Total synthesis of a 28-member stereoisomer library of murisolins

Total syntheses of two 16-member libraries of murisolin isomers are reported. In the first library, fluorous PMB (p-methoxybenzyl) groups encode configurations, and four mixtures of four dihydroxy-tetrahydrofurans are prepared by Shi epoxidation followed (optionally) by Mitsunobu reaction. The mixtures are coupled by Kocienski-Julia reaction with a single hydroxybutenolide followed by hydrogenation. Demixing and detagging provide the 16 pure stereoisomers. In the second synthesis, a single mixture of four fluorous-tagged dihydroxy-tetrahydrofurans is coupled with a four-compound mixture of hydroxybutenolides that bear derivatives of DMB (dimethoxybenzyl) groups with oligoethylene glycol (OEG) units that encode the configurations at C4 and C34. The 16-compound mixture is subjected to hydrogenation, double demixing, and detagging to provide the 16 isomerically pure murisolins. Twelve of these isomers are new, while four match samples from the first library.     

The azido acid approach to β-peptides: parallel synthesis of a tri-β-peptide library by fluorous tagging

A small tri-β-peptide library was prepared starting from three enantio- and diastereopure azido acids. Fluorous tagging followed by two cycles of azide reduction, fluorous solid phase extraction (f-SPE), peptide coupling with the original azido acids, and f-SPE provided 27 protected azido peptides. Reduction and HPLC purification provided 25 of the 27 targeted tri-β-peptides in acceptable yields and excellent purities.     

Quasiracemic synthesis: concepts and implementation with a fluorous tagging strategy to make both enantiomers of pyridovericin and mappicine

The concept of quasiracemic synthesis is introduced and illustrated with syntheses of both enantiomers of pyridovericin (whose absolute configuration is assigned as R) and mappicine. Like racemic synthesis, quasiracemic synthesis provides both enantiomers in a single synthetic sequence; however, separation tagging is used to ensure that quasiracemic mixtures can be analyzed, separated, and identified on demand. Fluorous tags of differing chain lengths are used to tag two enantiomeric starting materials. The resulting quasienantiomers are mixed to make a quasiracemate, which is then treated like a true racemate in successive steps of the synthesis. Fluorous chromatography is used to separate, or demix, the final quasiracemate into its two components, which are then detagged to provide (true) enantiomeric products. Quasiracemic synthesis is portrayed as the first and simplest of a series of mixture synthesis techniques based on separation tagging, and the prospects for using other types of separation tags are briefly evaluated.     

A fluorous, Pummerer cyclative-capture strategy for the synthesis of N-heterocycles

A fluorous, cyclative-capture strategy based on a new Pummerer cyclization process allows rapid access to tagged, heterocyclic frameworks. Convenient modification of the fluorous, heterocyclic scaffolds by using a variety of approaches including Pd-catalyzed cross-couplings is possible. Traceless, reductive cleavage of the fluorous-phase tag or oxidative cleavage and further elaboration, completes a strategy for the high-throughput, fluorous-phase synthesis of a diverse range of N-heterocycles.     

FluoMar,a fluorous version of the Marshall resin for solution-phase library synthesis

[structure: see text] The fluorous counterpart of the Marshall resin, 4-(1H,1H,2H,2H-perfluorodecylsulfanyl)phenol (FluoMar), is prepared by S-alkylation of 4-mercaptophenol with C(8)F(17)CH(2)CH(2)I and employed in the synthesis of amide and diamide analogues. The final products are purified by solid-phase extraction (SPE) over FluoroFlash silica cartridges.     

Solution-phase parallel synthesis of an N-alkylated dihydropteridinone library from fluorous amino acids

Parallel synthesis of an N-alkylated dihydropteridinone library has been accomplished in five steps starting from two displacement reactions of 4,6-dichloro-5-nitropyrimidine, first with fluorous amino acids, then with secondary amines. The hydrogenation of the nitro group followed by microwave-assisted cyclization gave the dihydropteridinones. Further diversification was achieved by the reaction of dihydropteridinones with benzyl halides to afford mono-N-alkylated products. All the reaction intermediates and final products were purified by SPE or precipitation without the need to perform chromatography.     

Enantioselective synthesis of macrolactone core of the natural product Sch725674

An enantioselective synthesis of the macrolactone core of natural product Sch725674 was accomplished from furfural. Key reactions in assembly of the macrolactone are the use of furan as a but-2-ene-dione equivalent and ring closing metathesis.     

A convenient method for the preparation of fluorous tin derivatives for the fluorous labeling strategy

A convenient method for the preparation of fluorous aryl stannanes was developed as a means of expanding the general utility of the fluorous labeling strategy (FLS). Following the synthesis of a novel fluorous distannane, a palladium-catalyzed cross-coupling reaction was used to prepare the target compounds from aryl halides. The scope of the reaction was investigated by preparing a small library of model compounds where the reaction yields were similar to those reported for the analogous procedures employing hexamethyl- or hexabutyldistannanes. The utility of the reported methodology was demonstrated through the successful synthesis of fluorous precursors to two established molecular imaging and therapy agents (FIAU, IUdR). These were radiolabeled with iodine-125 and the desired products isolated in high yield and effective specific activity.     

Solution-phase preparation of a 560-compound library of individual pure mappicine analogues by fluorous mixture synthesis

Solution-phase mixture synthesis has efficiency advantages and favorable reaction kinetics. Applications of this technique, however, have been discouraged by the difficulty in obtaining individual, pure final products by using conventional separation and identification processes. Introduced here is a new strategy for mixture synthesis that addresses the separation and identification problems. Members of a series of organic substrates are paired with a series of fluorous tags of different chain lengths. The tagged starting materials are then mixed and taken through a multistep reaction process. Fluorous chromatography is used to demix the tagged product mixtures on the basis of the fluorine content of the tags to provide the individual pure components of the mixture, which are detagged to release the final products. The utility of fluorous mixture synthesis is demonstrated by the preparation of a 560-membered library of analogues of the natural product mappicine. A seven-component mixture is carried through a four-step mixture synthesis (two one-pot and two parallel steps) to incorporate two additional points of diversity onto the tetracyclic core. Methods for analysis and purification of the intermediates are established for the quality control of the mixture synthesis.     

A bidirectional approach to the synthesis of a complete library of adjacent-bis-THF annonaceous acetogenins

Thirty-six stereoisomers of bifunctional adjacent bis-THF (tetrahydrofuran) lactones have been synthesized, which can afford a complete library of the adjacent bis-THF Annonaceous acetogenins. The bis-THF lactones were synthesized, starting from the enantioselectively pure 8,9:12,13-(E,E and Z,E)-16-benzyloxy-5-hydroxy-hexadeca-1,4-olide, in a highly distereoselective manner using oxidative reactions, including rhenium(VII) oxides-mediated oxidative cyclization, Shi's asymmetric epoxidation, and Sharpless asymmetric dihydroxylation reactions. Using the nonsymmetrical bis-THF lactones, syntheses of two nonnatural acetogenins were achieved.     

Noncovalent fluorous interactions for the synthesis of carbohydrate microarrays

A surface patterning method based on noncovalent immobilization of fluorous-tagged sugars on fluorous-derivatized glass slides allows the facile fabrication of carbohydrate microarrays. To expand the scope of these arrays, the first syntheses are reported of arabinose, rhamnose, lactose, maltose, and glucosamine tagged with a single C₈F₁₇-tail for ease of purification as well as array formation. Screening of these carbohydrate microarrays against lectins from Triticum vulgaris (WGA) and Arachis hypogaea (PNA) demonstrate that the noncovalent fluorous–fluorous interaction is sufficient to retain not only mono- but also disaccharides under the biological assay conditions.     

Fluorous mixture synthesis of fused-tricyclic hydantoins. Use of a redundant tagging strategy on fluorinated substrates

Simple HPLC experiments were used to identify a redundant tagging scheme wherein six different amino acids were tagged with only four fluorous tags. The tagged amino acids were converted to regiosiomeric mixtures of tricyclic hydantoins. Despite the lack of selectivity, the mixtures were demixed and detagged to give 11 individual pure products in just 25 steps.     

Enantioselective synthesis of each stereoisomer of the pyranoid linalool oxides: the linalool route

Each of the four enantiomerically pure tetrahydropyran linalool oxides was prepared by separate enantioselective Sharpless dihydroxylation of (R)- or (S)-linalyl acetate with AD-mix-α or AD-mix-β, followed by a completely stereoselective N-phenylselenophthalimide cyclization of an intermediate allylic alcohol.     

Enantioselective synthesis of each stereoisomer of the pyranoid linalool oxides: the geraniol route

Each of the four enantiomerically pure tetrahydropyran linalool oxides was synthesized by an acid-catalyzed cyclization of an appropriate epoxy-alcohol obtained by consecutive Sharpless dihydroxylation (AD) and epoxidation (AE) reactions of geraniol derivatives. An interesting example of double asymmetric induction was observed during the AE of a bis(homoallylic) N-naphthylcarbamate.     

Synthesis of fluorous trialkyl phosphines with the complete exclusion of PH3

A novel synthetic protocol has been developed for the synthesis of fluorous tertiary phosphines excluding the use of hazardous PH₃ and with control over the number of methylene spacers and the length of fluorous ponytails.