WO 2005/100366 PCT/US2005/012030 PROLINE CCI-779 (PROLINE-RAPAMYCIN 42-ESTER WITH 2,2-BIS (HYDROXYMETHYL) PROPIONIC ACID ) AND TWO-STEP ENZYMATIC SYNTHESIS OF PROLINE CCI-779 AND CCI-779 USING MICROBIAL LIPASE BACKGROUND OF THE INVENTION Rapamycin 42-ester with 2,2-bis(hydroxymethyI) propionic acid (CCI-779) is an ester derivative of rapamycin which has demonstrated significant inhibitory effects on tumor growth in both in vifro and in vivo models. The preparation and use of hydroxyesters of rapamycin, including CCI-779, have been described in US Patent Nos.: 5,362,718 and 6,277,983. Esterification of rapamycin at the 42-position was previously conducted by directly reacting rapamycin with acylating agents. However, as rapamycin contains two secondary hydroxyl groups at positions 31 and 42, attempts to discriminate between these two functional centers in order to achieve a selective synthesis of 42-monoacylated product still posed a difficult challenge. Currently, a regioselective process for the preparation of CCI-779 involves at least five steps (US Patent No. 6,277,983, International Patent Publication No. WO 01/23395). First, rapamycin is treated with a silylation agent to form rapamycin 31,42-bis-silyl ether, and then the 42-silyl ether protection group is selectively removed to provide rapamycin 42-OH-31-silyl ether. This freed 42-OH was then acylated with 2,4,6-trichlorobenzyl mixed anhydride of 2,2,5-trimethyl[l,3-dioxane]-5-carboxylic acid and two subsequent deprotection steps furnish the desired CCI-779. CCI-779 binds to and forms a complex with the cytoplasmic protein FKBP, which inhibits an enzyme, mTOR (mammalian target of rapamycin, also known as FKBP 12-rapamycin associated protein [FRAP]). Inhibition of mTOR's kinase activity inhibits a variety of signal transduction pathways, including cytokine-stimulated cell proliferation, translation of mRNAs for several key proteins that regulate the Gl phase of the cell cycle, and IL-2-induced transcription, leading to inhibition of progression of the cell cycle from Gl to S. CCI-779 has been demonstrated to be effective in multiple applications, including inhibition of central nervous system cancer, leukemia, breast cancer, prostate cancer, melanoma, gliomas, and glioblastoma. 1 WO 2005/100366 PCT/US2005/012030 What are needed are more efficient methods for regiospecific production of CCI-779, and analogs thereof. SUMMARY OF THE INVENTION The present invention provides a proline analog of CCI-779 (proline-rapamycin 42-ester with 2,2-bis(hydroxymethyl)propionic acid or proline-CCI-779) and methods of synthesizing same. Proline-CCI-779 is an active drug substance useful in oncology and other associated indications (immunosuppression, anti-inflammatory, anti-proliferation and anti-tumor). In one aspect, the synthesis of proline-CCI-779 is accomplished through bis-silylation of proline rapamycin, mono-de-protecting 31,42-bis-trimethylsilyl proline rapamycin, and acylating the mono-silyl proline rapamycin followed by hydrolysis. In another aspect, the invention provides a two-step enzymatic process involving a regiospecific acylation of rapamycin, using a microbial lipase and an activated ester derivative of 2J2-bis(hydroxymethyl)propionic acid in an organic solvent, followed by deprotection to give CCI-779. In another aspect, the method of the invention permits synthesis of proline CCI-779 from proline-rapamycin, a closely related compound of rapamycin within the rapamycin family. Other aspects and advantages of the invention will be readily apparent to one of skill in the art. DETAILED DESCRIPTION OF THE INVENTION This invention describes a proline analog of rapamycin dihydroxyesters and uses thereof. In one embodiment, the invention provides a proline CCI-779, which is characterized by the core structure: 2 WO 2005/100366 PCT/US2005/OI2030 The invention further provides a method of synthesizing the proline analog of rapamycin dihydroxyesters. In one embodiment, a proline rapamycin is used as a starting material. Rapamycin and its preparation are described in US Patent No. 3,929,992, issued December 30,1975. Alternatively, rapamycin may be purchased commercially [Rapamune®, Wyeth]. Proline rapamycin and its preparation have been described. See, e.g., European Patent No. 0589703. In one embodiment, proline rapamycin is bis-silylated to form 31,42-bis-trimethylsilyl proline rapamycin. Silylating agents that can be used for this transformation include, e.g., commercially available chloroalkylsilanes, such as chlorotrimethylsilane, chlorotriethylsilane, chlorotripropylsilane or chlorotriisopropylsilane. In one embodiment, the silylating agent is chlorotrimethylsilane. Although bulkier silylating agents can be used, such agents require more time to deprotect in acidic media in subsequent reactions. Furthermore, the longer the reaction time in acidic media, the more degradation by-products are formed. In another embodiment, the silylating reaction is performed with trimethylsilyl chloride with a suitable organic base and a suitable organic solvent at cold temperatures to form 31,42-bis-trimethylsilyl proline rapamycin. In one embodiment, the reaction temperature is about 0 to 5°C. In other embodiments, the reaction is conducted at lower temperatures, resulting in a longer reaction time. Suitable organic solvents including, e.g., DMF, can be readily selected. In one embodiment, ethyl acetate is the solvent Similarly, suitable 3 WO 2005/100366 PCT/US2005/012030 organic bases can be readily selected from among those known in the art, e.g., imidazole, 1-methyl imidazole, triallcylamines and N,N-diisopropylethylamine. In one embodiment) the base is imidazole, resulting in a completed reaction in less than 1 hour, under the conditions described herein. Mono-deprotection at the 42-position at 0 to 5°C under dilute acid conditions provides 31-trimethylsilyl proline rapamycin. Acylation of mono-silyl proline rapamycin is achieved using 2,4,6-trichlorobenzyl mixed anhydride of 2,2,5-trimethyl[l,3-dioxane]-5-carboxylic acid in the presence of 4-dimethylaminopyridine or a similar catalyst in methylene chloride at -15 to -10°C to give an intermediate. In another embodiment, mono-silyl proline rapamycin is coupled with the acid chloride of 2,2,5-trirnethyl[l,3-dioxane]-5-carboxylic acid in the presence of an organic base catalyst such as 4-dimethylaminopyridine. Other organic catalysts can be substituted for 4-dimethylaminop3'ridine, including, e.g., other tertiary organic bases such as N,N-dimethylaniline, pyridine, triethylamine, and diisopropylethylamine, among others. In one embodiment, the solvent for the acyiation reaction is methylene chloride. In other embodiments, THF, diethylether or t-butyl methyl ether is used. The reaction can be performed at temperatures less than 0°C. In one embodiment, the reaction is performed at -10°C, or lower. In one embodiment, mono-silyl proline rapamycin is coupled with a mixed anhydride and dimethylaminopyridine in methylene chloride at -12°C to give an intermediate product. In another embodiment, acylation may be performed as described in US Patent Application Publication No. US 2005/0033046 Al (published February 10, 2005). Accordingly, in one embodiment, acylation of mono-silyl proline rapamycin is achieved using 2,4,6-trichlorobenzyl mixed anhydride of a phenylborinane in the presence of 4-dimethylaminopyridine or a similar catalyst in methylene chloride at -11 to -5°C to give an intermediate. In another embodiment, the phenylborinane is 2-phenyl-l,3,2-dioxoborinane-5-carboxylic acid. In yet another embodiment, the phenylborinane is a 2-phenyl-l,3,2-dioxaborinan-4-yl, wherein the phenyl is optionally substituted. In still another embodiment, the phenylborinane is 5-methyl-2-phenyl-l,3,2-dioxaborinane-5-carboxylic acid. 4 WO 2005/1(10366 PCT/US2005/012030 In a further embodiment, the phenyl group is substituted with an alkyl, such as a C1, C2, C3, C4, C5, or C6alkyl. Other aryl- (including phenyl-) boronic acids maybe used in this reaction. These include mono, di, and tri-substituted arylboronic acids in which Hie substituents are the same or different Substituents on the aryl group include halogen, alkyl, alkoxy, aryloxy (e.g., phenoxy), aralkyl, nitro, cyano, and fused phenyl such as napthalylboronic acid. The term alkyl when used as a group or part of a group such as alkoxy or aralkyl includes -alkyl moieties of 1 to 12 carbon atoms, e.g., 1-6 carbon atoms. The term aryl as a group or part of a group, e.g., aralkyl or aryloxy, means an aromatic group including those of 6-10 carbon atoms, e.g., phenyl or napthyl. In one embodiment, the solvent for the acylation reaction is methylene chloride. In other embodiments, THF, diethylether or t-butyl methyl ether is used. The reaction can be performed at temperatures less than 0°C. In one embodiment, the reaction is performed at -10°C, or lower. In one embodiment, mono-silyl proline rapamycin is coupled with a mixed anhydride and dimethylaminopyridine in methylene chloride at -12°C to give intermediate product. Mild acidic hydrolysis in a suitable solvent (e.g. THF) and temperature provides the proline analog of CCI-779. In one embodiment, a dilute inorganic acid such as sulfuric, hydrochloric or phosphoric acid is used. In another embodiment, dilute aqueous sulfuric acid is used. The concentrations range from 0.1 N to about 3 N. In one embodiment, the concentration is 2 N, as under these conditions both the acetal and silyl protecting groups are hydrolyzed at the same time. Under more dilute acidic conditions, hydrolysis takes longer to complete. In one embodiment, this step is carried out at 25°C or below, or about 0 to 5°C. Purification can be accomplished by methods known to those of skill in the art including, e.g., chromatography followed by a final crystallization {e.g., by ether treatment) to furnish a purified proline CCI-779. In another embodiment, this invention provides a novel process for the preparation of rapamycin 42-ester with 2,2-bis(hydroxymethyl)propionic acid (CCI-779) and proline-CCI-779. The process is described below for the preparation of CCI-779. However, proline-CCI-779 may be prepared by the same process from proline rapamycin, as described below. 5 WO 2005/100366 PCT/US2005/012030 The synthesis requires two steps. The first step is a microbial lipase-catalyzed acylation of rapamycin with an activated ester of 2,2-bis(hydroxymethyl)propionic acid derivative in an organic solvent. This reaction is highly regioselective, resulting in the exclusive formation of mono-42-acylated product (i.e., protected CCI-779), in nearly quantitative yield. Subsequent deprotection furnishes CCI-779 in excellent overall yield. Compared with chemical preparation, this chemo-enzymatic route offers a much shorter procedure with higher yield. Further, this method does not require any steps to protect the rapamycin's 31-OH group. The following scheme illustrates this enzymatic preparation of CCI-779. The examples that follow are intended to exemplify the claimed invention, and should not be construed as limiting the disclosure or the claimed invention. Rapamycin and its preparation are described in US Patent No. 3,929,992, issued December 30, 1975. Alternatively, rapamycin may be purchased commercially [Rapamune®, Wyeth]. Identification of a suitable activated ester of 2,2-bis(hydroxymethyl) propionic acid side chain has been found to be the key to the success of this lipase-catalyzed acylation. The inventors have found that the corresponding enol esters provide the highest activity and the best yield, especially the vinyl ester. However, other acylation reagents such as methyl, ethyl esters, 2,2,2-trichloroethyl, 2,2,2-trifluoroethyl esters and N-succinimidyl ester may also be used. The protecting group at propionic acid's two bis-hydroxyl groups also plays an important role in the reaction. In one embodiment, cyclic ketals and cyclic boronates are used. However, other protecting groups can be selected from among protecting groups small enough to accommodate this side chain into the enzyme's active site. The activated ester of 2,2-bis(hydroxymethyl) propionic acid has the structure of formula below 6 WO 2005/100366 PCT/US2005/012030 wherein R is hydrogen or methyl, Rj and R2 are hydrogen, or together form a ketal with the structure, R3, R4 are each, independently, hydrogen, C1-6 alkyl, either linear or branched, or together form C5.7 cycloalkyl or together form a cyclic boronate with the structure, /B~Rs, R5 is selected from methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl and phenyl. Vinyl ester (R = H) with isopropylidene ketal (I) or methyl boronate (II) protecting group has been selected to illustrate the process of this invention. In one embodiment, the first step of process of invention is performed by reacting rapamycin with a vinyl ester (I) or (II) in the presence of a lipase of microbial origin in a suitable organic solvent under optimal temperature for a certain period of time. As used herein, "microbial Upases", i.e., lipases with microbial origin, include enzymes which were originally isolated from a non-eukaryotic source, such as, Aspergillus niger, Candida antarctica, Candida rugosa, Mucor miehei, Pseudomonas cepacia, Pseudomonas fluorescens, Rhizopus delemar. However, the enzyme selected for use in the invention need not be directly isolated and purified from the original source, but can be prepared synthetically or recombinantly, or through other suitable means. A variety of these enzymes are available from some commercial sources. Further, these enzyme preparations can be used as crude, partially purified, purified or immobilized from different microbial origin under different trade names by various suppliers. In one embodiment, lipase PS-C "Amano" II, an immobilized form of lipase PS from Amano, is used in the method of the invention. However, other lipases can be selected for use in the invention. Such lipases provide a degree of conversion of rapamycin to protected CCI-779 intermediate of greater than 60%, greater than 75%, or 7 WO 2005/100366 PCT/US2005/012030 greater than 90%. In a further embodiment, such Upases avoid the formation of a significant amount of seco derivative resulting from lipase-catalyzed hydrolysis. The lipase is used in an effective catalytic amount, i.e., an amount which effectively catalyzes, at a reasonable rate of reaction, the acylation of 42-hydroxyl of rapamycin to form the protected CCI-779. Those skilled in the art will appreciate that the enzyme can be used in amounts of about 25 to about 300 wt% (relative to the amount of rapamycin). In one embodiment, the enzyme is used in amounts of about 50 to about 250 wt%, about 50 to about 200 wt%, or about 75 to about 150 wt%. Suitable organic solvents include, but are not limited to, toluene, tert-butyl methyl ether (TBME), ethyl ether, THF (tetrahydrofuran), MeCN, CH2C12, CHC13, iPr20, hexane, dioxane, or mixtures including these solvents. In one embodiment, TBME {tert-buty methyl ether) is used. It will be appreciated by those skilled in the art that the solvent is used in an amount which can effectively dissolve all or part of starting rapamycin at the beginning and allows the reaction to proceed at a reasonable rate. For example, a solvent, such as TBME. can be used in an amount of at least 4 wt volume (i.e, a volume that is in an excess of 4 times (4X) the amount of rapamycin) to about 10 wt volume, or about 5 to 8 wt volume. TBME may contain residual water (e.g., about 0.05%) which could decompose the rapamycin into a so-called, seco-derivative, a macro lactone-ring opened product. In order to minimize this side-reaction, a low amount of moisture is maintained in the reaction system. In one embodiment, an anhydrous solvent is used with a standard commercial preparation of the lipase catalyst, hi another embodiment, moisture can be controlled through adjusting the amount of water present in the lipase solution by adding a drying agent. In yet another embodiment, a molecular sieve can be used to control the moisture. Since a molecular sieve will slow the reaction down, more enzyme can be added to compensate, or a longer reaction time can be used. "Where a molecular sieve is used, a 5 A sieve is particularly desirable. However, other sieve sizes, including, 4 A and 3 A, among others, can be readily utilized. Suitable molecular sieves are available from a variety of commercial sources. In still another embodiment, drying agents such as MgSO4, Na2SO4, among others, can be used to control the moisture content. 8 WO 2005/100366 PCT/US2005/012030 The reaction is conducted at a temperature low enough to reduce the formation of unwanted by-product, but not so low as to require an unreasonably long reaction time. A suitable temperature for this enzymatic process can be in the range of about 20°C to about 75°C, about 30°C to 65°C, or about 40°C to 55°C. In one embodiment, the temperature for the reaction is permitted to proceed at 45°C when TBME is used as solvent. Under such conditions, the reaction can proceed virtually to completion (> 99% conversion) within 48 hours. However, lower or higher temperatures can be used, and the length of time for reaction varied, as described herein. In another embodiment, the reaction may be permitted to proceed for about 12 hours to 120 hours, 18 hours to 96 hours, 24 hours to 72 hours, or about 30 hours to 60 hours, as desired or needed. The length of time of the reaction is not a limitation on the present invention. In a further embodiment, the reaction is performed under N2 until all starting material is consumed. The reaction can be monitored by various techniques such as thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Alternatively, other monitoring methods can be used by one of skill in the art. In one embodiment, by mixing rapamycin, 100 wt% (relative to the amount of rapamycin) lipase PS-C "Amano" II and isopropylidene ketal protected vinyl ester of 2,2-bis(hydroxymethyl)propionic acid (I) in anhydrous TBME at 45 °C for 48 hours, after removing enzyme by filtration, ketal protected CCI-779 was obtained in >98% yield. In another embodiment, the process is conducted by mixing rapamycin, 160 wt% lipase PS-C "Amano" II and methyl boronate protected vinyl ester of 2,2-bis(hydroxymethyl)propionic acid (II) in anhydrous terf-butyl methyl ether (TBME) at 45 °C for 60 hours, after removing enzyme by filtration, cyclic methyl boronate protected CCI-779 was obtained in high yield based on the recovered rapamycin. Following the enzymatic installation of either ketal- or boronate-protected 2,2-bis(hydroxymethyl)propionic acid into the 42-position of rapamycin, CCI-779 can be obtained by subsequent de-protection of the resulting intermediate. In the case of the boronate derivative, removal of boronate protecting group can be realized by using an alcoholic solvent. In this embodiment of the invention, a suitable alcoholic solvent can be readily selected from the group consisting of methanol (MeOH), ethanol, propanol, isopropanol, butanol, iso-butanol, ethylene glycol, 1,3-propanediol and 9 WO 2005/100366 PCT/US2005/012030 2-methylpentane-2,5-diol, or a mixture of these solvents. In one embodiment, the crude product resulting from the enzyme reaction is dissolved in MeOH and the boronate moiety in CCI-779 forms the volatile dimethyl boronate by exchange with MeOH is then evaporated along with solvent under reduced pressure. The remaining residue contains desired CCI -779 along with some unreacted rapamycin, winch can be separated by general methods such as silica gel chromatography. The removal of the ketal protecting group can be accomplished under mildly acidic conditions. In general, the procedure published in US Patent No. 6,277,983 and documents cited therein can be followed. In one embodiment, the deprotection is carried out in a single phase aqueous acid/organic solvent system, e.g., diluted sulfuric acid in tetrahydrofuran (THF), such as 2 N H2SO4/THF at about 0 to 5°C. However, this reaction can take about 3 days or more to complete and solvent extraction is needed to recover the product from aqueous media after reaction is complete. In another embodiment, this acid promoted deprotection can be performed in other water miscible solvents such as acetonitrile (MeCN), n-propanol and iso-propanol. These solvents can be used either alone or as a mixture between acetonitrile and n-propanol or iso-propanol. The ratio of mixed solvent can be varied as described herein, from about 5 parts of acetonitrile with 1 part of propanol (v/v), to about 1 part of acetonitrile with 5 parts of propanol. This ratio is not the limitation of the present invention. When the above solvents or their mixtures are used as reaction medium, in one embodiment aqueous sulfuric acid is used, as it minimizes the formation of impurities generated when other acids, such as aqueous hydrochloric acid, are employed, as described in US Patent No. 5,362,718. The concentration of aqueous sulfuric acid can be in the range of 3 N to 0.25 N, about 2 N to 0.35 N, or about 1.5 N to 0.5 N. The reaction may be carried out at a temperature about 25 °C or below, about -5°C to about 10°C, or about 0°C to about 5°C. When the reaction is complete, the crude product can be recovered by solvent extraction as described in US Patent No. 6,277,983 (International Patent Publication No. WO 01/23395), or via precipitation by adding the reaction mixture to an ice-cold (0°C to 5°C) phosphate buffer. In one embodiment, the concentration of phosphate buffer is in the range of about 2 M to 0.05 M, 1 M to 0.1 M, or 0.5 M to 0.15 M, with a pH value in the range of 6 to 9, or 7.5 to 8.5. In one embodiment, the deprotection is carried out in n- 10 WO 2005/100366 PCT/US2005/012030 propanol with 1.2 N H2SO4 at 0 °C to 5 °C and the reaction is completed within 24 h, the crude is then recovered as a off-white powder by adding reaction mixture to phosphate buffer (0.5 M, pH 8) cooled with an ice-water bath. In another embodiment, the deprotection is carried out in a mixed solvent of MeCN-n-propanol (2.5/1.5 v/v) at 0°C to 5°C, the reaction was done in 28 hours in the presence of 0.6 N H2SO4, and the product is recovered as an off-white powder by adding reaction mixture to phosphate buffer (0.25 M, pH 7.8) In another embodiment, CCI-779 could be obtained by direct hydrolysis of enzymatic reaction mixture using aqueous 2 N H2SO4 in THF without the isolation of crude ketal-protected CCI-779. In this process, the enzymatic reaction is carried out as described above. When reaction is complete, the enzyme is filtered off and washed with 2 volumes of THF, the mixture is then concentrated to a certain volume and diluted with THF. Following treatment with 2N H2SO4 at 0-5°C for a certain period of time, CCI-779 can be isolated in high yield. The synthetic route of the invention provides several distinct advantages over the synthetic methodology published in US Patent Nos. 5,362,718 and 6,277,983. These advantages include ease of processing, with only two-step manipulation involved, and improved overall yields of the desired 42-ester. For example, the synthetic methodology described in US Patent No. 5,362,718 provides the isopropylidene ketal-protected CCI-779 in a 35% yield, and the synthetic methodology described in US Patent No. 6,277,983 provides 85% yield, whereas the two-step enzymatic process described herein furnishes the product in nearly quantitative yield. In another embodiment, this provides a process for preparing proline-CCI-779, a closely related compound to CCI-779, from proline-rapamycin by the same enzymatic process described herein. Proline-rapamycin, a minor component from rapamycin fermentation crude, is only structurally different from an amino acid unit, i.e., instead of pipecolinic acid in rapamycin, it is replaced by proline. Proline rapamycin, proline-CCI-779 and its derivatives are described in EP 589703. 11 WO 2005/100366 PCT/US2005/012030 The resulting CCI-779 and proline CCI-779 prepared according to this invention is useful in pharmaceutical compositions. Such compositions can be formulated by any suitable method described in the art for rapamycin or derivatives thereof. Oral formulations containing the active compounds as described herein may comprise any conventionally used oral forms, including tablets, capsules, buccal forms, troches, lozenges and oral liquids, suspensions or solutions. Capsules may contain mixtures of the active compound(s) with inert fillers and/or diluents such as the pharmaceutically acceptable starches (e.g., corn, potato or tapioca starch), sugars, artificial sweetening agents, powdered celluloses, such as crystalline and microcrystalline celluloses, flours, gelatins, gums, etc. Useful tablet formulations may be made by conventional compression, wet granulation or dry granulation methods and utilize pharmaceutically acceptable diluents, binding agents, lubricants, disintegrants, surface modifying agents (including surfactants), suspending or stabilizing agents, including, but not limited to, magnesium stearate, stearic acid, talc, sodium lauryl sulfate, microcrystalline cellulose, carboxymethylcellulose calcium, polyvinylpyrrolidone, gelatin, alginic acid, acacia gum, xanthan gum, sodium citrate, complex silicates, calcium carbonate, glycine, dextrin, sucrose, sorbitol, dicalcium phosphate, calcium sulfate, lactose, kaolin, mannitol, sodium chloride, talc, dry starches and powdered sugar. In one embodiment, surface modifying agents include nonionic and anionic surface modifying agents. Representative examples of surface modifying agents include, but are not limited to, poloxamer 188, benzalkonium chloride, calcium stearate, cetostearyl alcohol, cetomacrogol emulsifying wax, sorbitan esters, colloidal silicon dioxide, phosphates, sodium dodecylsulfate, magnesium aluminum silicate, and triethanolamine. Oral formulations herein may utilize standard delay or time release formulations to alter the 12 WO 2005/100366 PCT/US2005/012030 absorption of the active compound(s). The oral formulation may also consist of administering the active ingredient in water or a fruit juice, containing appropriate solubilizers or emulsifiers as needed. In one embodiment, oral formulations for raparnycin 42-cstcr with 3-hydroxy-2-(hydroxymethyl)-2-methylpropionic acid are described in US Published Patent Application No. US 2004-0077677 Al (also US Patent Application No. 10/663,506), which are hereby incorporated by reference. Such an oral formulation contains a granulation prepared using a wet granulation process. Similar oral formulations can be prepared using the proline-CCI-779 of the invention. In some cases it may be desirable to administer the compounds directly to the airways in the form of an aerosol. The compounds may also be administered parenterally or intraperitoneally. Solutions or suspensions of these active compounds as a free base or pharmacologically acceptable salt can be prepared in water suitably mixed with a surfactant such as hydroxy-propylcellulose. Dispersions can also be prepared in glycerol, liquid polyethylene glycols and mixtures thereof in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases, the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (e.g., glycerol, propylene glycol and liquid polyethylene glycol), suitable mixtures thereof, and vegetable oils. In one embodiment, injectable formulations are described in US Patent Publication No. US 2004-0167152 Al (also US Patent Application No. 10/626,943), which are hereby incorporated by reference. Similar parenteral formulations for proline-CCI-779 may be readily prepared. 13 WO 2005/100366 PCT/US2005/012030 In another embodiment, the injectable formulation useful in the invention provides a CCI-779 or a proline-CCI-779 cosolvent concentrate containing a parenterally acceptable solvent and an antioxidant as described above and a parenteral formulation containing a CCI-779 or a proline-CCI-779, composed of a CCI-779 or a proline-CCT-779, a parenterally acceptable cosolvent, an antioxidant, a diluent solvent, and a surfactant. Any given formulation useful in this invention may contain multiple ingredients of each class of component. In one embodiment, a parenterally acceptable solvent can include a non-alcoholic solvent, an alcoholic solvent, or mixtures thereof. Examples of suitable non-alcoholic solvents include, e.g., dimethylacetamide, dimethylsulfoxide or acetonitrile, or mixtures thereof. "An alcoholic solvent," may contain one or more alcohols as the alcoholic solvent component of the formulation. Examples of solvents useful in the formulations invention include, without limitation, ethanol, propylene glycol, polyethylene glycol 300, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, or mixtures thereof. These cosolvents are particularly desirable because degradation via oxidation and lactone cleavage occurs to a lower extent for these cosolvents. Further, ethanol and propylene glycol can be combined to produce a less flammable product, but larger amounts of ethanol in the mixture generally result in better chemical stability. A concentration of 30 to 100% v/v of ethanol in the mixture is preferred. In another embodiment, the stability of a CCI-779 or a proline-CCI-779 in parenterally acceptable alcoholic cosolvents is enhanced by addition of an antioxidant to the formulation. Acceptable antioxidants include, but are not limited to, citric acid, d,l-