at least 20 minutes, preferably for at least 30 minutes up to 60 minutes.
  • the resulting solution is high shear mixed for a time from 5 to 20 minutes, preferably from 10 to 15 minutes, while the solution is allowed to cool.
  • it is mixed at a speed from 500 rpm to 5,000 rpm, preferably from 1,000 rpm to 3,000 rpm.
  • the solution After switching off the mixer, at a room temperature of about 20°C, the solution starts to give a separation between the cyclodextrins coupled/complexed with usnic acid, which are heavier and thus at the bottom, and the solution of water-tetrahydrofuran, free un-coupled cyclodextrins and usnic acid, which are lighter, above the deposit of coupled/complexed usnic and cyclodextrins.
  • a separation by extraction is performed between the uncomplexed top, e.g. by suctioning it gently so as not to disturb the complexed substrate below.
  • this gravitational phase separation may not occur, or may occur with lower yield, as the solvent used, preferably THF, has a low molecular weight, which allows this separation between the complexed and non-complexed part to be carried out more efficiently.
  • compositions can clearly be added to the solution to optimise viscosity, pH, performance and process speed.
  • Suitable textile and/or industrial additives can also be added to the solution to optimise the aesthetics, mechanics, or general characteristics of the fabric to be treated.
  • This second procedure is more more time-consuming and costly than the first procedure, but in this case the cyclodextrin no longer acts as a simple excipient or compatibiliser, but becomes an active part of the product that helps or promotes the active itself to permeate the cell membrane of the microorganisms by targeting the usnic to penetrate the cell or microorganism. Therefore, this second process or procedure increases the efficacy of usnic acid.
  • aqueous solution for a nasal spray one can, for example, use (ingredients %)
  • Citric acid monohydrate 0.2 Citric acid monohydrate 0.2.
  • the aqueous solution in the above example exhibits excellent stability values over time as shown in Table 2, where T1 is the stability at 12 months and T3 is the stability at 36 months.

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Abstract

The present invention relates to a method for making a usnic acid, or a salt thereof, preferably of plant origin, soluble in water. Furthermore, the present invention relates to a process for preparing a solution of usnic acid, or a salt thereof, preferably an aqueous, stable and well-storable solution of usnic acid, or a salt thereof, preferably said acid, or a salt thereof, being of plant origin. Furthermore, the present invention relates to the use of said usnic acid, or a salt thereof, made soluble by said method, in the textile industry, preferably for the treatment of fabrics, or, for example, for the preparation of an antibacterial and/or antiviral paint or an an antibacterial and/or antiviral formulation for a nasal spray.

Description

Methods for the solubilisation of usnic acid, and for the preparation of solutions comprising the same
The present invention relates to a method for making a usnic acid, or a salt thereof, preferably of plant origin, soluble in water. Furthermore, the present invention relates to a process for preparing a solution of usnic acid, or a salt thereof, preferably an aqueous, stable and well-storable solution of usnic acid, or a salt thereof, preferably said acid, or a salt thereof, being of plant origin. Furthermore, the present invention relates to the use of said usnic acid, or a salt thereof, made soluble by said method, in the textile industry, preferably for the treatment of fabrics, or, for example, for the preparation of an antibacterial and/or antiviral paint or an antibacterial and/or antiviral formulation for a nasal spray.
Usnic acid is a dibenzofuran derivative naturally present in some lichen species. Under normal conditions (T 25°C and P 1 Atmosphere), usnic acid is a solid, bitter, yellow substance. It occurs naturally in both dextrorotatory (D+) and levorotatory (L-) forms, as well as a racemic compound.
For example, a usnic acid may have the following characteristics: (+)-Usnic acid, EC number 231-456-0, CAS number 7562-61-0, Molecular formula C18H1607, Molar mass 344.3 g/l, Physical state solid at 20°C and 1 Atm pressure, Colour yellow, Melting point 201-202°C, Density 1.54 g/cm3 at 20°C, Insoluble in water. Usnic acid is non-toxic and it is used in some slimming products.
The insolubility of usnic acid, or a salt thereof, for example in water or other organic solvents, severely limits its use in many fields.
Many attempts have been made in recent years to increase the solubility of usnic acid, or a salt thereof, but unfortunately the results have never met the expectations and needs of market players who wanted to transform and process this raw material/ingredient for the preparation of end products.
Therefore, there is still a need for a technology that allows usnic acid, or a salt thereof, to be made soluble preferably in an aqueous solution so as to enable an increased use thereof.
The Applicant, following intensive research and development activity, has developed a new specific technology/methodology for increasing the solubility of usnic acid, or a salt thereof, said increase in solubility enabling usnic acid, or a salt thereof, or a solution thereof, preferably an aqueous solution thereof, to be used in the treatment of a fabric so as to impart to the latter an antibacterial and/or antiviral activity that is persistent and long-lasting. Said increase in solubility of usnic acid, or a salt thereof, also makes it possible to obtain a solution, preferably an aqueous solution, useful for preparing, for example, an antibacterial and/or antiviral paint, or, for example, an antibacterial and/or antiviral formulation for a nasal spray.
It is an object of the present invention a method for obtaining a usnic acid or a D(+) or L(-) salt thereof, or mixtures thereof, or a racemic mixture, soluble in water, having the characteristics as claimed in the appended claims.
It is an object of the present invention a homogeneous solution in water of usnic acid and cyclodextrin, obtainable by said method, having the characteristics as claimed in the appended claims.
It is an object of the present invention a method for preparing a usnic acid/cyclodextrin complex (or in short usnic:cyclodextrins or usnic: beta-cyclodextrins), having the characteristics as claimed in the appended claims.
It is an object of the present invention a usnic acid/cyclodextrin complex, obtainable by said method, having the characteristics as claimed in the appended claims.
It is an object of the present invention a homogeneous solution of usnic acid and cyclodextrin in water, having the characteristics as claimed in the appended claims.
It is an object of the present invention a usnic acid/cyclodextrin complex in a solid form, having the characteristics as claimed in the appended claims.
It is an object of the present invention the use of said solution, or of a solution comprising the usnic acid/cyclodextrin complex (or in short usnic:cyclodextrins or usnic: beta-cyclodextrins), for the antibacterial and/or antiviral treatment of fabrics, having the characteristics as claimed in the appended claims.
It is an object of the present invention the use of an aqueous solution comprising usnic acid and cyclodextrin, or of a solution comprising usnic acid/cyclodextrin complex (or in short usnic:cyclodextrins or usnic:beta-cyclodextrins), for the antibacterial and/or antiviral treatment of fabrics, having the characteristics as claimed in the appended claims.
It is an object of the present invention the use of a stable and well-storable aqueous solution comprising usnic acid and cyclodextrin, or of a solution comprising usnic acid/cyclodextrin complex (or in short usnic:cyclodextrins or usnic:beta-cyclodextrins) for the preparation of an antibacterial and/or antiviral paint preferably for wall applications, or for the preparation of an antibacterial and/or antiviral formulation for nasal spray, having the characteristics as claimed in the appended claims.
Brief description of the figures
Figure 1 and 1 A: Examplary image of a thermostatable powder mixer, 1(A) powder mixer container.
Figure 2: Data sheet of analysis of a sample of usnic acid micronised by the method according to the present invention.
Figure 3: Optical microscopy image of a sample of usnic acid according to the present invention.
Figures 4 and 5: Data sheet of analysis of samples of usnic acid micronised by the method according to the present invention.
Figure 6: Data sheet of micronised usnic acid according to the present invention.
Preferred embodiments of the present invention are shown below by way of example and, therefore, not limiting the scope of the invention.
In a first embodiment, the Applicant has developed a technology/method that allows to increase the solubility of usnic acid, or a salt thereof, normally in a solid form, and insoluble at 20°C and P=1 Atm, to make it usable in a solution form, preferably in an aqueous solution, to treat fabrics.
The possibility of solubilising usnic acid, or a salt thereof, in water makes it possible, for example, to apply the aqueous solution, containing the usnic acid in solution, to a fabric (impregnation of a fabric, or a thread or a yarn for fabrics) so as to make the latter antibacterial and/or antiviral because the usnic acid is uniformly distributed on the fabric where it is actually dispersed on the fabric (both on the surface and deep within the fabric) in a homogeneous manner and without having modified or degraded it. Furthermore, usnic acid solubilised in this way, and applied on the fabric, is completely available and effective in performing its antibacterial and antiviral action.
This action occurs because a sort of coating layer of active ingredient (usnic acid or salt thereof) is formed on the fabric, which covers the fabric and is thus able to perform its antibacterial and/or antiviral function. Other applications of said solution may be for the preparation of an antibacterial and/or antiviral paint for applications on wall and/or other surfaces in general, or also for the preparation of an antibacterial or antiviral nasal spray.
In said first embodiment, the use of cyclodextrins (e.g., alpha-cyclodextrins, beta-cyclodextrins and/or gamma-cyclodextrins) makes compatible the formation of an aggregate or compound between usnic acid, or a salt thereof, and water. In practice, cyclodextrins make water compatible with usnic acid, or a salt thereof. Cyclodextrins perform the function of compatibilizers.
In the context of the present invention, usnic acid, or simply usnic acid, is understood to include D(+) or L(- ) usnic acid or a mixture thereof in different proportions or a racemic or racemic mixture or racemate (50% D(+) and 50% L(-), as such or in the form of a salt thereof, for example the sodium salt of usnic acid.
In addition to a method for making usnic acid soluble, the present invention also relates to a method for the preparation of an aqueous solution using cyclodextrins, for example, beta-cyclodextrins.
In an embodiment, the method comprises the following steps.
In a first step, usnic acid, or a salt thereof (D(+) and/or L(-), or mixtures, or racemate) is prepared in a solid form, preferably a powder, even more preferably a micronised powder, having a well determined PSD (Particle Size Distribution) value [Studies in Surface Science and Catalysis; Elsevier, Volume 128, 2000, Pages 633-642; Comparison of Specific Surface Areas of a Micronized Drug Substance as Determined by Different Techniques; M. Sautel, H. Elmaleh, F. Leveiller; https://doi.org/10.1016/S0167-2991 (00)80069- 5Get],
The particle distribution, as reported in the present context, is understood to be a PSD D50. The particle size distribution PSD D50 is also known as the median diameter or mean value of the particle distribution, and is the value of the particle diameter at 50% in the cumulative distribution. It is one of the important parameters characterising particle size. For example, if D50=5.8 pm, then 50% of the particles in the sample are larger than 5.8 pm, and 50% smaller than 5.8 pm. D50 is usually used to represent the particle size of a group of particles.
In an embodiment, the value of PSD D50 is from 1 micron to 50 microns, preferably from 5 microns to 40 microns, even more preferably from 10 microns to 20 microns, e.g. PSD D50: 1, or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 11, or 12, or 13, or 14, or 15, or 16, or 17, or 18, or 19, or 20, or 25, or 30, or 35 or 40 microns. Advantageously, the particles described herein have a PSD < 10 microns, preferably from 2 to 8 microns, or from 3 to 5 microns). These dimensions can be achieved by a micronisation process.
Micronisation is a milling operation, performed by a microniser, in which the material to be processed, usnic acid in this case, must be reduced to extremely fine particles; this process uses the speed and high pressure released by the nitrogen to produce a series of shocks that reduce the particles to particle sizes of less than 10 microns. It is important in micronisation to achieve particle size constancy, ensuring a high/pharmaceutical standard. An air/nitrogen mixture can be used as process gas, e.g. air/nitrogen 1:1, or 1:2, or pure nitrogen, which, due to its inert properties, allows even finely divided powders to be safely processed. In the present context, different types of techniques can be used to micronise powders. However, mechanical mills are preferred. For example, ball mills, jet mills, hammer mills or pin mills can be used.
Ball mills micronise material by agitating it in a vessel with steel or ceramic balls or other means. In addition to the comminution function of ball milling, the technique also serves as an intensive mixing technique capable of producing co-micronised pharmaceutical-excipient mixtures, comprising amorphous drug forms mixed with hydrophilic excipients suitable at the molecular level. This type of mills can be advantageously used in the present context.
Another type of mechanical mills, preferred in the present context, are jet mills.
Jet mills can mill materials with particle sizes in the single-digit micron range in a single pass, increasing yield and operating efficiency. In this micronising method, the mill injects compressed air at high speed into a chamber where a speed-controlled feeder adds the raw materials. As the particles enter the air stream, they accelerate and collide with each other and with the walls of the milling chamber at high speed. Particle size reduction occurs through a combination of impact and friction. Impacts result from collisions between the fast-moving particles and between the particles and the milling chamber wall. Friction occurs on the surfaces of the particles when the particles move rapidly against each other, causing a shear force that can break the particles.
In the present context, micronising techniques are used, such as jet mills, which create fine particles with a narrow PSD. A jet mill, which can be used in the present context, cools the temperature of the air leaving the jets to about -200°F due to the Joule-Thomson effect, and the product leaves the mill no hotter than the air used for milling. The heat generated by the friction of collisions between particles and between particles and walls is counterbalanced by the cooling effect of the expanding air. This allows dry milling of a wider range of materials, especially the more delicate and heat-sensitive ones.
In the present context, jet mills can be used to obtain micronised powders with an average particle size from 1 to 10 microns with a very narrow particle distribution.
Advantageously, jet mills can be used in the present context to mix powders and thus obtain a micronised, homogenous mixture at the outlet.
Next, a mixture comprising or, alternatively, consisting of said usnic acid and a cyclodextrin is introduced into a container (Figure 1A) of a powder mixer (Figure 1), the latter having one or more openings, heating or cooling means, stirring and mixing means, for example mechanical stirring and mixing means, and means for creating a vacuum or a pressurised environment with P greater than 1 Atmosphere. The mixture is a solid mixture comprising usnic acid, for example, having a PSD D50 value from 1 to 10 microns, or from 2 to 8 microns, or from 3 to 5 microns, measured by optical microscopy techniques, or dynamic light scattering (DLS).
The mixture is a solid mixture comprising, in addition to said usnic acid, a cyclodextrin in a solid form, for example a powder, preferably a beta-cyclodextrin.
Beta-cyclodextrins, preferably used in this context, are in form of a free-flowing, non-packed powder, which can be dried at 60°C for 12 hours in a ventilated oven before mixing. Below are the technical specifications for a type of beta-cyclodextrin that can advantageously be used in the present context (Table 1).
Figure imgf000007_0001
Table 1
In said solid mixture comprising or, alternatively, consisting of a usnic acid and a cyclodextrin, e.g. a beta- cyclodextrin, it is important that the cyclodextrin is present in an amount greater than the usnic acid; preferably in an amount greater than at least 5%, e.g. by weight, or at least 10% or 20%. Advantageously, the cyclodextrin powder is introduced in an excess amount from 1% to 20% by weight, preferably from 5% to 10% by weight. In an embodiment, the usnic acid and the cyclodextrin, preferably a beta-cyclodextrin, are present in a weight ratio (usnic acid:cyclodextrin) from 1:5 to 1:4, preferably from 1:3 to 1:2, even more preferably from 1:2 to: 1.5, for example 1:1.10 or 1:1.20.
The mixer container, such as that in Figure 1A, is equipped with rotation means for allowing the mixture, previously introduced, to mix its ingredients/components, and heating and cooling means for performing heating and cooling temperature curves, and means for creating a vacuum (P< 1 Atmosphere) or a pressurised environment (P> 1 Atmosphere). The container is also equipped with a closure system for its main opening such that it is hermetically sealed and, therefore, capable of maintaining a pressure greater than 1 Atm or even lower than 1 Atm (vacuum).
Next, said container, containing said usnic acid, or a salt thereof, in powder form and said cyclodextrin powder, is made to rotate (stirring as a whole) by means of rotating means.
The container is rotated in such a way that its contents (mixture of usnic acid or a salt thereof and cyclodextrin) are mixed in a slow, gradual and uniform manner (avoiding stratification) over a period of time from 1 hour to 16 hours, preferably from 2 hours to 12 hours, even more preferably from 4 hours to 10 hours, e.g. 8 hours. The container is rotated at a speed from 5 rpm to 50 rpm, preferably from 10 rpm to 40 rpm, even more preferably from 15 rpm to 30 rpm, for example 25 rpm.
The container, in a stationary position, is charged by introducing, from its inlet opening, said usnic acid, or a salt thereof, and said cyclodextrin at an ambient temperature of about 20°C and a pressure of 1 Atm. Then, the container is rotated allowing the mixture therein, comprising or, alternatively, consisting of usnic acid, or a salt thereof, and the cyclodextrin, to mix uniformly and homogeneously, to give a uniform and homogeneous mixture.
The container is rotated slowly for at least 1 hour, preferably for at least 2 hours, even more preferably from 4 to 10 hours, for example from 6 to 8 hours, alternating, every two hours, heating phases at a temperature from 40°C to 80°C, preferably from 50°C to 70°C, for example at 55°C, 60°C, 65°C with vacuum phases of the container, always keeping the mixture in slow and uniform rotation.
Fast rotation of the type carried out with a turbomixer is to be avoided as the different specific weights (mass by weight and density) of the two components/ingredients in the mixture contribute to a separation (stratification, or formation of layers), rather than a homogeneous and uniform mixture. The formation of layers, or stratification phenomena, helps to keep the usnic acid separated from the cyclodextrins thus preventing their physical, preferably electrostatic, coupling.
The slow, uniform and homogeneous rotation of the usnic acid and the cyclodextrins, present within the mixture contained within the container, results in friction by physical contact between the usnic acid powder and the cyclodextrin powder, resulting in a strong electrostaticity between the two components/ingredients. The formation of this electrostaticity or charge density allows physical coupling between the usnic acid powder and the cyclodextrin powder by electrostatic attraction.
Subsequently, at the end of the mixing step, the previously obtained homogeneous and uniform mixture is poured into water, preferably demineralised water, at a concentration ranging from 0.01% to 5%, preferably from 0.5% to 3.5, even more preferably from 1% to 2%, for example 1.5% w/w in water.
The water, preferably demineralised water, can be previously heated to a temperature from 40°C to 80°C, preferably from 50°C to 60°C, e.g. at 50°C, before the mixture is added.
Once the addition of the mixture to the heated water is complete, mixing is carried out, this time very vigorously, of the type carried out with a turbomixer in order to achieve a strong mixing of the ingredients in the solution. The mixing is continued for a time from 5 to 60 minutes, preferably from 10 to 40 minutes, even more preferably from20 to 30 minutes.
Said high-speed mixing may be carried out at a speed of from 500 rpm to 5,000 rpm, preferably from 1,000 rpm to 3,000 rpm;
Preferably, mixing is carried out in the presence of an ultrasonic bath from 20 KHz to 60 KHz, preferably from 30 KHz to 50 KHz, even more preferably from 35 KHz to 45 KHz, for example at 40 KHz, so as to increase the vibrational agitation of the powders.
Subsequently, at the end of the mixing phase, a filtration phase is performed using a filter with a mesh size ranging from 10 to 100 microns, preferably from 20 to 80 microns, even more preferably from 40 to 60 microns, e.g. 50 microns, to enable even small agglomerates to be filtered out that could complicate the industrial phase of dispersion of the active in or on the target matrix.
A check carried out with a bioluminometer of the type, e.g. Hygiena Ensure, on the filtered solution should give values equal to or less than those of the demineralised water used at the beginning, preferably optimal values are values from RLU < 30 to RLU > 3, even more preferably from RLU < 20 to RLU > 5, e.g. RLU < 5, or RLU < 10. RLU (Relative Light Unit).
At this point, the aqueous solution obtained above, containing the mixture comprising or, alternatively, consisting of usnic acid and cyclodextrins, preferably beta-cyclodextrins, is ready to be added into fabric impregnation production processes (dyeing), for example an impregnation carried out in a foulard tank. Depending on the type of fabric to be impregnated, and depending on the final application of the impregnated fabric, certain additives can be added to the resulting solution to fix or cling the usnic- cyclodextrins compound to the fabric. The methods, equipment and operating conditions used to impregnate fabrics are those known to the person skilled in the textile field.
It should be noted that the solution object of the present invention can easily be used in conventional industrial plants which would therefore not require any changes or modifications or additions to the process; such processes can reach temperatures of up to 150°C-190°C in the drying phase; such thermal stresses do not degrade the compound applied to the fabric.
Other textile additives can be added such as dyes, preservatives, dispersing additives (PEG, PEO), pH adjusters, as required.
The neutral pH of the applied solution allows application to fabrics without the possibility of chemically attacking the fabric that comes into contact with the solution.
The method object of the present invention enables the solubility of usnic acid in water to be increased, thus making it suitable for industrial processes since the active ingredient is well dispersed, homogeneous and the tests performed show antibacterial and/or antiviral efficacy of the treated fabric.
It is an object of the present invention a stable aqueous solution that can be stored for at least 36 months comprising usnic acid and cyclodextrin and/or a usnic aci d : beta-cy clodextri n complex.
Said aqueous solution is obtained/obtainable by the following method, wherein a usnic acid or a D(+) or L(-) salt thereof, or mixtures thereof, or racemate, soluble in water, is obtained by the following steps:
(i) preparing a usnic acid in the form of a micronised powder, wherein said powder comprises powder particles having an average diameter from 1 micron to 10 microns, preferably from 2 to 8 microns;
(ii) preparing a cyclodextrin, preferably a beta-cyclodextrin, in the form of a micronised powder wherein said powder comprises powder particles having an average diameter from 1 micron to 10 microns, preferably from 2 to 8 microns; (iii) introducing into an apparatus equipped with mixing means said usnic acid powder prepared in step (i) and said cyclodextrin powder prepared in step (ii), wherein said cyclodextrin powder is introduced in an excess by weight from 1% to 20%, preferably from 5% to 10% by weight;
(iv) slow mixing said powders introduced in step (iii), until a homogeneous mixture is obtained, wherein said slow mixing is performed for a time from 1 hour to 16 hours, and at a speed from 5 rpm to 50 rpm;
(v) introducing said mixture obtained in step (iv) into water, preferably demineralised water, and mixing at high speed, until a homogeneous solution is obtained, wherein said high speed mixing is carried out at a speed from 500 rpm to 5,000 rpm, preferably from 1,000 rpm to 3,000 rpm
(vi) filtering said homogeneous solution obtained in step (v) to give a filtered solution.
Preferably, said preparation step (i) and/or (ii) comprises a micronising step performed by a ball mill.
Preferably, said slow mixing step (iv) is performed by alternating, during mixing, heating steps at a temperature from 40°C to 80°C with vacuum steps.
Preferably, said step (v) is performed by mixing the mixture obtained in step (iv) in water for a time from 10 minutes to 40 minutes.
One aspect of the present invention relates to increasing the stability and preservation over time of the viscous aqueous solution containing the usnic acid:beta-cyclodextrins complex.
Stability also refers to, but it is not limited to, the usnic: beta-cyclodextrins complex, while preservation also refers to, but it is not limited to, the aqueous solution obtained by the method object of the present invention. For example, stability makes it possible not to have a sediment or degradation of the complex, while stability makes it possible to avoid, for example, mould formation or an increase in the microbiological load.
In fact, depending on the type of end product to be prepared, e.g. a nasal spray, which will depend on the type of intended application, e.g. antibacterial or antiviral, the stability and preservation values over time may vary depending on the characteristics and technical performance required by the user.
As mentioned above, the preservation of the viscous aqueous solution containing the usnic:beta- cyclodextrins complex may vary depending on the end product required, be it an antibacterial or antiviral paint for wall application or a nasal spray. In an embodiment, the viscous aqueous solution containing the usnic:beta-cyclodextrins complex, preferably obtained after filtration (vi), is added with a preservative substance capable of maintaining or reducing the microbial, bacterial and viral load, and also the concentration of moulds and yeasts over time, preferably for a period from 12 to 36 months.
The aqueous solution containing the usnic:beta-cyclodextrins complex, preferably obtained after filtration (vi), is added with a preservative substance such as, for example, a sodium or potassium sorbate, preferably in an amount from 0.05% to 0.5% by weight, even more preferably in an amount from 0.1% to 0.15% by weight, with respect to the total weight of the solution. Preferably, a sodium or potassium benzoate may also be used as a preservative substance, either alone or in combination with said sodium or potassium sorbate. For example, a sodium or potassium benzoate may be added, preferably in an amount from 0.05% to 0.5% by weight, even more preferably in an amount from 0.1% to 0.15% by weight, with respect to the total weight of the solution. In order to enable the preservative to perform its function to the best of its ability, the pH value of the aqueous solution is preferably altered. In practice, the aqueous solution obtained after filtration (vi) has a pH value ranging from about 6.5 to about 7.5, preferably about 7±2. The addition of a sodium or potassium sorbate and/or a sodium or potassium benzoate does not greatly change the pH of the solution, which remains at a pH value from about 6.5 to about 7.5, preferably about 7±2. The aqueous solution added with one or more preservatives is, in turn, added with an acidic substance, such as a weak organic or inorganic acid or a salt thereof, such as citric acid monohydrate or a salt thereof, in an amount from 0.05% to 0.5% by weight, with respect to the total weight of the aqueous solution. For example, the addition of 0.02% by weight of citric acid monohydrate results in an aqueous solution having a pH value of about 5, while the use of 0.2% by weight of citric acid monohydrate results in an aqueous solution having a pH value of about 4. The aqueous solution having a pH value preferably from 4 to 5 is stable and remains well-preserved for a period of time from 12 to 36 months, at a temperature from 20 to 30 °C, preferably 25 °C. By the addition of said one or more preservative substances to the aqueous solution containing the usnic:beta-cyclodextrins complex, preferably obtained after filtration (vi), an aqueous solution is obtained which is capable of maintaining or reducing the microbiological component of the aqueous solution to low or very low and constant over time values such that the microbiological characteristics of the aqueous solution are not compromised over time, for example up to 36 months in packaging. The addition of said one or more preservative substances in said aqueous solution preferably obtained after filtration (vi) is required because usnic acid and/or a salt thereof is present in the aqueous solution in an amount lower than its MIC. It is an object of the present invention a second process for preparing a solution comprising or, alternatively, consisting of a guest-host complex between usnic acid and cyclodextrins, preferably beta- cyclodextrins.
The complex involves the presence of usnic acid incorporated into the cyclodextrin, preferably beta cyclodextrin.
The process comprises a step whereby a first and a second solution is prepared.
The first solution, solvent-based, comprises usnic acid in a concentration from 0.01% to 10%, preferably from 0.05% to 5%, even more preferably from 0.1% to 4% w/w, in tetrahydrofuran THF.
The first solution is stirred at room temperature of about 20°C with a mechanical stirrer or mixer for a time from 5 to 50 minutes, preferably from 10 to 40 minutes, even more preferably from 20 to 30 minutes.
Next, a second solution is prepared based on demineralised water and cyclodextrin, preferably beta cyclodextrin, at a concentration from 0.01% to 10%, preferably from 0.1% to 6%, more preferably from 0.5% to 5%, e.g. 4% w/w, of cyclodextrin in water.
The second solution is stirred at room temperature with a mechanical stirrer or mixer for a time from 5 to 50 minutes, preferably from 10 to 40 minutes, even more preferably from 20 to 30 minutes so as to obtain a homogeneous solution.
Using an ultrasonic bath, said first and second solutions are mixed together in equal amounts and the resulting mixture is heated to a temperature from 40°C to 80°C, preferably from 50° to 60°C with active ultrasound at a frequency from 10 KHz to 60 KHz, preferably from 30 KHz to 50 KHz, for example about 30KHz, or 40KHz for at least 20 minutes, preferably for at least 30 minutes up to 60 minutes.
Next, the resulting solution is high shear mixed for a time from 5 to 20 minutes, preferably from 10 to 15 minutes, while the solution is allowed to cool. Preferably it is mixed at a speed from 500 rpm to 5,000 rpm, preferably from 1,000 rpm to 3,000 rpm.
After switching off the mixer, at a room temperature of about 20°C, the solution starts to give a separation between the cyclodextrins coupled/complexed with usnic acid, which are heavier and thus at the bottom, and the solution of water-tetrahydrofuran, free un-coupled cyclodextrins and usnic acid, which are lighter, above the deposit of coupled/complexed usnic and cyclodextrins. A separation by extraction is performed between the uncomplexed top, e.g. by suctioning it gently so as not to disturb the complexed substrate below.
Various methods known in the pharmaceutical field can be used to extract the formed usnic-cyclodextrins complex: spray drying, freeze-drying, evaporation or rotational evaporator.
Regardless of the technology used to remove water and solvent from the usnic-cyclodextrins complex, what will be obtained is a powder consisting of the 100% usnio-cyclodextrins complex.
If another solvent is used instead of THF, this gravitational phase separation may not occur, or may occur with lower yield, as the solvent used, preferably THF, has a low molecular weight, which allows this separation between the complexed and non-complexed part to be carried out more efficiently.
Once the complexed part (Guest-Host complex) has been separated, it is possible to redissolve it (dissolve it again) in water either to make drinkable and/or injectable pharmaceutical compounds or solutions, or to make solutions for industrial plants wherein the solution can be sprayed, micronised, coated or applied on a fabric to be treated.
Pharmaceutical and/or industrial process additives can clearly be added to the solution to optimise viscosity, pH, performance and process speed.
Suitable textile and/or industrial additives can also be added to the solution to optimise the aesthetics, mechanics, or general characteristics of the fabric to be treated.
This second procedure is more more time-consuming and costly than the first procedure, but in this case the cyclodextrin no longer acts as a simple excipient or compatibiliser, but becomes an active part of the product that helps or promotes the active itself to permeate the cell membrane of the microorganisms by targeting the usnic to penetrate the cell or microorganism. Therefore, this second process or procedure increases the efficacy of usnic acid.
EXAMPLE
In an embodiment of an aqueous solution for a nasal spray, one can, for example, use (ingredients %)
Purified water 97.50755
Hydroxypropyl methyl cellulose HPCM 0.97
(+) Usnic acid 0.0075
Beta cyclodextrin 0.015 Sodium chloride 0.9
Sodium benzoate 0.15
Potassium sorbate 0.15
Tocotrienols 0.1
Citric acid monohydrate 0.2.
The aqueous solution in the above example exhibits excellent stability values over time as shown in Table 2, where T1 is the stability at 12 months and T3 is the stability at 36 months.
Figure imgf000015_0001
Table 2

Claims

1. A method for obtaining a water-soluble usnic acid or a D(+) or L(-) salt thereof, or mixtures, or racemate, said method comprising the following steps:
(i) preparing a usnic acid in the form of a micronised powder, wherein said powder comprises powder particles having an average diameter from 1 micron to 10 microns, preferably from 2 to 8 microns;
(ii) preparing a cyclodextrin, preferably a beta-cyclodextrin, in the form of a micronised powder wherein said powder comprises powder particles having an average diameter from 1 micron to 10 microns, preferably from 2 to 8 microns;
(iii) introducing into an apparatus equipped with mixing means said usnic acid powder prepared in step (i) and said cyclodextrin powder prepared in step (ii), wherein said cyclodextrin powder is introduced in an excess by weight from 1% to 20%, preferably from 5% to 10% by weight;
(iv) slow mixing said powders introduced in step (iii), until a homogeneous mixture is obtained, wherein said slow mixing is performed for a time from 1 hour to 16 hours, and at a speed from 5 rpm to 50 rpm;
(v) introducing said mixture obtained in step (iv) into water, preferably demineralised water, and mixing at high speed, until a homogeneous solution is obtained, wherein said high speed mixing is carried out at a speed from 500 rpm to 5,000 rpm, preferably from 1,000 rpm to 3,000 rpm
(vi) filtering said homogeneous solution obtained in step (v) to give a filtered solution.
2. The method according to claim 1, wherein said preparation step (i) and/or (ii) comprises a micronisation step performed by a ball mill.
3. The method according to any one of the preceding claims, wherein said slow mixing step (iv) is performed by alternating, during mixing, heating steps at a temperature from 40 °C to 80 °C, with vacuum steps.
4. The method according to any one of the preceding claims, wherein said step (v) is performed by mixing the mixture obtained in step (iv) in water for a time from 10 minutes to 40 minutes.
5. The method according to any one of the preceding claims, wherein the filtered solution obtained from the filtration step (vi) is added with at least one preservative substance, preferably a sodium or potassium sorbate and/or a sodium and potassium benzoate.
6. The method according to claim 5, wherein said at least one preservative substance is added in an amount from 0.05% to 0.5% by weight, even more preferably in an amount from 0.1% to 0.15% by weight, with respect to the total weight of the solution.
7. The method according to any one of the preceding claims, wherein said aqueous solution is added with an acidic substance, preferably a weak organic or inorganic acid or a sodium or potassium salt thereof, even more preferably it is added with a citric acid monohydrate or a salt thereof, in an amount from 0.05% to 0.5% by weight, with respect to the total weight of the aqueous solution.
8. A solution, stable and well-storable up to at least 36 months, homogeneous in water of usnic acid and cyclodextrin obtainable by the method according to any one of the preceding claims.
9. A method for the preparation of a usnic acid/cyclodextrin complex comprising the following steps:
(a) preparing a solution of usnic acid in an aprotic polar solvent, preferably tetrahydrofuran (THF);
(b) preparing an aqueous solution of a cyclodextrin, preferably a beta-cyclodextrin, in water;
(c) introducing said solution prepared in step (a) into said solution prepared in step (b), or said solution prepared in step (b) into said solution prepared in step (a) to obtain a liquid mixture;
(d) subjecting said liquid mixture, obtained in step (c), to a sonication process at a frequency from 10 KHz to 60 KHz, preferably from 30 KHz to 50 KHz, preferably heating at a temperature from 40°C to 80°C;
(e) mixing the liquid mixture obtained from step (d) at high speed, preferably from 5 minutes to 20 minutes at a speed from 500 rpm to 5,000 rpm to obtain a solution comprising a usnic acid/cyclodextrin complex;
(f) extracting the usnic acid/cyclodextrin complex from the initial uncomplexed components and excess solvent.
10. The method according to claim 9, wherein said solution prepared in step (a) has a concentration from 0.05% to 5% w/w of usnic acid in solvent, and wherein said solution prepared in step (b) has a concentration from 0.01% to 10% w/w of cyclodextrin in water.
11. The method according to any one of claims 9-10, wherein said sonication step (d) is performed for a time from 30 minutes to 60 minutes, at a frequency from 30 KHz to 50 KHz.
12. A usnic acid/cyclodextrin complex, obtainable according to the method according to any one of claims 9-11.
13. A homogeneous solution of usnic acid and cyclodextrin in water.
14. A usnic acid/cyclodextrin complex in a solid form.
15. Use of a solution according to claim 8, or a solution comprising the usnic acid/cyclodextrin complex according to claim 13 for antibacterial and/or antiviral treatment of fabrics.
16. Use of an aqueous solution comprising usnic acid and cyclodextrin, or a solution comprising the usnic acid/cyclodextrin complex for antibacterial and/or antiviral treatment of fabrics.
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