PHOSGENATED OXIME RESINS AND THEIR PREPARATION

Abstract: This invention relates to methods for preparing novel, solid-phase transfer reagents, specifically phosgenated oxime resins and non-symmetrical ureas, that are useful as supports in combinatorial synthesis for the creation of libraries of compounds for lead identification.

Description: TITLE PHOSGENATED OXIME RESINS AND THEIR PREPARATION FIELD OF INVENTION The present invention relates to a method ot preparation of a novel, solid-phase reagent that is useful in combinatorial synthesis for the creation of libraries of compounds for lead identification More specifically, the method produces phosgenated oxime resins. BACKGROUND The facile manipulation of reactive functionality is a key factor m the development of efficient, high-yielding methods tor combinatorial syntheses For example, activated carboxylic acid derivatives have served as reactive building blocks in the solid-phase preparation of a wide variety ot oligomeπc and small molecule libraries. In most cases, the solid-phase protocol allows reactions on a polvmer-bound scaffold to be driven to completion bv making use ot large excesses ot reagents in solution that can be easih tillered away from the polymer support After the scaffold has been modified, an additional cleavage step then frees the small molecule from the polvmcr support into solution for isolation An alternative approach is to support a reagent or catalyst that can be used in excess to induce a chemical transformation on other reagents in solution. and once again, simple filtration can serve as a means tor product separation and isolation Isocyanates are well known in the ai t to be usetul intermediates in the production of pharmaceuticals and agrochemicals \ ι\ pιr_al preparation of isocyanates involves the phosgenation oi pπman amines Phosgene is a very reactive reagent, and many compounds hav e runcuonal groups in addition to the primary amine which would also be react w uh phosgene Therefore, mam highly functionalized compounds cannot be prepared irom the amine as the starting point via the isocyanate as an intermediate Similarly, unsymmetπcal ureas with different groups on each of the nitrogen atoms adjacent to the carbonyl. are also difficult to directly synthesize u ithout the use of laboriously prepared protecting groups A need exists to develop simple syntheses to overcome these problems The reaction of oximes with phosgene in solution phase to produce oxime-deπved c loroformates is known in the art Itoh et al (Organic Syntheses. 59. 1975. 95-101 and Bull of the Chem SOL of Japan. 50 . 1977. 718-721) have used the reaction ot various oximes with phosgene as part of a scheme to prepare a t-butoxycarbonvlatmg reagent, which is used in peptide synthesis The chloroformate that is formed is in the solution phase and is never isolated, but rather is used in situ The use ot the chloroformates in syntheses has the disadvantage that it must be stored and used under an men atmosphere since they are very reactive and decompose in open air liberating HCl DeGrado and Kaiser (J Org Chem 1980, 45. 1295-1300 and J Org Chem. 1982, 47, 3258-3261) have used an oxime resin as a solid phase reagent for peptide synthesis. A C-terminal ammo acid is anchored onto the oxune resin as its oxime-deπved ester, allowing further amino acids to be added stepwise by standard peptide coupling Once the desired peptide is assembled , it is cleaved from the oxime resin by treatment with nucleophile such as hydrazine to afford the peptide hydrazide A functionalized polymer to serve as a vehicle to deliver reactive functionality, such as an isocyanate. into the solution phase, would be highly useful in the development of combinatorial syntheses for ureas, carbamates, sulfonylureas, hydantoins and other heterocvciic svstems of biological importance High vields. high recoverv with few or no undesired side reactions stability, and a suitability for automation are requirements to satisfy the need in the field SUMMARY OF THE INVFNTION The invention comprises the production of the novel reagent by the reaction of a source of phosgene with the polvmer bound reagent wherein Z is the recurring part ot a carbonaceous polvmenc backbone or sidechain thereof. Y is a pendant group of the recurring part ot a carbonaceous polymeric backbone, and EWG is an electron withdrawing group The reagent is useful as a phosgene transfer reagent in the production of isocyanates The resulting composition is of the formula wherein Z is the recurring part of a carbonaceous polymeric backbone or side chain thereof and EWG is an electron-withdrawing group. Additionally, the invention includes a process for preparing a solid phase reagent of the formula wherein Z is the recurring part of a carbonaceous polymeric backbone or side chain thereof. EWG is an electron-withdrawing group and R | NH- is derived from an initial primary amine addition of the formula RτR 3 NH. The invention also includes a process tor preparing a non-symmetrical urea ot the formula O R i ^ Λ \R->R? wherein Ri- and RT are independently selected trom a roup consisting of optionally substituted alkyl or optionalh substuuied l and R-, is independently selected from a group consisting of optionalh substituted alkyl or optionally substimted aryl or hydrogen The non-svmmetrait.il urea is produced by contacting the solid phase reagent ot the formula wherein Z is the recurring part of a carbonaceous polymeric backbone or side chain thereof, EWG is an electron-withdrawing group and R | NH- is derived from an initial primary amine addition with an amine of the formula R2R3NH DETAILED DESCRIPTION OF THE INVENTION Applicant has invented a method to prepare a novel phosgenated oxime resin The resm is useful as a solid-phase phosgene transfer reagent to primary amines. In particular, it is useful for generating isocyanates upon thermolytic cleavage of the oxime-deπved carbamate As used herein the following terms may be used tor interpretation of the claims and specification scaffold - molecular framework on which functionality is presented trapping amine - amine used to trap isocvanate un.symmetπcai urea - urea derived from tw o different amines protic input - a molecule containing a heteroatom attached to a proton The use of solid phase reagents can overcome the limitations of the prior art by serving as a vehicle to deliver reactive tuncuonalitv . such as phosgene. onto desired sites ot a compound With one sue such as the isocvanate. attached to the solid-phase reagent, other sites can be manipulated at will Cleavage from the solid support will then allow the isocv anate to be further reacted to the desired end product The instant inv ention overcomes the problem of instabilπv ot the isocvanate bv the immobilization of the chloroformate as part of the solid phase reacent allow mi * it to be isolated, characterized and further reacted without the use ot an inert atmosphere Since the method provides lor high yields hn-h l ecovery with little or no undesired side reactions, high stabilπv . and is suitable tor automation, it is an effective tool in combinatorial synthesis The solid support used has the formula 011 wherein Z is the recurring part of the carbonaceous polvmenc backbone. Y is a pendant group of the recurring part ot a carbonaceous polvmenc backbone, and EWG is an electron-withdrawing group Λnv polvmer in which the oxime- deπved carbamate functionality can be added mav be used Suitable polymers include polystyrene and polyethylene Preferred is polystyrene, wherein Y is a pendant phenyl group of the polymer Any electron-withdrawing group (EWG) that is unreactive to phosgene may be used. Suitable groups include nitro, cyano. dinitro. tπfluoromethyl, di-tπfluoromethyl. and halogens Preferred is a nitro group Phosgenation can be performed with any source of phosgene Sources include phosgene gas and triphosgene. a commercially available solid trimer of phosgene The phosgenated oxime resin can be used to prepare unsymmetπcal ureas where the substitutions on the nitrogens are independently selected from the group consisting of hydrogen, optionally substimted alkyl, and optionally substituted aryl At least one of the four possible substituents on the nitrogen atoms must be hydrogen whose origin can be traced back to the primary amine used in the initial addition to the phosgenated oxime resin In the preparation of unsymmetπcal ureas, the trapping amine can be either primary optionally substimted alkyl or aryl or secondary optionally substimted alkyl The phosgenated oxime resin can also be used to prepare carbamates where an alcohol is used in the thermolytic cleavage trapping step instead ot an amme The method ot synthesis permits the scaffolding between the two inputs, namelv the primary amine and the trapping amine in the case of unsymmetπcal ureas, to be minimized In this case, the central scaf f olding ot the product is essentially a carbonyl group whose origin is traced back to the phosgene The high reactivity of phosgene is controlled bv the poi er support, which may be beads, film or other form having a high surface area This method provides a very versatile tool for the combinatorial chemist to tie prone inputs such as amines and alcohols) together on a relati elv small molecular scaffolding One reaction path is as follows O R, \ A \R,R- i H EQUIPMENT AND MATERIALS Toluene was distilled from sodium benzophenone ketyl and dichloromethane was distilled from phosphorus pentoxide prior to use. The solid phosgene equivalents, triphosgene and trhiophosgene were purchased from Aldrich and used directly Amines were also purchased from Aldnch and used directly without purification The oxime resin was prepared using Biobeads ® SX-1 (1 % crosshnked polystyrene) from Biorad (Hercules, CA). Microanalyses were carried out by Micro Analysis Inc. of Wilmington, Delaware. IR spectra were obtained with a Perkm-Elmer FT 1600. Low resolution mass spectra were obtained with a VG Tπo-2000 quadrapole mass spectrometer using the electrospray atmospheric pressure chemical lonization (APCI) techmque. HPLC analyses were performed on a Hewlett-Packard 1090 liquid chromatography system usmg a photodiode array detector and a Zorbax SB-C18 column. EXAMPLES The meaning of abbreviations is as follows "h" means hour(s), "min" means mιnute(s), "sec" means second(s), and "d" means day(s) EXAMPLE 1 PREPARATION OF OXIME RESIN The oxime resin was prepared by the method described in DeGrado, W F , Kaiser, E. T., J Org Chem 1982, 47, 3258-3261 Before use, the resin was pre-swelled in dichloromethane (75 mL) under an atmosphere of nitrogen, then allowed to shake overnight at room temperature 6 0 g (20 mmol) of triphosgene was weighed out in the drybox. dissolved in dichloromethane (75 mL) and added to 20 g (15 mmol, based on loading of 0 755 mmol/g resin) of the oxune resin Filtration of the loaded resin into a solution ot ethanol in dichloromethane (to quench the remaining phosgene) followed by washing with liberal amounts of dichloromethane (ca 350 mL) and drying under vacuum overnight afforded the ketoxime chloroformate IR (KBr) showed a strong peak at 1799 cm"l corresponding to the chloroformate Cl analysis indicated the loading to be 0.663 mmol/g resm corresponding to an 88% yield. EXAMPLES 2-9 Examples were performed following the general procedures outlined below Substrates, products and results are given in Table 1 1ST AMINE ADDITION Phosgenated resm (3 0 mmol) was weighed into a 60 mL bottle Amine (H 2 NR- , 9.24 mmol, 3 eq ) was weighed out and dissolved in dry dichloromethane (50 mL). Addition of the dichloromethane solution to the resin resulting swelling of the resin and the resulting mixture was sealed and vortexed overnight at room temperature Filtration of the resin followed by liberal washing with dichloromethane and then methanol (ca 500 mL total) and drying under high vacuum overnight afforded urea-functionalized oxime resm. Verification of complete addition was determined by loss of the chloroformate peak and presence of the carbamate carbonyl peak between 1750 and 1760 cm"' in the IR spectrum These resms were taken directly to the thermolytic cleavage without any further characterization THERMOLYTIC CLEAVAGE AND TRAPPING AMINE ADDITION Primary amine-functiona zed resin (0 5 mmol) was weighed into a 20 mL vial and swelled with dichloromethane until saturated (ca. 6 mL) Amine (NHR R 3 , 0.55 mmol, 1 1 eq. of non-volatile amines or 2 0 mmol, 4 eq. of volatile amines) was added and the total volume was taken to 18 mL with toluene The vial was then sealed and heated on a vortexor heating block to 75 °C overnight The mixture was allowed to cool to room temperature and the resin was removed by filtration and washed with dichloromethane (20 mL) followed by methanol (10 mL) three consecutive times The combined filtrates were evaporated to dryness to afford the urea product which was characterized by mass spectroscopy directly without any purification The low resolution mass spectra were obtained with a VG Tπo-2000 quadrapole mass spectrometer using the electrospray atmospheric pressure chemical lonization (APCI) techmque Yields were also determined on the unpuπfied product Purity analysis was performed by HPLC on aromatic-containing urea products HPLC analyses were performed on a Waters 2010 liquid chromatography system using a photodiode array detecotr and a Vydac C18 colu 2 1 x 150 mm, starting at 100% water/0.01 % TFA - > 100% acetonιtrιle/0 01 c TFA Results are indicated in Table 1 EXAMPLE 10 The reaction was performed as in the Examples above, except that a Nauthus 2400 automated synthesizer (Argonaut Technologies, Inc.. San Carlos, CA) was used to examine the dependence ot yield on cleavage temperature The individual reactor temperature of the cleavage step was independently controlled from 50°C to 120°C, and the yield plotted versus temperature These results are shown in Table 2 TABLE 1 10 TABLE 2 Isolated Yield of Cyclohexyl-4-Biphenylurea as a Function of Temperature % Yield Temperature (°C)

Claims: We claim: 1. The process for preparing a solid phase reagent useful in chemical synthesis comprising: reacting an excess of phosgene with a ketoxime of the formula wherein Z is the recurring part of a carbonaceous polymeric backbone or side chain thereof and EWG is at least one electron-withdrawing group, to produce the corresponding oxime-derived chloroformate. 2. A composition of matter of the formula wherein Z is the recurring part of a carbonaceous polymeric backbone or side chain thereof and EWG is an electron withdrawing group. 3. A solid phase reagent is of the formula wherein Z is the recurring part of a carbonaceous polymeric backbone or side chain thereof, EWG is an electron-withdrawing group and R|NH- is derived from an initial primary amine addition of an amine of the formula R 2 R3NH. 4. A process for preparing a non-symmetrical urea of the formula wherein R \ and R 2 are independently selected from a group consisting of optionally substituted alkyl or optionally substituted aryl and R 3 is independently selected from a group consisting of optionally substituted alkyl or optionally substituted aryl or hydrogen, the process comprising contacting the solid phase reagent ot the formula wherein Z is the recurring part of a carbonaceous polymeric backbone or side chain thereof, EWG is an electron-withdrawing group and R|NH- is derived from an initial primary ammc addition with an amine of the tormula R2R3NH.

Inventors: SCIALDONE MARK ANDREW, SCIALDONE, MARK, ANDREW
Applicants: DU PONT, SCIALDONE MARK ANDREW, E.I. DU PONT DE NEMOURS AND COMPANY, SCIALDONE, MARK, ANDREW
Application year: 1997
Main classification: C08F8
IPC codes: C07B43, C07B61, C07C273, C07C275, C07D213, C07D295, C07D307, C07D317, C07D405, C08F8