SOLID SUPPORT MEDIATED METHOD FOR THE SYNTHESIS
OF KETONE OXIME LINKERS AND METHOD OF PRODUCING
LIBRARIES OF KETONES THEREFROM
The present invention relates to a solid support mediated method for the synthesis of ketone oxime linkers, intermediate compounds, a library of ketones, a method for synthesizing a library of diverse ketones, and an assay kit for identifying ketones having biological or other activity.
Small-molecule ketones of the following structure have been shown to have biological activity:
Formula (V) where each of R8 or R9 is independently selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, and heteroaryl, and R8 and R9 are either independent or together form a ring.
For example, there are several ketone-containing drugs in various stages of efficacy evaluation. A sampling of these ketone-containing drugs is shown below:
There are known methods for synthesizing useful ketones on a solid support. For example, ketones have been reacted with resin-bound amines to form imines. See Worster, P.M.; McArthur, C.R.; Lenznoff, C.C. Agnew. Chem. Int. Ed. Engl. 1979, 19, 221. However, this approach suffers from the drawback of extreme hydrolytic sensitivity.
In a related approach, a semicarbazide linker can immobilize aldehydes and ketones on a solid support during the synthesis of oligopeptides. See Murphy, A.M.; Dagnino, R.; Vallar, P.L.; Trippe, A.J.; Sherman, S.L.; Lumpkin, R.H.; Tamura, S.Y.; Webb, T.R. J. Am. Chem. Soc 1992, 114, 3156. See also Poupart, M.; Fazal, G.; Goulet, S.; Mar, L.T. J. Org. Chem. 1999, 64, 1356. This semicarazide linker is also stable to palladium-mediated Suzuki coupling conditions. See Giroux, A.; Han, Y. Book of Abstracts 1999, 217th ACS National Meeting, Anaheim, Calif.
Ketal linking strategies have also been attempted, but have achieved only limited success. One aspect of this invention is method of synthesizing a compound, comprising: reacting a compound of the formula (I)
wherein each of R
1, R
2, and R
4 is a stable moiety independently selected from the group consisting of halo, haloalkyl, cyano, nitro, R
a-Q-, R
a-Q-alkyl, R
a-Q-alkenyl, R
a-Q-alkynyl, R
a-Q-arylalkyl and R
a-Q-aryl;
Ra is H, alkyl, aryl, or arylalkyl;
Q is a single bond, -O-, -NRb-, -CO-, -NRb-CO-, -CO-NRb-, -CO-O-, -O-CO-, -S(0)r> -S(O)rNRb-, -NRb-S(O)r; i is O, 1 or 2; j is 1 or 2; Rb is H, alkyl, aryl or arylalkyl, wherein Ra and Rb, optionally, together with the nitrogen to which they are attached form a ring;
R3 is -Rc-X-;
X is O or S; Rc is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl;
R5 is halo, nitro, or haloalkyl; and
R6 is cyano or a group of the formula (II)
L is O, S, or NH; and
R7 is alkyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl;
is solid support;
with a compound of the formula (III)
R8 is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl;
R _9 : is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl, wherein R8 and R9 are either independent or together form a ring;
R )1I3J is -NH-, -O-, or -S-;
to form a compound of the formula (IV)
wherein n is an integer > 0 and R
1"4, R
6, and R
8"9 and R
13 are as defined
above.
Compound (IV) is an intermediate. This intermediate can be chemically derivatized before cyclization and displacement to replace groups R8 and/or R9 with R8 and/or R9'. The intermediate compound (IV) is preferably stable to a wide range of chemical conditions.
When the intermediate compound (IV) is cyclized, the cyclized heterocycle remains bound to the solid support, and a ketone of the formula (V) is released:
wherein R
8 and R
9 are as defined above.
A third aspect of the invention is directed to a library of ketones. This library comprises a plurality of diverse compounds of the formula (V)
where R
8 and R
9 are as defined above.
A fourth aspect of the invention is directed to a method for the synthesis of a library of diverse ketones. A fifth aspect of the invention is directed to an assay kit for the identification of compounds having biological or other activity, this kit comprising assay materials and well plate apparatus where each well in this apparatus comprises a compound of the library described above.
This invention relates to an improved method for synthesizing useful ketones. The method for generating a library of ketones disclosed herein involves a cyclorelease reaction. "Cyclorelease" or "cyclization and release" describe a reaction that forms a cyclized system with a simultaneous release of a product from a solid support. The phrase "cyclization and displacement of product from a solid support" refers to the same reaction. In this case, the cyclized system remains attached to the solid support, and a ketone is released from the solid support.
This reaction can be fine-tuned based on the electronic nature of a benzonitrile ring involved in the cyclorelease reaction. Basically, a desired sensitivity to aqueous acidic conditions can be achieved by using differently-substituted benzonitrile rings. Advantageously, the synthesis of the present invention involves combinatorial chemistry. Combinatorial chemistry allows researchers to make collections, or libraries,
of compounds by parallel synthesis of large numbers of derivatives of selected classes
of organic compounds which can be screened for biological and other activities. By
screening these compounds against key receptors or enzymes, useful structure-function
data can be obtained, speeding the search for new therapeutic agents. A solid support
mediated method for the synthesis of ketones and the use of this solid support mediated
method for the synthesis of a library of diverse ketones is desirable.
Definition of terms
"Solid support" has a broad meaning including but not limited to a resin, a
polymer, a gel, glass beads, silica gel, a ceramic solid support or other solid
composition. One preferred solid support is a derivative of Merrifield's resin.
"Oxime" is a compound of the following formula:
.HR 13
N
R9 R8 where R8 and R9 and R13 are defined as above.
"Solid support bound oxime" is a solid support that has at least has one oxime
moiety. For example, the following compound satisfies this definition.
In this formula, " is solid support and all the substituent groups are as defined above.
"Solid support bound member" is a solid support that has at least one functional moiety chemically attached thereto. For example, the following compound meets this definition:
"Oxime resin" is a solid support wherein the functional moiety is an oxime, and the solid support is a resin. "Kaiser resin" is an oxime functionalized polystyrene resin, an example of which is defined by E.T.Kaiser in a 1980 publication (Degrado, W.F.;Kaiser. E.T.; J.Org. Chem. ,1980, 45, 1295). A preferred resin is an oxime functionalized polystyrene, such
as an oxime-polystyrene resin derived from p-nitrobenzophenone polystyrene resin according to the following formula.
"Merrifield's resin" is a resin according to the following formula:
"Halo" is a member selected from the group consisting of fluoro, chloro, bromo and iodo.
"Alkyl" is the radical of saturated aliphatic groups, including straight-chain alkyl groups, branched-chain alkyl groups, cycloalkyl groups, alkyl substituted cycloalkyl groups, and cycloalkyl substituted alkyl group, and which groups may include one or more double or triple bonds. In preferred embodiments, a straight chain or branched chain alkyl has 30 or fewer carbon atoms in its backbone, and more preferably 20 or fewer and most preferred 10 or fewer. Likewise, preferred cycloalkyls have from 3-10 carbon atoms in their ring structure, and more preferably have 3-6 carbons in the ring structure. Particularly preferred alkyl substituents include methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, iso-butyl, tert-butyl, sec-butyl, cyclobutyl, pentyl, hexyl, cyclohexyl, etc. Unless the number of carbons is otherwise specified, "lower alkyl" as used herein means an alkyl group, as defined above, but having from one to ten
carbons, more preferably from one to six carbon atoms in its backbone structure. The aliphatic cyclic groups can be single or polycyclic containing between about 1 to 12 carbons per ring, but preferably between 1 and 9 carbons per ring.
"Haloalkyl" and "alkylhalo" both refer to mono or poly halogen radical substituted alkyl radicals, with the alkyl radicals having the analogous length and possible substitution as described above.
"Hydroxyalkyl" and "alkylhydroxide" and "alkyl alcohol" all refer to a mono or poly hydroxide radical substituted alkyl radical, with the alkyl radicals having the analogous length and possible substitution as described above. "Alkyloxyalkyl ether" and "alkyloxyaryl ether" both refer to ether functional radicals of either the dialkyl radical or the alkyl, aryl radical configuration, with the alkyl radicals and the aryl radicals having the analogous length and possible substitution to the alkyl and aryl radicals defined herein.
"Alkenyl" and "alkynyl" refer to unsaturated aliphatic substituents analogous in length and possible substitution to the alkyl radicals described above, but which contain at least one double or triple bond, respectively.
"Amino" means an amino radical substituted with up to 2 alkyl radicals as defined above or with 1 alkyl radical and a hydrogen radical, or with two or more hydrogen radicals or with the substitution required to complete the nitrogen's valence requirements.
"Aryl" as used herein includes 5-10 membered aromatic monocyclic or fused polycyclic moieties which may include from zero to four heteroatoms selected from the
group consisting of oxygen, sulfur and nitrogen, for example, benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine, pyrimidine, naphthyline, benzathiazoline, benzothiapene, benzofurans, indole, quinoline, etc. The aryl group can be substituted at one or more positions with halo, alkyl, alkoxy, alkoxy carbonyl, haloalkyl, cyano, amino sulfonyl, aryl, sulfonyl, aminocarbonyl, carboxy, acylamino, alkyl sulfonyl, amino and substituted or unsubstituted substituents.
"Heteroaryl" is a mono-, bi- or tricyclic, -N-, -O- or -S- heteroaryl substituent, such as benzofuran, benzothiophene, furan, imidazole, indole, isothiazole, oxazole, piperazine, pyrazine, pyrazole, pyridazine, pyridine, pyrimidine, pyrrole, quinoline, thiazole and thiophene.
"Library" means a large number of chemical derivatives used in screening for biological activity or other activity. In general a library will have greater than 20 members, preferably the library will have at least 50 members, more preferably the library will have at least 96 members and most preferably the library will have at least 1000 members.
"Chemically derivatized" means the chemical manipulation such as addition to, oxidation of, substitution for, reduction of, or cyclization of the selected R group or R groups of the intermediate. Chemical derivatization also means the manipulation of two or more groups of the intermediate such that additional aryl or alkyl rings are formed and which rings may be fused or unfused to the intermediate ring, and which new ring may be substituted with further chemically derivatizable substituents.
"Pharmaceutically acceptable salt" and "salts thereof means organic or inorganic salts of the pharmaceutically important molecule. A pharmaceutically acceptable salt may involve the inclusion of another molecule such as an acetate ion, a succinate ion or other counterion. The counterion may be any organic or inorganic moiety that stabilizes the charge on the parent compound. Furthermore, a pharmaceutically important organic molecule may have more than one charged atom in its structure. Situations where multiple charged atoms are part of the molecule may have multiple counterions. Hence, the molecule of a pharmaceutically acceptable salt may contain one or more than one charged atoms and may also contain, one or more than one counterion. The desired charge distribution is determined according to methods of drug administration. Examples of pharmaceutically acceptable salts are well known in the art but, without limiting the scope of the present invention, exemplary presentations are in the Physician's Desk Reference, The Merck Index, The Pharmacopoeia and Goodman & Gilman's The Pharmacological Basis of Therapeutics. "TFA" means trifluoro acetic acid, "HCI" means hydrochloric acid, "THF" means tetrahydrofuran, "DMF" means dimethylformamide, "DIPEA" means diisopropylethyl amine, "TMS" means a trimethyl silyl radical and "TBS" means a .-butyldimethyl silyl radical.
"Leaving group" means halo, oxo, thioxo radicals and activated alcohols such as a p-toluene sulfonyl activated alcohols and other groups that are susceptible to displacement and replacement by a nucieophile under selected conditions of temperature, solvent and time.
"Scaffold" means a common chemical structure found within a library of organic compounds. Similarly, within a combinatorial chemical library the scaffold forms the basis for a diverse series of chemical derivatization, additions and subtractions. Importantly, regardless of the extent of the chemical derivatization performed on the scaffold, the product is within the scope of the combinatorial library.
All other acronyms and abbreviations have the corresponding meaning as published in journals relative to the art of organic chemistry.
A general method for making compounds according to the invention includes the following method: reacting a compound of the formula (I)
wherein each of R
1, R
2, and R
4 is a stable moiety independently selected from the group consisting of halo, haloalkyl, cyano, nitro, R
a-Q-, R
a-Q-alkyl, R
a-Q-alkenyl, R
a-Q-alkynyl, R
a-Q-arylalkyl and R
a-Q-aryl;
Ra is H, alkyl, aryl, or arylalkyl;
Q is a single bond, -O-, -NRb-, -CO-, -NRb-CO-, -CO-NR -, -CO-O-,
-O-CO-, -S(O),-, -S(O)rNRb-, -NRb-S(O)r; i is 0, 1 or 2;
j is 1 or 2;
Rb is H, alkyl, aryl or arylalkyl, wherein Ra and Rb, optionally, together with the nitrogen to which they are attached form a ring;
R3 is -Rc-X-;
X is O or S;
Rc is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl;
R _5 : is halo, nitro, or haloalkyl; and
R _6 ; is- cyano or a group of the formula (II)
L is O, S, or NH; and
R7 is alkyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl;
is solid support;
with a compound of the formula (III)
R
18 is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl;
R9 is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl, wherein R8 and R9 are either independent or together form a ring;
R ,1'3J is -NH-, -O-, or -S-
to form a compound of the formula (IV)
wherein n is an integer > 0 and R 1-4 ,
D R6 , and 1
D R8-9 and D R13 a, re as defined above
The compound of formula (I) is prepared by reacting commercially-available Merrifield's resin with a fluorobenzonitrile derivative in the presence of a solvent (such
as DMF) for a sufficient amount of time for the reaction to complete. The electronic nature of this ring affects the sensitivity of the intermediate compound (IV) to acidic conditions, which in turn affects the conditions under which the intermediate compound (IV) cyclizes and releases a ketone product. Although many fluorobenzonitrile derivatives are within the scope of this invention, the most preferred fluorobenzonitrile has this structure:
When the most preferred flourobenzonitrile is reacted with Merrifield's resin, the following resin is synthesized:
The above-illustrated resin is a preferred resin. Any polymer resin is a preferred solid support. Alternative solid supports include a gel, glass beads, silica gel, and a ceramic solid support.
The oximes of the formula (III) can generally be prepared through reactions similar to this type of reaction:
Standard substitutions in solvents, substituents, and other reaction conditions such as temperature and pH are within the scope of this invention.
Preferably, at least one of R8 and R9 are alkyl or aryl. More preferably, at least one of R8 and R9 is substituted aryl. In another preferred embodiment, at least one of R8 and R9 is trifluoromethyl, pyridine, or thiazole. Preferably, one of R8 and R9 is lower alkyl, most preferably methyl. R13 is selected from the group consisting of -NH-, -O- and -S-, most preferably R13 is -O-.
During the above-described synthesis, an intermediate compound of formula (IV) is formed:
wherein n is an integer > 0 and R
1"4, R
6, and R
8"9 and R
13 are as defined above. This intermediate (IV) is optionally chemically derivatized at R
8"9 prior to the cyclization and displacement procedure to form a corresponding intermediate of the formula (IV)
wherein n is an integer > 0 and R
1"4, R
6, and R
13 are as defined above, and wherein either both R
8 and R
9 are different from R
8 and R
9 or only one of R
8 and R
9 is different from R
8 and R
9. Examples of chemical derivatization reactions include, but are not limited to, the following general derivatizations procedures:
Chemical reaction conditions suitable for BOC (t-butyloxycarbonyl) removal/acylation, TMS (trimethylsilyl) or other silicon based alcohol-protecting group removal (FVaqueous acid), Mitsunobu reaction (O. Mitsunobu, Synthesis 1981, 1-28), Suzuki coupling (N. Miyaura, A. Suzuki, Chem. Com/nun.1979, 866), Horner-Emmons type olefinations (W.S. Wadsworth, Jr., W.D. Emmons, J. Chem. Soc.83, 1733 (1961 )), reductive aminations (Klyeuv and Khidekel, Russ. Chem. Rev. 49, 14-27 (1980)) and ester hydrolysis/amidation reaction conditions.
If the compound (IV) has not been derivitized, when cyclization and displacement occur, a heterocyle remains bound to the solid support and a ketone is released according to formula (V).
If the compound (IV) has been derivitized into compound (IV), then when cyclization and displacement occur, a heterocyle remains bound to the solid support and a ketone is released according to formula (V).
The temperature for the cyclization and displacement procedure may be between about 0 and 85° C but is preferably between about 30 and 70° C and is most preferably between about 50 to 60 °C. The solvents suitable for the cyclization and displacement procedure include protic and aprotic solvent mixtures, aqueous and anhydrous solvent mixtures. A preferred solvent is TFA, a more preferred solvent mixture is TFA:H2O a most preferred solvent mixture is TFA:5 N HCI/H2O. Although a solvent mixture of TFA:5 N HCI/H2O is most preferred, the ratio of this TFA:5 N HCI/H2O mixture may vary between about 1 :1
to about 99:1 TFA:5 N HCI/H2O, but preferably is between about 80:1 to 1 :1 TFA:5 N HCI/H2O, and is most preferably at about 4:1 TFA:5 N HCI/H2O. The particular sensitivity to acidic conditions depends on the particular fluorobenzonitrile ring used. The time for the cyclization and displacement reaction may vary, but generally is between about 1 minute and 4 days but preferably between about 1 hour and 20 hours.
Using the methods disclosed herein, a library of diverse ketones of the formula (V) and (V) can be synthesized:
R8 is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl.
R is alkyl, alkenyl, alkynyl, aryl, arylalkyl, alkyloxyalkyl, aryloxyalkyl, alkylamino, dialkylamino, arylamino, alkoxycarbonyl, amino, alkoxy, hydroxy, or heteroaryl, wherein R8 and R9 are either independent or together form a ring.
Either both R8' and R9' are different from R8 and R9 or only one of R8' and R9' is different from R8 and R9. In a preferred embodiment, at least one of R8 and R9 (or R8 and R9 as the case may be) is trifluoromethyl, 2-pyridine-, or 2-thiazole. In another preferred embodiment one of R8 and R9 (or R8 and R9 as the case may be) is lower alkyl, most preferably methyl. In another preferred embodiment at least one of R8 and
R9 (or R8 and R9 as the case may be) is a substituted aryl, most preferably having only one substituent wherein the substituent is halo, alkoxy, nitro, or fe/f-butyl.
All of the compounds in such a library have a common scaffold — a ketone moiety. When preparing a library according to the present invention, diversity is introduced via the R8 and R9 substituents as discussed more fully above. These substituents are selected to allow the creation of a chemically diverse library that, as one goal, maximizes the exploration of molecular spatial properties. Such maximization increases the likelihood of creating compounds that will be biologically active against selected targets.
An assay kit is useful for identifying biologically active compounds in the library of diverse ketones produced by the methods disclosed herein. An assay kit comprises assay materials and a well plate apparatus wherein each well in the apparatus comprises a compound of the library described above.
The creation of a library of diverse compounds can be carried out by way of parallel synthesis in any reaction vessel capable of holding the liquid reaction medium and having, preferably, inlet and outlet means. For small-scale synthesis of multiple products, the solid support mediated method of the invention is preferably carried out in containers adaptable to parallel array syntheses. With parallel array synthesis, individual reaction products are prepared in
each of multiple reaction zones. The reaction zones are physically separated from one another in a reaction vessel. Compounds can be added to the reaction vessel by multiple delivery apparatus, automated or robotic apparatus, any of which may be either manually or computer controlled. A preferred parallel synthesis embodiment of the present invention is a diverse ketone compound library in the form of a plurality of wellplates, each wellplate having wells containing a separate reaction product (library compound). In such cases, their wellplate number and "x" column and "y" wellplate row coordinates conveniently identify the library compounds. The process of making the library of ketone compounds may be conveniently carried out in a conventional wellplate apparatus. It is particularly advantageous to carry out the method of the invention in a standard wellplate apparatus such as a plastic 96 well microtiter plate.
Typically, the wellplate apparatus is in the form of a rigid or semi-rigid plate, the plate having a common surface containing openings of a plurality of reservoirs arranged in rows and columns. A standard form of wellplate apparatus is a rectangular plastic plate having 8 rows and 12 columns (total 96) of liquid retaining depressions, or reservoirs, on its surface. A wellplate apparatus may optionally have other elements of structure such as a top or cover (for example, plastic or foil), a bottom in a form such as a plate or reservoir, clamping means to secure the wellplate and prevent loss of its contained compounds.
The library of ketones formed using the solid support mediated method aspects of the invention can be used to screen compounds for biological or other activity.
Myriad biological assays are known in the art and can be used to screen the library of diverse ketone compounds.
The libraries of diverse ketones can be screened for biological activity. Generally, the library to be screened is exposed to a biological substance, usually a protein such as a receptor, enzyme, membrane binding protein or antibody, and the presence or absence of an interaction between the heterocycle derivative and the biological substance is determined. Typically, this comprises determining whether the biological substance is bound to one or more of the members of the library. Such binding may be determined by attaching a label to the biological substance.
Commonly used labels include fluorescent labels. Other methods of labeling may be used, such as radioactive labels. The degree of binding affinity may be determined by quantitating the amount or intensity of the bound label. Thus, various biologically active compounds may be selected by identifying which compounds bind the particular biological substance most effectively.
Illustrative additional assays include, but are not intended to be limited to in vitro assays such as enzymatic inhibition, receptor - ligand binding, protein - protein interaction, andprotein - DNA interaction; cell based, functional assays such as transcriptional regulation, signal transduction / second messenger, and viral infectivity; add, incubate & read assays such as scintillation proximity assays (SPA), fluorescence polarization assay, fluorescence correlation spectroscopy, colorimetric biosensors,
cellular reporter assays using reporter genes such as luciferase, green fluorescent
protein, β-lactamase, and the like; and electrical cell impedance sensor assays.
All of the above assays are known in the art to be predictive of success for an associated disease state.
EXAMPLES
The following examples are provided as illustration only, and are not intended to limit this invention in any way.
Example A For Preparing A Resin
To Merrifield's resin (15 f, 1.013 mmol/g, 15.2 mmol) in a tared 250 mL vessel equipped with fritted glass filter was added DMF (120 mL), cesium carbonate (12.4 g, 37.9 mmol), sodium iodide (5.7 g, 37.9 mmol), and 2-fluoro-4-hydroxybenzonitrile (5.1 g, 37.9 mmol). The reaction vessel was rotated at 55 °C in a Robbins oven for 12 h, and allowed to cool for 10 min. The resin was then rinsed with 2 x 75 mL of H2O, 2 x 75 mL of MeOH, 2 x 75 mL of CH2CI2, 2 x 75 mL of MeOH, 2 x 75 mL of H2O, and 4 x 75 mL of MeOH. The resin was dried in a 35 °C in vacuum oven for 12 h. The increase in resin weight (1.36 g) corresponds to a loading yield of 91 %. Elemental analysis for fluorine gives a 99% loading yield, and for nitrogen, 83%. Elemental analysis confirms that no chlorine remains from the initial Merrifield's resin.
A variety of fluororesins can be prepared according to this general formula. Depending on the electronic nature of the particular fluorbenzonitrile ring used to synthesize a particular fluororesin, different conditions may be required for the
cyclization and release reaction. In certain cases, harsh acidic conditions may be required. In other cases, milder aqueous acid conditions may be sufficient.
Example B For Preparing A Resin
Kaiser's resin can be modified in according to the following reaction in preparation for a cyclorelease reaction.
In this reaction, X is a leaving group on the benzonitrile ring. The loading yield of the benzonitrile ring depends on both the leaving group and the solvent. The highest loading yields were achieved when X was F, NO2, or Cl. A detectable loading yield was also achieved when X was Br or I. Preferred solvents were THF, DMF, and DMSO. In the above reaction, the solvent contained included KOBu1. The reaction was allowed to complete for 12 h at 55 °C.
% loading yield x THF DMF DMSO
64 41 47
N02 72 41 54
Cl <5 <5 15
Br <5 - -
1 <5 - -
Steric effects affect the loading yield of the benzonitrile ring onto the resin as shown below.
This reaction was run in TMF containing KOBu1 for 12 h at 55 °C. The leaving group on the benzonitrile ring was F. The presence or absence of substituents of various sizes at the 3, 4, 5, and 6 position on the benzonitrile ring affected the loading yield of the benzonitrile ring onto the resin.
Substituent % loading yield
H at 3,4,5,6 64
H at 4,5,6, 83 CF3at 3
H at 3,5,6, 80 MeO at 4
H at 3,5,6, 90 Br at 4
H at 3,5,6, 83 CN at 4
H at 3,4,6, 95 NQ2at 5
H at 3,4,5, 69 CF3 at 6
This table shows that substitutions at the 4 and 5 position appear to increase the loading yield for steric reasons.
General Example For Loading An Oxime Onto A Synthesized Resin
In this general example, it is preferred that R8 and R9 are either aryl or alkyl. It is also preferred that R13 is O. However, these substituents can be any of the substituents defined above. Generally, an oxime that has been dissolved in an organic solvent is added to an arylflouride resin. The reaction vessel is rotated in heat for 2 to 6 h, preferably 3 to 5 h, then allowed to cool. The resin is then rinsed with organic solvents (such as CH2CI2) and inorganic solvents (such as H2O), then dried. A difference in the weight of the resin indicates the loading yield of a particular oxime onto an arylfluoride resin.
General Example Of On-Resin Synthesis
This illustration shows the derivitization from (IV) to (IV). A broad range of derivitization reactions are possible so long as the intermediate remains stable (does not cyclize). As mentioned above, such reactions include BOC removal/acylation, TMS or other silicon based alcohol-protecting group removal, Suzuki coupling, Horner- Emmons type olefinations, reductive aminations.and ester hydrolysis/amidation reactions.
General Example Of Cyclization and Release
Although not wanting to be bound by a theoretical explanation of a proposed chemical mechanism, the following equation is useful in explaining a cyclization and release reaction.
In short, the intermediate (IV) or (IV) is cyclized, forming a heterocyle that remains attached to a solid support. Simultaneously, a ketone is released. Depending on the electronic nature of the particular benzonitrile ring, different conditions may be required for the cyclization and release reaction. In certain cases, harsh acidic conditions may be required. In other cases, milder aqueous acid conditions may be sufficient.
Generally, the intermediate (IV) or (IV) is suspended in a TFA/H2O (about 4:1 by volume) solution or a TFA/HCL (using 5 N HCI) solution, depending upon the electronic nature of the benzonitrile ring. Desired levels of acidity may vary. The suspension is then rotated in heat (preferably 40 to 65 °C, more preferably 50 to 60°C) for from about 1 h to about 4h, preferably about 2 h. After cooling, the resin is then the TFA/H2O or the TFA/HCL solution is collected. Then the resin is washed in an organic solvent,
preferably CH2CI2. The washings are combined, collected, and concentrated in vacou to give the crude product ketone.
Specific Examples: Table 1
Five specific, non-limiting examples are included herein. Each of the examples used a different oxime of formula (III) to produce a different ketone of formula (V). However, each of the oximes were subjected to very similar reaction conditions. Each oxime was loaded onto the same arylfluoride resin:
in the same manner. In a vial, the oxime was dissolved in 2 mL DMSO, to which KOBu
1 (in THF) was added. This oxime solution was then added to the arylfluoride resin in a tared 25 mL vessel equipped with fritted glass filter. The reaction vessel was rotated at 55 °C in a Robbins oven for 4 h, and allowed to cool for 10 min. The resin was then rinsed with 2
x 5 mL of CH
2CI
2, 2
x 5 mL MeOH, 2
x 5 mL of H
2O, and 4
x 5 mL of MeOH. The resin was then dried in a 35 2
x 5 mL vacuum oven for 12 h. At this point, the loading yield was calculated by the difference in weight from the starting resin to the final resin.
Next, the resin was suspended in TFA (4 ml) and H
2O (1 mL) and rotated at 55 °C in a Robbins oven for 2h. After cooling for 10 min, the TFA/H
2O solution was collected and the resin was washed with 2
x 2 mL of CH
2CI
2. The washings were combined, collected, and concentrated in vacuo to give the crude product ketone. All crude yields were greater than 96 % based on HPLC analysis. Final yields of ketones were calculated based on the amount of oxime that loaded onto the resin. In each case, the NMR of the resultant was identical to that of the known ketone.
The results are displayed on Table 1.
Table 1
It should be understood that a wide range of changes and modifications can be made to the embodiments described above. It is therefore intended that the foregoing description illustrates rather than limits this invention, and that it is the claims, including all equivalents, which define this invention.