Patent Description:
It is of great interest to the pharmaceutical industry to develop improved formulations of active pharmaceutical ingredients (APIs). Formulation can influence the stability and bioavailability of APIs as well as other characteristics. Formulation can also influence various aspects of drug product (DP) manufacture, for example, ease and safety of the manufacturing process.

Many APIs used to prepare DPs are cohesive particles that have poor flowability and readily agglomerate. Excipients, for example, silica, are often added to API particles to improve flowability and other handling characteristics.

Numerous technologies for encapsulating or coating both APIs and DPs have been developed, e.g., polymer mesh coating, pan coating, aerosolized coating, fluidized bed reactor coating, molecular layer deposition coating, and atomic layer deposition coating.

In one aspect, a method of preparing coated particles having an active pharmaceutical ingredient (API)-containing core enclosed by one or more silicon oxide (SiO<NUM>) layers is disclosed. The silicon oxide layer is deposited using a relatively low temperature process (i.e., the temperature of the particles does not exceed <NUM> and is preferably between <NUM> and <NUM> during the entire deposition process) without the use of a catalyst, e.g., without the use of an amine catalyst. The silicon oxide coating is conformal and pin-hole free. The process can be used to coat particles that consist of APIs; particles that comprise one or more APIs and one or more excipients; and particles that consist of APIs and one more excipients, for example, particles of an amorphous solid dispersion of one or more APIs and one or more excipients. After the silicon oxide layer is deposited, a polymer layer can be applied by molecular layer deposition (MLD) or hybrid ALD/MLD deposition. These steps can be repeated to create particles having an API-containing core enclosed by multiple layers (e.g., multiple alternating layers) of silicon oxide and polymer.

The silicon oxide layer is thin and conforms to the API-containing core. This layer can greatly improve the flowability and other handling characteristics of the API-containing core. The coating layer can adjust the dissolution rate of the API, such as for extended release coating, an enteric coating and can increase the stability of the API, e.g., can increase resistance to oxidation and/or alteration in crystalline form. Thus, the coating layers can reduce transition of the API form an amorphous form to a crystalline form. The coating layers can provide bulking and/or improve compressibility thereby reducing the need for excipients. By reducing the need for additional excipients, the coated particles can be used to create dosage forms with high drug loading.

Described herein is a composition comprising individual particles comprising an API-containing core (e.g., a core consisting of an API or an API and one or more excipients) enclosed by an silicon oxide layer, wherein the core has a median particle size, on a volume average basis, between <NUM> and <NUM>, and the silicon oxide layer has an average thickness of <NUM> to <NUM>.

In various embodiments, the temperature of the interior of the reactor does not exceed <NUM>, <NUM>, <NUM>; is <NUM> - <NUM>; or is <NUM> - <NUM> or is <NUM> - <NUM>.

Described herein is a method of preparing coated particles comprising an active pharmaceutical ingredient (API)-containing core enclosed by one or more silicon oxide layers, the method comprising:.

In various embodiments: step (a6) is not performed; step (a6) is performed; steps (a2) - (a6) are performed two or more times to increase the total thickness of the silicon oxide layer; the reactor contents are agitated prior to and/or during one or more of steps (a2) to (a6); the reactor pressure is allowed to stabilize following step (a1), step (a2), and/or step (a4); the reactor contents are agitated prior to and/or during step (a1), step (a3), and/or step (a5); a subset (e.g., some, but not all) of vapor or gaseous content is pumped out prior to step (a3) and/or step (a5); the silicon oxide layer has a thickness in a range of <NUM> to <NUM>; steps (a2) - (a6) are repeated two or more times and the core particles are not removed from the reactor between each repetition; steps (a2) - (a6) are repeated two or more times and the core particles are not removed from the reactor during step until the silicon oxide layer is complete; the core particles comprising an API further comprise one or more pharmaceutically acceptable excipients; the core particles consist of API; the core particles comprising an API have a median particle size, on a volume average basis between <NUM> and <NUM> prior to step (a1); the core particles have a median particle size, on a volume average basis between <NUM> and <NUM> prior to step (a1); the core particles have a median particle size, on a volume average basis between <NUM> and <NUM> prior to step (a1); the core particles comprise a first API and a second API; the core particles consist of an API; the core particles consist of a first API and a second API; the core particles comprise an API and one or more pharmaceutically acceptable excipients; the core particles comprise a first API, a second API and one or more pharmaceutically acceptable excipients; the particles remain in the reactor until the coating is complete; the core particles consist of an API and one or more pharmaceutically acceptable excipients; and core particles consist of a first API, a second API and one or more pharmaceutically acceptable excipients.

Moreover, one or more of the gases (e.g., water vapor and/or gaseous SiCl<NUM> and/or the inert gas) can be supplied in pulses in which the chamber is filled with the gas to a specified pressure, a holding time is permitted to pass (e.g., as short as <NUM> sec or as long as, e.g., one hour), and the chamber is evacuated to some extent by the vacuum pump before the next pulse commences. Thus, each of steps (a2), (a3), (a4) and (a6) can comprises multiple pulses.

In various embodiments: step (a1) further comprises one or both of loading particles comprising a second API into the reactor (second core particles) and loading particles comprising one more excipients into the reactor (excipient particles); the method further comprises admixing the coated particles comprising an API-containing core enclosed by one or more silicon oxide layers with a pharmaceutically acceptable diluent or carrier; and the method further comprises processing the coated particles comprising an API-containing core enclosed by one or more silicon oxide layers to form a tablet or capsule; and the method further comprises admixing the coated particles comprising an API-containing core enclosed by one or more silicon oxide layers with a pharmaceutically acceptable diluent or carrier to form a mixture and processing the mixture to form a table or capsule.

In some embodiments, the silicon oxide layer on the coated particles has a thickness in the range of <NUM> to <NUM>.

In some embodiments, the silicon oxide layer has a thickness in range of <NUM> to <NUM> or <NUM> to <NUM> or <NUM> to <NUM>.

The in some embodiments the API is suitable for oral administration.

In some embodiments, the API and/or the uncoated particles comprising an API do not comprise a metal oxide, do not comprise silicon oxide, and/or do not comprise aluminum oxide.

In some embodiments, the uncoated particles are at least <NUM>% wt/wt API. In some embodiments, the uncoated particles are at least <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>% wt/wt API. In some cases, the API is crystalline. In some embodiments, the coated particles have a D50 of <NUM> to <NUM> or <NUM> to <NUM> or <NUM> to <NUM> <NUM> to <NUM> on a volume average basis. In some embodiments, the coated particles have a D90 of <NUM> to <NUM> on a volume average basis. In some embodiments, the uncoated particles have a D50 of <NUM> to <NUM> or <NUM> to <NUM> or <NUM> to <NUM> <NUM> to <NUM> on a volume average basis. In some embodiments, the uncoated particles have a D90 of <NUM> to <NUM> on a volume average basis.

Methods and materials are described herein for use in the present invention; other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting.

There are various methods for providing a silicon oxide coating to an object by chemical vapor deposition or atomic layer deposition. Many of these processes require processing at an elevated temperature and/or the presence of a catalyst, for example, a Lewis base. Described herein is a method for applying a silicon oxide coating to particles comprising an API that does not entail the use of an elevated temperature or a catalyst. Instead, proper control of precursor (SiCl<NUM>) and oxidant (H<NUM>O) vapor pressure, hold time and the use of purging are used to create a conformal, pinhole coating.

The present disclosure provides methods of preparing pharmaceutical compositions comprising API (drug) containing particles encapsulated by one or more layers of silicon oxide. The coating layers are conformal and have a thickness of <NUM> - <NUM> nanometers. The particles to be coated can be composed of only APIs or a combination of APIs and one or more excipients. The coating process described herein can provide an API with an increased glass transition temperature for the API relative to an uncoated API, a decreased rate of crystallization for an amorphous form of the API relative to an uncoated API, and decreased surface mobility of API molecules in the particle compared to uncoated APIs. Importantly, API particle dissolution can be altered. Because the coating is relatively thin, drug products with high drug loading can be achieved.

The term "drug" in its broadest sense includes all small molecule (e.g., non-biologic) APIs. The drug could be selected from the group consisting of an analgesic, an anesthetic, an anti-inflammatory agent, an anthelmintic, an anti-arrhythmic agent, an antiasthma agent, an antibiotic, an anticancer agent, an anticoagulant, an antidepressant, an antidiabetic agent, an antiepileptic, an antihistamine, an antitussive, an antihypertensive agent, an antimuscarinic agent, an antimycobacterial agent, an antineoplastic agent, an antioxidant agent, an antipyretic, an immunosuppressant, an immunostimulant, an antithyroid agent, an antiviral agent, an anxiolytic sedative, a hypnotic, a neuroleptic, an astringent, a bacteriostatic agent, a beta-adrenoceptor blocking agent, a blood product, a blood substitute, a bronchodilator, a buffering agent, a cardiac inotropic agent, a chemotherapeutic, a contrast media, a corticosteroid, a cough suppressant, an expectorant, a mucolytic, a diuretic, a dopaminergic, an antiparkinsonian agent, a free radical scavenging agent, a growth factor, a haemostatic, an immunological agent, a lipid regulating agent, a muscle relaxant, a parasympathomimetic, a parathyroid calcitonin, a biphosphonate, a prostaglandin, a radio-pharmaceutical, a hormone, a sex hormone, an anti-allergic agent, an appetite stimulant, an anoretic, a steroid, a sympathomimetic, a thyroid agent, a vaccine, a vasodilator and a xanthine.

Exemplary types of small molecule drugs include, but are not limited to, acetaminophen, clarithromycin, azithromycin, ibuprofen, metaformin, theophylline, fluticasone propionate, salmeterol, pazopanib HCl, palbociclib, and amoxicillin potassium clavulanate.

Atomic layer deposition (ALD) (alternatively referred to as atomic layer coating (ALC)) is a thin film deposition technique in which the sequential addition of self-limiting monolayers of an element or compound allows deposition of a film with thickness and uniformity controlled to the level of an atomic or molecular monolayer. Self-limited means that only a single atomic layer is formed at a time, and a subsequent process step is required to regenerate the surface and allow further deposition.

Chemical vapor deposition (CVD), like ALD, is deposition technique that uses a gaseous precursor and a gaseous oxidant. However, the process is more continuous than ALD because the precursor and the oxidant can be present at the same time.

The term "reactor system" in its broadest sense includes all systems that could be used to perform ALD or mixed ALD/CVD or CVD. An exemplary reactor system is illustrated in <FIG> and further described below in the context of an ALD reaction. The same or a similar reactor system can be used to perform MLD, hybrid MLD/ALD.

<FIG> illustrates a reactor system <NUM> for performing coating of particles, with thin-film coatings. The reactor system <NUM> can perform the coating using ALD and/or hybrid, and/or MLD coating conditions. The reactor system <NUM> permits a coating process (ALD or MLD or hybrid), to be performed at a higher (above <NUM>, e.g., <NUM>-<NUM>) or lower processing temperature, e.g., below <NUM>, e.g., at or below <NUM>. For example, the reactor system <NUM> can form thin-film silicon oxides on the particles. In general, the particles can remain or be maintained within a desired temperature range. This can be achieved by having the reactant gases and/or the interior surfaces of the reactor chamber (e.g., the chamber <NUM> and drum <NUM> discussed below) remain or be maintained at such temperatures.

As an example, the reactor system <NUM> includes a stationary vacuum chamber <NUM> which is coupled to a vacuum pump <NUM> by vacuum tubing <NUM>. The vacuum pump <NUM> can be an industrial vacuum pump sufficient to establish pressures less than <NUM> Torr, e.g., <NUM> to <NUM> mTorr, e.g., <NUM> mTorr. The vacuum pump <NUM> permits the chamber <NUM> to be maintained at a desired pressure, and permits removal of reaction byproducts and unreacted process gases.

In operation, the reactor <NUM> performs the thin-film coating process by introducing gaseous precursors of the coating into the chamber <NUM>. The gaseous precursors are spiked alternatively into the reactor. This permits the process to be a solvent-free process. The halfreactions of the process are self-limiting, surface reactions, which can provide Angstrom level control of deposition. In addition, the reaction can be performed at low temperature conditions, such as below <NUM>, e.g., below <NUM>.

The chamber <NUM> is also coupled to a chemical delivery system <NUM>. The chemical delivery system <NUM> includes three or more gas sources 32a, 32b, 32c coupled by respective delivery tubes 34a, 34b, 34c and controllable valves 36a, 36b, 36c to the vacuum chamber <NUM>. The chemical delivery system <NUM> can include a combination of restrictors, gas flow controllers, pressure transducers, and ultrasonic flow meters to provide a controllable flow rate of the various gasses into the chamber <NUM>. The chemical delivery system <NUM> can also include one or more temperature control components, e.g., a heat exchanger, resistive heater, heat lamp, etc., to heat or cool the various gasses before they flow into the chamber <NUM>. Although <FIG> illustrates separate gas lines extending in parallel to the chamber for each gas source, two or more of the gas lines could be joined, e.g., by one or more three-way valves, before the combined line reaches the chamber <NUM>. In addition, although <FIG> illustrates three gas sources, the use of four gas sources could enable the in-situ formation of laminate structures having alternating layers of two different metal oxides.

Two of the gas sources provide two chemically different gaseous reactants for the coating process to the chamber <NUM>. For example, the first gas source 32a can provide gaseous silicon tetrachloride (SiCl<NUM>), whereas the second gas source 32b can provide water vapor.

One of the gas sources can provide a purge gas. In particular, the third gas source can provide a gas that is chemically inert to the reactants, the coating, and the particles being processed. For example, the purge gas can be N<NUM>, or a noble gas, such as argon.

A rotatable coating drum <NUM> is held inside the chamber <NUM>. The drum <NUM> can be connected by a drive shaft <NUM> that extends through a sealed port in a side wall of the chamber <NUM> to a motor <NUM>. The motor <NUM> can rotate the drum at speeds of <NUM> to <NUM> rpm. Alternatively, the drum can be directly connected to a vacuum source through a rotary union.

The particles to be coated, shown as a particle bed <NUM>, are placed in an interior volume <NUM> of the drum <NUM>. The drum <NUM> and chamber <NUM> can include sealable ports (not illustrated) to permit the particles to be placed into and removed from the drum <NUM>.

The body of the drum <NUM> is provided by one or more of a porous material, a solid metal, and a perforated metal. The pores through the cylindrical side walls of the drum <NUM> can have a dimension of <NUM> or less.

In operation, one of the gasses flows into chamber <NUM> from the chemical delivery system <NUM> as the drum <NUM> rotates. A combination of pores (<NUM>-<NUM>), holes (<NUM>-<NUM>), or large openings in the coating drum serves to confine the particles in the coating drum while allowing rapid delivery of precursor chemistry and pumping of byproducts or unreacted species. Due to the pores in the drum <NUM>, the gas can flow between the exterior of the drum <NUM>, i.e., the reactor chamber <NUM>, and the interior of the drum <NUM>. In addition, rotation of the drum <NUM> agitates the particles to keep them separate, ensuring a large surface area of the particles remains exposed. This permits fast, uniform interaction of the particle surface with the process gas.

In some implementations, one or more temperature control components are integrated into the drum <NUM> to permit control of the temperature of the drum <NUM>. For example, resistive heater, a thermoelectric cooler, or other components can be integrated in or on the side walls of the drum <NUM>.

The reactor system <NUM> also includes a controller <NUM> coupled to the various controllable components, e.g., vacuum pump <NUM>, gas distribution system <NUM>, motor <NUM>, a temperature control system, etc., to control operation of the reactor system <NUM>. The controller <NUM> can also be coupled to various sensors, e.g., pressure sensors, flow meters, etc., to provide closed loop control of the pressure of the gasses in the chamber <NUM>.

In general, the controller <NUM> can operate the reactor system <NUM> in accord with a "recipe. " The recipe specifies an operating value for each controllable element as a function of time. For example, the recipe can specify the times during which the vacuum pump <NUM> is to operate, the times of and flow rate for each gas source 32a, 32b, 32c, the rotation rate of the motor <NUM>, etc. The controller <NUM> can receive the recipe as computer-readable data (e.g., that is stored on a non-transitory computer readable medium).

The controller <NUM> and other computing devices part of systems described herein can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware. For example, the controller can include a processor to execute a computer program as stored in a computer program product, e.g., in a non-transitory machine readable storage medium. Such a computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. In some implementations, the controller <NUM> is a general purpose programmable computer. In some implementations, the controller can be implemented using special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

The operation is illustrated with a process for providing a silicon oxide coating, but the operation is similar for ALD, MLD, or hybrid method. Initially, particles are loaded into the drum <NUM> in the reactor system <NUM>. The particles can be an API, a solid dispersion of an API and one or more excipients, a mixture of two or more APIs or a mixture of one or more APIs or a mixture of one or more excipients. Once any access ports are sealed, the controller <NUM> operates the reactor system <NUM> according to the following recipe in order to form the thin-film oxide layers on the particles.

In a first reactant half-cycle, while the motor <NUM> rotates the drum <NUM> is to agitate the particles <NUM>:.

These steps (i)-(iii) can be repeated a number of times set by the recipe, e.g., two to ten times, e.g., six times.

Next, in a first purge cycle, while the motor <NUM> rotates the drum <NUM> to agitate the particles <NUM>:.

These steps (iv)-(vi) can be repeated a number of times set by the recipe, e.g., six to twenty times, e.g., sixteen times.

In a second reactant half-cycle, while the motor <NUM> rotates the drum <NUM> agitates the particles <NUM> as follows:.

These steps (vii)-(ix) can be repeated a number of times set by the recipe, e.g., two to ten times, e.g., six times.

Next, in a second (optional) purge cycle, while the motor <NUM> rotates the drum <NUM> is to agitate the particles <NUM> as follows:.

These optional steps (x)-(xii) can be repeated a number of times set by the recipe, e.g., six to twenty times, e.g., sixteen times.

This second purge cycle can be identical to the first purge cycle, or can have a different number of repetitions of the steps (x)-(xii) and/or different delay time and/or different pressure. The cycle of the first reactant half-cycle, first purge cycle, second reactant half cycle and second purge cycle can be repeated a number of times set by the recipe, e.g., <NUM> to <NUM> times.

As noted above, the inert gas purge after the second (water) half cycle is optional. It is been discovered that, for hydrophobic particles, e.g., hydrophobic APIs, it is not desirable to include an inert gas purge after the water half-cycle. Instead, the chamber can be pumped down to a pressure below <NUM> Torr, e.g., to between <NUM> Torr to <NUM> Torr, or to <NUM> Torr. In this way some residual water vapor remains in the chamber. The SiCl<NUM> is then flowed in to initiate the first reactant half-cycle and the residual moisture in the chamber allows the reaction to initiate on the API surface and proceed at a lower temperature. This process can be repeated <NUM> to <NUM> times, <NUM> to <NUM> times, to create a desired coverage of coating. Then the process can resume the normal purging process to reach the target coating thickness. Thus, in some cases, the inert purge gas is not used after the first or first and second water half cycle, but is used after subsequent water half cycles.

As noted above, the coating process can be performed at a low processing temperature, e.g., below <NUM> or below <NUM>, e.g., between <NUM> and <NUM> or between <NUM> and <NUM>. In particular, the particles can remain or be maintained at such temperatures during all of the steps (i)-(ix) noted above. In general, the temperature of the interior of the reactor chamber does not exceed <NUM> during the steps (i)-(xii). This can be achieved by having the first reactant gas, second reactant gas and inert gas be injected into the chamber <NUM> at such temperatures during the respective cycles. In addition, physical components of the chamber <NUM> can remain or be maintained at such temperatures, e.g., using a cooling system, e.g., a thermoelectric cooler, if necessary.

Provided are two exemplary methods for a pharmaceutical composition comprising a drug-containing core enclosed by one or more metal oxide materials. The first exemplary method includes the sequential steps of: (a) loading the particles comprising the drug into a reactor, (b) applying a vaporous or gaseous SiCl<NUM> to the substrate in the reactor, (c) performing one or more pump-purge cycles of the reactor using inert gas, (d) applying a vaporous or gaseous H<NUM>O to the substrate in the reactor, and (e) performing one or more pump-purge cycles of the reactor using inert gas. In some embodiments of the first exemplary method, the sequential steps (b)-(e) are optionally repeated one or more times to increase the total thickness of the one or more silicon oxide materials that enclose the solid core of the coated particles. In some embodiments, the reactor pressure is allowed to stabilize following step (a), step (b), and/or step (d). In some embodiments, the reactor contents are agitated prior to and/or during step (b), step (c), and/or step (e). In some embodiments, the reactor contents are agitated throughout the coating process. In some embodiments, a subset of vapor or gaseous content is pumped out prior to step (c) and/or step (e).

The second exemplary method includes (e.g., consists of) the sequential steps of (a) loading the particles comprising the drug into a reactor, (b) reducing the reactor pressure to less than <NUM> mTorr, (c) pressurizing the reactor by adding vaporous or gaseous SiCl<NUM>, (d) allowing the reactor pressure to stabilize, (e) agitating the reactor contents, (f) pumping out a subset of vapor or gaseous content and determining when to stop pumping based on analysis of content in the reactor including precursor and byproduct of precursor reacting with exposed hydroxyl residues on substrate or on particle surface, (g) performing a sequence of pump-purge cycles of the reactor using insert gas, (h) pressuring the reactor by adding a vaporous or gaseous H<NUM>O, (j) allowing the reactor pressure to stabilize, (k) agitating the reactor contents, (l) pumping out a subset of vapor or gaseous content and determining when to stop pumping based on analysis of content in reactor including precursor, byproduct of precursor reacting with exposed hydroxyl residues on substrate or on particle surface, and unreacted oxidant, and optionally, (m) performing a sequence of pump-purge cycles of the reactor using insert gas. In some embodiments of the second exemplary method, the sequential steps (b)-(m) are optionally repeated one or more times to increase the total thickness of the one or more metal oxide materials that enclose the solid core of the coated particles.

Pharmaceutically acceptable excipients include, but are not limited to:.

In this Example, one of the methods disclosed for preparing silicon oxide coated particles comprising an API was performed and the data is presented. The vaporous or gaseous precursor is SiCl<NUM>, the byproduct gaseous HCl formed after SiCl<NUM> reacts with exposed hydroxyl groups on the particles or on surface of the coated particles, and the oxidant is H<NUM>O.

In brief, the method comprised the sequential steps of:.

Additionally, the steps of (b)-(i) were repeated more than once to increase the total thickness of the silicon oxide that encloses the drug particle core.

Three different APIs were coated with silicon oxide. Table <NUM> summarizes the reaction conditions and results. Acetaminophen (APAP) and theophylline (THEO) are hydrophilic (LogP <NUM> and -<NUM>, respectively). Flowability (Flow Function; "FF") of the uncoated APAP particles was <NUM>. Flowability of the uncoated THEO particles was <NUM>. As can be seen in Table <NUM>, for these APIs better results were achieved with a N<NUM> purge after the water cycle. Without being bound by any theory, it may be that in the absence of a purge, residual water vapor causes deposition that is too rapid to yield improved flowability. In addition, poor flowability might be caused by excess moisture in coated powder. In contrast, ibuprofen (uncoated FF <NUM>), which is hydrophobic (LogP <NUM>), better results were achieved with a higher SiCl<NUM> pressure and no N<NUM> purge (<NUM> mTorr H<NUM>O at end of each H<NUM>O).

<FIG> is a series of images of theophylline particles. The panels at the left are TEM cross sections of particles coated with silicon oxide as described above. The center panels are SEM images of the uncoated particles, and the panels at the right are SEM images of the coated particles.

<FIG> is a series of images of acetaminophen particles. The panels at the left are TEM cross sections of particles coated with silicon oxide as described above. The panels at the right are SEM images of the coated particles.

<FIG> is a series of images of TiO<NUM> particles coated with silicon oxide as described above.

Claim 1:
A method of preparing coated particles comprising an active pharmaceutical ingredient (API)-containing core enclosed by one or more silicon oxide layers, the method comprising:
(a1) loading core particles comprising an API into a reactor;
(a2) applying gaseous SiCl<NUM> to the core particles in the reactor;
(a3) performing one or more pump-purge cycles of the reactor using inert gas;
(a4) applying gaseous H<NUM>O to the core particles in the reactor;
(a5) lowering the gaseous H<NUM>O in the reactor to below <NUM> Torr; and
wherein steps (a2)-(a5) take place between <NUM> and <NUM> and in the absence of a catalyst.