Rapamycin (Sirolimus)

(3S,6R,7E,9R,10R,12R,14S,15E,17E,19​E,21S,23S,26R,27R,34aS)-9,10,12,13,14,21,22,23,24,​25, 26,27,32,33,34,34a-Hexadecahydro-9,27-dihydroxy-3-​[(1R)-2-[(1S,3R,4R)-4-hydroxy-3-methoxycyclohexyl]​-1-methylethyl]-10,21-dimethoxy-6,8,12,14,20,26-he​xamethyl-23,27-epoxy-3H-pyrido[2,1-c][1,4]oxaazacy​clohentriacontine-1,5,11,28,29(4H,6H,31H)-pentone

Wyeth Pharmaceuticals (Originator)

M.Wt:914.18

Formula:C₅₁H₇₉NO₁₃

53123-88-9 cas no

Antifungal and immunosuppressant. Specific inhibitor of mTOR (mammalian target of Rapamycin). Complexes with FKBP-12 and binds mTOR inhibiting its activity. Inhibits interleukin-2-induced phosphorylation and activation of p70 S6 kinase. Induces autophagy in yeast and mammalian cell lines.

Rapamycin is a triene macrolide antibiotic, which demonstrates anti-fungal, anti-inflammatory, anti-tumor and immunosuppressive properties. Rapamycin has been shown to block T-cell activation and proliferation, as well as, the activation of p70 S6 kinase and exhibits strong binding to FK-506 binding proteins. Rapamycin also inhibits the activity of the protein, mTOR, (mammalian target of rapamycin) which functions in a signaling pathway to promote tumor growth. Rapamycin binds to a receptor protein (FKBP12) and the rapamycin/FKB12 complex then binds to mTOR and prevents interaction of mTOR with target proteins in this signaling pathway. Rapamycin name is derived from the native word for Easter Island, Rapi Nui.

A macrolide compound obtained from Streptomyces hygroscopicus that acts by selectively blocking the transcriptional activation of cytokines thereby inhibiting cytokine production. It is bioactive only when bound to IMMUNOPHILINS. Sirolimus is a potent immunosuppressant and possesses both antifungal and antineoplastic properties.

Sirolimus (INN/USAN), also known as rapamycin, is an immunosuppressant drug used to prevent rejection in organ transplantation; it is especially useful in kidney transplants. It prevents activation of T cells and B cells by inhibiting their response to interleukin-2 (IL-2). Sirolimus is also used as a coronary stent coating. Sirolimus works, in part, by eliminating old and abnormal white blood cells.^{[citation needed]} Sirolimus is effective in mice with autoimmunity and in children with a rare condition called autoimmune lymphoproliferative syndrome (ALPS).

sirolimus

A macrolide, sirolimus was discovered by Brazilian researchers as a product of the bacterium Streptomyces hygroscopicus in a soil sample fromEaster Island^[1] — an island also known as Rapa Nui.^[2] It was approved by the FDA in September 1999 and is marketed under the trade nameRapamune by Pfizer (formerly by Wyeth).

Sirolimus was originally developed as an antifungal agent. However, this use was abandoned when it was discovered to have potent immunosuppressive and antiproliferative properties. It has since been shown to prolong the life of mice and might also be useful in the treatment of certain cancers.

Unlike the similarly named tacrolimus, sirolimus is not a calcineurin inhibitor, but it has a similar suppressive effect on the immune system. Sirolimus inhibits the response tointerleukin-2 (IL-2), and thereby blocks activation of T and B cells. In contrast, tacrolimus inhibits the secretion of IL-2.

The mode of action of sirolimus is to bind the cytosolic protein FK-binding protein 12(FKBP12) in a manner similar to tacrolimus. Unlike the tacrolimus-FKBP12 complex which inhibits calcineurin (PP2B), the sirolimus-FKBP12 complex inhibits themammalian target of rapamycin (mTOR, rapamycin being an older name for sirolimus) pathway by directly binding the mTOR Complex1 (mTORC1).

mTOR has also been called FRAP (FKBP-rapamycin associated protein), RAFT (rapamycin and FKBP target), RAPT1, or SEP. The earlier names FRAP and RAFT were coined to reflect the fact that sirolimus must bind FKBP12 first, and only the FKBP12-sirolimus complex can bind mTOR. However, mTOR is now the widely accepted name, since Tor was first discovered via genetic and molecular studies of sirolimus-resistant mutants of Saccharomyces cerevisiae that identified FKBP12, Tor1, and Tor2 as the targets of sirolimus and provided robust support that the FKBP12-sirolimus complex binds to and inhibits Tor1 and Tor2.

rapamycin

Unlike the similarly named tacrolimus, sirolimus is not a calcineurin inhibitor, but it has a similar suppressive effect on the immune system. Sirolimus inhibits the response to interleukin-2 (IL-2), and thereby blocks activation of T and B cells. In contrast, tacrolimus inhibits the secretion of IL-2.

The mode of action of sirolimus is to bind the cytosolic protein FK-binding protein 12 (FKBP12) in a manner similar to tacrolimus. Unlike the tacrolimus-FKBP12 complex which inhibits calcineurin (PP2B), the sirolimus-FKBP12 complex inhibits the mammalian target of rapamycin(mTOR, rapamycin being an older name for sirolimus) pathway by directly binding the mTOR Complex1 (mTORC1).

mTOR has also been called FRAP (FKBP-rapamycin associated protein), RAFT (rapamycin and FKBP target), RAPT1, or SEP. The earlier names FRAP and RAFT were coined to reflect the fact that sirolimus must bind FKBP12 first, and only the FKBP12-sirolimus complex can bind mTOR. However, mTOR is now the widely accepted name, since Tor was first discovered via genetic and molecular studies of sirolimus-resistant mutants of Saccharomyces cerevisiae that identified FKBP12, Tor1, and Tor2 as the targets of sirolimus and provided robust support that the FKBP12-sirolimus complex binds to and inhibits Tor1 and Tor2.

SIROLIMUS

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].

Rapamycin (Sirolimus) is a 31-member natural macrocyclic lactone [C51H79N1O13; MWt=914.2] produced by Streptomyces hygroscopicus and found in the 1970s (U.S. Pat. No. 3,929,992; 3,993,749). Rapamycin (structure shown below) was approved by the Food and Drug Administration (FDA) for the prophylaxis of renal transplant rejection in 1999.

Rapamycin resembles tacrolimus (binds to the same intracellular binding protein or immunophilin known as FKBP-12) but differs in its mechanism of action. Whereas tacrolimus and cyclosporine inhibit T-cell activation by blocking lymphokine (e.g., IL2) gene transcription, sirolimus inhibits T-cell activation and T lymphocyte proliferation by binding to mammalian target of rapamycin (mTOR). Rapamycin can act in synergy with cyclosporine or tacrolimus in suppressing the immune system.

Rapamycin is also useful in preventing or treating systemic lupus erythematosus [U.S. Pat. No. 5,078,999], pulmonary inflammation [U.S. Pat. No. 5,080,899], insulin dependent diabetes mellitus [U.S. Pat. No. 5,321,009], skin disorders, such as psoriasis [U.S. Pat. No. 5,286,730], bowel disorders [U.S. Pat. No. 5,286,731], smooth muscle cell proliferation and intimal thickening following vascular injury [U.S. Pat. Nos. 5,288,711 and 5,516,781], adult T-cell leukemia/lymphoma [European Patent Application 525,960 A1], ocular inflammation [U.S. Pat. No. 5,387,589], malignant carcinomas [U.S. Pat. No. 5,206,018], cardiac inflammatory disease [U.S. Pat. No. 5,496,832], anemia [U.S. Pat. No. 5,561,138] and increase neurite outgrowth [Parker, E. M. et al, Neuropharmacology 39, 1913-1919, 2000].

Although rapamycin can be used to treat various disease conditions, the utility of the compound as a pharmaceutical drug has been limited by its very low and variable bioavailability and its high immunosuppressive potency and potential high toxicity. Also, rapamycin is only very slightly soluble in water. To overcome these problems, prodrugs and analogues of the compound have been synthesized. Water soluble prodrugs prepared by derivatizing rapamycin positions 31 and 42 (formerly positions 28 and 40) of the rapamycin structure to form glycinate, propionate, and pyrrolidino butyrate prodrugs have been described (U.S. Pat. No. 4,650,803). Some of the analogues of rapamycin described in the art include monoacyl and diacyl analogues (U.S. Pat. No. 4,316,885), acetal analogues (U.S. Pat. No. 5,151,413), silyl ethers (U.S. Pat. No. 5,120,842), hydroxyesters (U.S. Pat. No. 5,362,718), as well as alkyl, aryl, alkenyl, and alkynyl analogues (U.S. Pat. Nos. 5,665,772; 5,258,389; 6,384,046; WO 97/35575).

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Several total synthese of rapamycin have been reported^3,4as well as many fragments and part-syntheses. Rapamycin is a complicated molecule comprising a 31-membered ring including a pipecolinyl group and pyranose ring, a conjugated triene system and a tri-carbonyl region. It also has 15 chiral centres, meaning the number of possible stereoisomers is enormous. The synthesis of rapamycin therefore presents a huge challenge to synthetic chemists.

In the following synthesis, published in three separate papers^5,6,7two fragments of C10-C21 and C22-C42 are prepared separately, before being combined to give the total synthesis of rapamycin. Only the main outline of the synthesis will be shown as it is too long and complicated to show in great detail. For the full experimental details of the synthesis see the literature (ref. nos. given above).

In the retro-synthesis shown the molecule is disconnected at the ester group next to carbon 1 and the C₂₁-C₂₂ double bond of the triene to give the synthetic precursors 2 and 3. Further disconnections of 3 will be shown later. First the C₁₀-C₂₁ fragment is synthesised.

Synthesis of C10-C21 fragment

The synthesis uses (R)-methyl 3-hydroxy-2-methylpropionate (8) as a starting material.

The starting material 8 is converted to an alcohol by a four-step process; protection of the alcohol as aTHP ether followed by reduction, ether formation and deprotection steps. Substitution of the hydroxyl group in the product for a bromine leads to the formation of the bromide 9. Reaction of 9 with methyl acetoacetate gave ester 10.

Catalytic reduction of 10 using the conditions of Noyori produced ester 11, which was then converted to its Weinreb amide 12. Overall, compound 12 was produced in 54% yield from an inexpensive starting material. Vinyl bromide 13 was metalated with t-BuLi and the resulting vinyllithium was combined with 12 and the PMB-protecting group was removed to give 14. The remaining carbonyl group in 14 was selectively reduced to a hyrdoxy group. In order to differentiate the 1,3-diol a lactol was formed, where one hydroxy group ended up in the ring. To acheive this an oxidation was performed using RuCl₂(PPh₃)₃ resulting in formation of a lactol. The two remaining alcohol groups could then be methylated using MeI forming 15.

The lactol ring opening was achieved using TiCl₄ and thiol HS(CH₂)₂SH to form a dithiolane. The freed alcohol was then protected as its TBS ether and the same protecting group selectively removed from the primary alcohol to form 16. To avoid removing the dithiolane group at a later stage in the synthesis the thio-acetal was converted to the dimethyl acetal 17 using PhI(OCOCF₃)₂ and methanol.

The next stage in the synthesis was to extend 17 for the building of the triene region. The terminal alcohol was oxidised to its aldehyde using BaMnO₄ , then a Wittig reaction was carried out using Ph₃P=CHCO₂Et and CH₂Cl₂ to form the second double bond. Reduction of the ester group to an alcohol was carried out using DIBAL-H, then treatment with PPh₃ and exposure to the air gave rapamycin fragment 2.

Synthesis of C22-C42 fragment

Here the retro-synthesis of 3 is shown, giving the three synthetic precursors 5, 6 and 7

It was thought 4 could be obtained by alkylative coupling of a vinyllithium species generated from 7 to the Weinreb amide 6. The nucleophilic opening of epoxide 5 by the lithiated sulfone from phenyl sulfone 4 would then produce the desired fragment.

The ester 18 was used as a starting material to make fragment 6.

A Wittig reaction followed by reduction and protection steps produced 19. This was hydrogenated using a rhodium catalyst to give syn-dimethyl product 20. The minor anti diastereomer was successfully separated off. 20 was oxidised then underwent an aldol condensation to give adduct 21.

Transamination of 21 and protection of the alcohol with PMB resulted in amide 6, corresponding to the C₂₂-C₂₈ segment of rapamycin.

The vinyl bromide 7 was prepared using ester 22 as a starting material.

Reduction of 22 followed by dibromoolefination resulted in product 23. Acetylene 24 was prepared using n-BuLi, THF and MeI, then sulfenylation with Ph₂S₂ and bromination gave fragment 7.

Iodination and alkylation of starting material 25 with the lithiated allylic sulfide shown followed by a number of further steps resulted in its conversion to fragment 5.

Fragments 7 was first converted to its vinyllithium using t-BuLi then combined with 6 forming an enone in 78% yield. Stereoselective reduction of the carbonyl group using Zn(BH₄)₂ gave an alcohol which was protected with DEIPS giving 28. The phenyl sulfide was oxidised to a sulfone using m-CPBA in excess pyridine.

Lithiation and addition of the epoxide 5 resulted in the hydroxy sulfone in a 4:1 ratio of two diastereomers which were separated by HPLC. Metalation using n-BuLi followed by oxidation formed the total C₂₂-C₄₂ fragment.

Total synthesis of rapamycin through the combination of C₁₀-C₂₁ and C₂₂-C₄₂ fragments.

Fragment 3 (C₂₂-C₄₂) was treated with (S)-Boc-pipecolinal, followed by a Swern oxidation resulted in the aldehyde 29.

Condensation with the lithium salt of phosphine oxide 2 (C₁₀-C₂₁) produced the triene shown below.

The triene was hydrolysed with pyridinium p-toluenesulfonic acid and an aldol reaction was performed. Treatment with triethylsilyl triflate produced an amino acid which was subjected to Mukaiyama macrocyclization conditions to form the 31-membered ring. Finally, deprotection steps were performed to give synthetic rapamyin (1). This was judged to be identical to natural rapamycin by comparison of physical properties, ¹H-NMR, ¹³C-NMR, IR and UV spectral data.

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Synthesis

http://www.google.co.in/patents/US3929992

PREPARATION

CUT PASTE FROM TEXT

In one embodiment of this invention rapamycin is prepared in the followingmanner: 4

A suitable fermenter is charged with production meis reached in the fermentation mixture after 2-8 days,

usually after about 5 days, as determined by the cup plate method and Candida albicans as the test organism. The mycelium is harvested by filtration with diatomaceous earth. Rapamycin is then extracted from the mycelium with a water-miscible solvent, for example a lower alkanol, preferably methanol or ethanol. The latter extract is then concentrated, preferably under reduced pressure, and the resulting aqueous phase is extracted with a water-immiscible solvent. A preferred water-immiscible solvent for this purpose is methylene dichloride although chloroform, carbon tetrachloride, benzene, n-butanol and the like may also be used. The latter extract is concentrated, preferably under reduced pressure, to afford the crude product as an oil.

The product may be purified further by a variety of methods. Among the preferred methods of purification is to dissolve the crude product in a substantially nonpolar, first solvent, for example petroleum ether or hexane, and to treat the resulting solution with a suit able absorbent, for example charcoal or silica gel, so that the antibiotic becomes absorbed on the absorbant. The absorbant is then separated and washed or eluted with a second solvent more polar than the first solvent, for example ethyl acetate, methylene dichloride, or a mixture of methylene dichloride and ether (preferred). Thereafter, concentration of the wash solution or eluate affords substantially pure rapamycin. Further purification is obtained by partial precipitation with a nonpolar solvent, for example, petroleum ether, hexane, pentane and the like, from a solution of the rapamycin in a more polar solvent, for example, ether, ethyl acetate, benzene and the like. Still-further purification is obtained by column chromatography, preferably employing silica gel, and by crystallization of the rapamycin from ether.

In another preferred embodiment of this invention a first stage inoculum of S treptomyces hygroscopicus NRRL 5491 is prepared in small batches in a medium containing soybean flour, glucose, ammonium sulfate, and calcium carbonate incubated at about 25C at pH 7.l-7.3 for 24 hrs. with agitation, preferably on a gyrotary shaker. The growth thus obtained is used to inoculate a number of somewhat larger batches of the same medium as described above which are incubated at about 25C and pH 7.1-7.3 for 18 hrs. with agitation, preferably on a reciprocating’shaker, to obtain a sec- “ond stagc inoculum which is used to inoculate the production stage fermenters.

6 5.86′.2.-The fermenters are inoculated with the second stage inoculum described above and incubated at about 25C with’ agitationand aeration while controlling and ‘mai’ntaining the mixture at approximately pH 6.0 by

addition offa base, for example, sodium hydroxide, potassium hydroxide or preferably ammonium hydroxide, as required from time to time. Addition of a source -of assimilable carbon, preferably glucose, is started when theconcentrationof the latter in the broth has dropped to about 0.5% wt/vol, normally about 48 hrs after. the start of fermentation, and is maintained until the end ofthe particular run. In this manner a fermentation broth containing about 60 ug/ml of rapamycin as determined by the assay method described above is obtained in 45 days, when fermentation is stopped.

‘ Filtration of the’mycelium, mixing the latter with a watef-miscible ‘lower’ alkanol, preferably methanol, followed by extraction with a halogenated aliphatic hydrocarbon, preferably trichloroethane, and evaporation of the solvents yields a first oily residue. This first oily residue is dissolved in a lower aliphatic ketone, preferably acetone, filtered from insoluble impurities, the filtrate evaporated to yield a second oily residue which is extractedjwith a water-miscible lower alkanol,

preferably methanol, and the latter extract is evaporated to yield crude rapamycin as a third oily residue. This third oily residue is dissolved in a mixture of a lower aliphatic ketone and a lower aliphatic hydrocarbon, preferably acetone-hexane, an absorbent such as charcoal or preferably silica gel is added to adsorb the rapamycin, the latter is eluted from the adsorbate with a similar but more polar solvent mixture, for example a mixture as above but containing a higher proportion of the aliphatic ketone, the eluates are evaporated and the residue is crystallized from diethyl ether, to yield pure crystalline rapamycin. In this manner a total of 45-5 8% of the rapamycin initially present in the fermentation mixture is recovered as pure crystalline rapamycin.

CHARACTERIZATION solvent systems; for example, ether-hexane 40:60 (Rf 0.42), ‘isopropyl alcoholvbenzene 15:85 (Rf= 0.5) and ethanol-benzene 20:80 (Rf f 0.43);

d. rapamycin obtained from four successive fermentation batchesgave the following values on repeated The production stage fermenters are equipped with 7 devices for controlling and maintaining pH at a predetermined level and for continuous metered addition of elemental analyses:

AVER- e. rapamycin exhibits the following characteristic absorption maxima in its ultraviolet absorption spectrum ethanol):

f. the infrared absorption spectrum of rapamycin in chloroform is reproduced in FIG. 1 and shows characteristic absorption bands at 3560, 3430, 1730, 1705 and 1630-1610 cm;

Further infrared absorption bands are characterized by the following data given in reciprocal centimeters with (s) denoting a strong, (m) denoting a medium, and denoting a weak intensity band. This classification is arbitrarily selected in such a manner that a band is denoted as strong (s) if its peak absorption is more than two-thirds of the background in the same region; medium (m) if its peak is between one-third and twothirds of the background in the same region; and weak if its peak is less than one-third of the background in the same region.

2990 cm (m) 1158 cm” (m) 2955 cm (s) 1129 cm (s) 2919 cm (s) 1080 cm (s) 2858 cm (s) 1060 cm (s) 2815 cm (m) 1040 cm (m) 1440 cm (s) 1020 crn’ (m) 1365 cm (m) 978 cm” (s) 1316 cm (in) 905 cm (m) 1272 cm (m) 888 cm” 1178 cm (s) 866 cm- g. the nuclear magnetic resonance spectrum of rapamycinin deuterochloroform is reproduced in FIG. 2; SEE PATENT

CLAIMS

l. Rapamycin, an antibiotic which a. is a colourless, crystalline compound with a melting point of 183 to l8SC, after recrystallization from ether;

b. is soluble in ether, chloroform, acetone, methanol and dimethylformamide, very sparingly soluble in hexane and petroleum ether and substantially insoluble in water;

c. shows a uniform spot on thin layer plates of silica gel”,

d. has a characteristic elemental analysis of about C,

e. exhibits the following characteristic absorption maxima in its ultraviolet absorption spectrum (95% ff has ‘a characteristic infrared absorption spectrum shown in accompanying FIG. 1; SEE PATENT

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Rapamycin synthetic studies. 1. Construction of the C(27)-C(42) subunit. Tetrahedron Lett 1994, 35, 28, 4907

A partial synthesis of rapamycin has been reported: The condensation of sulfone (I) with epoxide (II) by means of butyllithium followed by desulfonation with Na/Hg gives the partially protected diol (III), which is treated with methanesulfonyl chloride and NaH to afford the epoxide (IV). Ring opening of epoxide (IV) with LiI and BF3.Et2O followed by protection of the resulting alcohol with PMBOC(NH)CCl3 yields the primary iodo compound (V). The condensation of (V) with the fully protected dihydroxyaldehyde (VI) (see later) by means of butyllithium in THF/HMPT gives the fully protected trihydroxyketone (VII), which is hydrolyzed with camphorsulfonic acid (CSA) to the corresponding gemdiol and reprotected with pivaloyl chloride (the primary alcohol) and tert-butyldimethylsilyl trifluoromethanesulfonate (the secondary alcohol), yielding a new fully protected trihydroxyketone (VIII). Elimination of the pivaloyl group with DIBAL and the dithiane group with MeI/CaCO3 affords the hydroxyketone (IX), which is finally oxidized with oxalyl chloride to the ketoaldehyde (X), the C(27)-C(42) fragment [the C(12)-C(15) fragment with the C(12)-substituent based on the IUPAC nomenclature recommendations]. The fully protected dihydroxyaldehyde (VI) is obtained as follows: The reaction of methyl 3-hydroxy-2(R)-methylpropionate (XI) with BPSCl followed by reduction with LiBH4 to the corresponding alcohol and oxidation with oxalyl chloride gives the aldehyde (XII), which is protected with propane-1,3-dithiol and BF3.Et2O to afford the dithiane compound (XIII). Elimination of the silyl group with TBAF followed by esterification with tosyl chloride, reaction with NaI and, finally, with sodium phenylsulfinate gives the sulfone (XIV), which is condensed with the partially protected dihydroxyaldehyde (XV), oxidized with oxalyl chloride and desulfonated with Al/Hg to afford the dithianyl ketone (XVI). The reaction of (XVI) with lithium hexamethyldisilylazane gives the corresponding enolate, which is treated with dimethyllithium cuprate to yield the fully protected unsaturated dihydroxyaldehyde (VI).

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http://www.google.com/patents/US8088789

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Total Synthesis of Rapamycin

Volume 46, Issue 4, pages 591–597, January 15, 2007

PREVIEW THIS ARTICLE WITH READCUBE

http://www.readcube.com/articles/10.1002%2Fanie.200604053?r3_referer=wol

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Ley, Maddess, Tackett, Watanabe, Brennan, Spilling, Scott and Osborn. ACIEE, 2006, EarlyView. DOI:10.1002/anie.200604053.

It’s been in the works for quite a while, but Steve Ley’s synthesis of Rapamycin has just been published. This complex beast has a multitude of biological activities, including an interesting immunosuppressive profile, resulting in clinical usage following organ transplantation. So, unsurprisingly, it’s been the target of many projects, with complete total syntheses published by Smith, Danishefsky, Schreiber and KCN.

So what makes this one different? Well, it does have one of the most interesting macrocyclisations I’ve seen since Jamison’s paper, and a very nice demonstration of the BDA-aldol methodology. The overall strategy is also impressive, so on with the retro:

First stop is the BDA-aldol; this type of chemistry is interesting, because the protecting group for the diol is also the stereo-directing group. The stereochemistry for this comes from a glycolic acid, and has been usedin this manner by the group before. The result is as impressive as ever, with a high yield, and presumably a very high d.r. (no mention of actual numbers).

The rest of the fragment synthesis was completed in a succinct and competent manner, but using relatively well known chemistry. However, I was especially impressed with the macrocyclisation I mentioned:

Tethering the free ends of the linear precursor with a simple etherification/esterification onto catechol gave then a macrocycle holding the desired reaction centres together. Treatment of this with base then induces a Dieckmann-condensation type cyclisation to deliver the desired macrocycle. Of course, at this stage, only a few more steps were required to complete the molecule, and end an era of the Wiffen Lab.

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Drugs Fut 1999, 24(1): 22

DOI: 10.1358/dof.1999.024.01.474036

In CDCl₃ rapamycin exists as a mixture of conformers in a 3:1 ratio, which complicates the NMR spectrum. In the table below the chemical shifts of the carbons and hydrogens of the major isomer only are given.

REFERENCES

3. Creating diverse target-binding surfaces on FKBP12: synthesis and evaluation of a rapamycin analogue library.

4. Mammalian target of rapamycin: discovery of rapamycin reveals a signaling pathway important for normal and cancer cell growth.

5. Hybrid inhibitors of phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR): design, synthesis, and superior antitumor activity of novel wortmannin-rapamycin conjugates.

6. Fluorescent probes to characterise FK506-binding proteins.

7. Recent advances in the chemistry, biosynthesis and pharmacology of rapamycin analogs.

8 Total synthesis of rapamycin.

9  Highly diastereoselective desymmetrisation of cyclic meso-anhydrides and derivatisation for use in natural product synthesis.

10  Total synthesis studies on macrocyclic pipecolic acid natural products: FK506, the antascomicins and rapamycin.

11 Determination of sirolimus in rabbit arteries using liquid chromatography separation and tandem mass spectrometric detection.

12  Saccharomyces cerevisiae FKBP12 binds Arabidopsis thaliana TOR and its expression in plants leads to rapamycin susceptibility.

13 Total synthesis of rapamycin.

14 Drug evaluation: AP-23573–an mTOR inhibitor for the treatment of cancer.

16 CCI-779 Wyeth.

17 Everolimus. Novartis.