Monosaccharides and Analogues from Simple Achiral Unsaturated Compounds

Glycochemistry today CHIMIA 2011, 65, No. 1/2 91 doi:10.2533/chimia.2011.91 Chimia 65 (2011) 91–96 © Schweizerische Chemische Gesellschaft *Correspondence: Dr. A. J. Moreno-Vargas Department of Organic Chemistry Faculty of Chemistry University of Seville Prof. Garcia González, 1, Seville, Spain E-mail: [email protected] Monosaccharides and Analogues from Simple Achiral Unsaturated Compounds Antonio J. Moreno-Vargas*, Ana T. Carmona, Elena Moreno-Clavijo, and Inmaculada Robina Abstract: We present herein a selection of ingenious methods that have been developed to convert inexpensive furan, pyrrole and unsaturated hydrocarbons into enantiomerically enriched monosaccharides and analogues of biological interest. Keywords: Cycloadditions · Furan · Iminoalditols · Monosaccharides· Polyenes · Pyrrole 1. Cycloadditions of Furans and Pyrroles The synthesis of carbohydrates and analogues from 7-oxabicyclo[2.2.1]hept-2enes as starting materials was pioneered by Just[1] and developed extensively by Vogel’s group. 1-Cyanovinyl (1’S)-camphanate adds to furan in the presence of ZnI2 as catalyst to give a mixture of diastereomeric Diels-Alder adducts, from which adduct 1 can be isolated pure by crystallization. Starting from (1R)-camphanic acid, large quantities of pure adduct 2 were prepared.[2] Enantiomerically pure 7-oxanorbornenyl derivatives 1 and 2 and their products of saponification, ketones (+)-3 and (–)-3, are named ‘naked sugars’ as they are chirons like those derived from natural hexoses. They are also homochirallike sugars but with three unsubstituted (naked) carbon centers. Their substitution following highly stereoselective methods gives polysubstituted 7-oxabicyclo[2.2.1] heptane-2-ones that can be regioselectively oxidized into different uronolactones 4, 5 and 6 which are precursors of d-ribose derivative 7, d-allose and l-talose.[3] Starting from 2, l-allose and d-talose were also similarly prepared[4] (Scheme 1). The ‘naked sugar’ methodology has been also used for the synthesis of deoxypolyoxin C (Scheme 2). The a-bromouronolactone (–)-6 gives an allyl uronic ester on treatment with allyl alcohol and triflic acid that was converted into azidoderivative 8. Compound 8 could be transformed into deoxypolyoxin C.[5] It also permitted the first synthesis of (+)-d-allonojirimycin (Scheme 2).[6] l-Daunosamine[7] was also obtained from chiron 1.[8] The ‘naked sugars’ have been converted into long-chain sugars and C-disaccharides,[9] castanospermine and derivatives,[10] and to the OCN OR* 1R* = (1'S)-camphanoyl 2R* = (1'R)-camphanoyl O O OCN OR O O OO O O OO O 11. H2O2, OsO4 2. (MeO)2CMe2 TsOH 1. KOH, H2O THF 2. CH2O/H2O mCPBA O O O OMeHO (-)-4 (-)-7 O O (-)-3 (+)-3 O O O O O OR 5 O OH OH OH HO HO (L-allose ← ← 2) D-allose O O O O O Br 6 O OH OH OH OH HO (D-talose ← ← 2) L-talose saponification Scheme 1. Use of ‘first-generation naked sugars’. O O O COO Br O O O O COOBn N3O OH 1. Rh(PPh3)3Cl EtOH/H2O DABCO 2. CsN3 3. BnBr (-)-6 8 O HOOC H2N HO OH N NH O O deoxypolyoxin C NH 2 Cl HO OH HO OH HO 1. LiAlH4 2. HCl (+)-D-allonojirimycin hydrochloride TfOH Scheme 2 Scheme 2. Total synthesis of deoxypolyoxin C and of (+)-d-allonojirimycin. 92 CHIMIA 2011, 65, No. 1/2 Glycochemistry today Other enantiomerically pure 7-azabicyclo[2.2.1]heptane analogues, such as compounds (–)-15, (+)-16[18] and (+)-17[19] and their corresponding enantiomers, were also reported by Vogel’s group (Scheme 5). Compounds (–)-15 and (+)-16 and their corresponding enantiomers were successfully transformed into the iminosugar 18 and its enantiomer, respectively, which first examples of polyhydroxylated indolizidines[11] and quinolizidines.[12] Hoffmann and co-workers have developed the synthesis of homochiral 2,6-anhydroheptitols from 8-oxabicyclo[3.2.1] octan-3-one.[13] Enantiomerically pure 3-oxo-8-oxabicyclo[3.2.1]octyl-2-yl derivatives were obtained by [4+3] addition of furan with chiral 1,2-dioxyallyl cation engendered in situ by acid-catalyzed heterolysis of enantiomerically pure mixed acetals derived from 1,1-dimethoxyacetone and enantiomerically pure secondary benzyl alcohols.[14] Adduct (–)-9 was obtained in this manner. This compound was enolized regioselectively and oxidized with mCPBA giving, after esterification, pivalate 10 that was easily converted into anhydroheptitol 11 (Scheme 3). Vogel and co-workers have also extended the ‘naked sugar’ methodology to the synthesis of further products of interest, such as dideoxyiminoalditols and polyhydroxylated prolines (‘aza naked sugar’ methodology). The synthesis of the aza-analogue of compound 3, 7-azabicyclo[2.2.1]hept-5-en-2-one 12, was reported in 1999[15] by Trudell et al. in the racemic form, starting from N-Boc-pyrrole and 2-bromethynyl p-tolyl sulfone. This synthesis was later improved[16] (Scheme 4). The enantiomerically pure forms of 12 were recently reported.[17] OMe O OMe + HO Ph Me O Ph O OMe O Ph OTES OMe (i-Pr) 2 NLi, Et 3 SiCl Et 3 N, THF, -78°C O O O O Ph H O O O Ph H OPiv -95°C Me 3 SiOTf 1. (i-Pr) 2 NLi, Et 3 SiCl Et 3 N, THF 2. mCPBA, THF, H 2 O 3. PivCl, Et 3 N, DMAP, CH 2 Cl 2 (-)-9 10 O HO OTBS OPiv HO 11 OH Scheme 3 Scheme 3. Hoffmann’s asymmetric [4+3]cycloaddition of furan: total synthesis of 2,6-anhydroheptitols. Scheme 4. Synthesis of enantiomerically pure 7-azabicyclo[2.2.1] heptan-2-ones. Boc N O Boc N O Ts N Boc Br Ts (±)-12 + SmI2 THF, -78 °C 75% ref. [16] Boc NBoc N O (+)-12 Boc N N N H H Ph Ph N N H H Ph Ph 42% Boc N O (-)-12 H2N H2N Ph Ph (R,R)-14 1. (R,R)-14, CH2Cl2 4Åmol. sieves 2. Flash chromatography H3PO4(0.1 M)-THF 43% 95% 96% ref. [17] (±)-13 Boc N O rac-12 Boc N (-)-15 O O Boc N O (+)-17 O O (±)-13 N3 Ts Boc N O O N3 Ts + (+)-16 Boc N O ON Bu3SnH/AIBN Toluene, reflux 56% H2 N OHHO H3N OH Cl Cl 18.(HCl)2 Boc N OO HO COOH 1. H2, Pd-C MeOH 2. HCl-THF quant. ref [21] ref [19] Boc N OTBS O O 1. O3, MeOH 2. NaBH4 CF3CON(Me)TBS Et3N, DMF 86% 88% (-)-19 Boc N O PhSe Cl Boc N OH Cl (4 steps, including racemic resolution) 1. O3, MeOH 2. Me2S PhSeCl CHCl3, -78 ºC 75% Boc N OR* R* = camphanoyl (2 steps) Boc N + OR* Boc N Cl OH 1. O3, MeOH 2. Me2S rac-21 Boc N MeO COOMe OMe OH (-)-20 (3 steps including addition of PhSeCl) Boc N MeO COOMe MeO OH Scheme 5. 7-Azabicycloheptanes as intermediates for the synthesis of dideoxyiminosugars and hydroxylated proline derivatives. Glycochemistry today CHIMIA 2011, 65, No. 1/2 93 epoxide 35 which can be converted into 1,4-dideoxy-1,4-imino-d-lyxitol 36 (Scheme 10).[35] Similarly, Schreiber and co-workers[36] have obtained (+)-KDO from the diallyl alcohol 37 (Scheme 11). 4. Kinetic Resolution of Racemic Allylic Alcohols The Katsuki-Sharpless asymmetric epoxidation of racemic diol (±)-38 gave, after chromatographic separation, the erythro-epoxide (+)-39 which was further transformed into d-olivose (Scheme 12). Asymmetric epoxidation of the kinetically resolved dienol (–)-40 gave the corshowed strong competitive inhibition towards a-mannosidases.[20] The key step of this transformation implies a novel rearrangement on the bicyclic system through aminyl radicals.[21] Ketones 17 and 12 were transformed into polyhydroxylated proline derivatives 19,[19] 20 and 21,[22] following the same methodology that was previously employed in the case of oxa-analogues (‘naked sugar’ chemistry[8a]). These prolines are expected to be useful intermediates for the preparation of new dideoxyiminosugars, such as polyhydroxylated indolizidines and pyrrolizidines, in the search for new glycosidase inhibitors. 2. Carbohydrates and Analogues from Achiral Polyenes An elegant total synthesis of acosamine and of daunosamine was developed at Roche starting from cyclopentadiene.[23] Monomethylation of cyclopentadiene gives 5-methylcyclopentadiene that is hydroborinated asymmetrically with (–)-di3-pinanylborane giving (S)-alcohol 22. Epoxidation syn with respect to the homoallylic alcohol provides 23, which is oxidized into ketone 24. Baeyer-Villiger oxidation of 24 is regioselective and leads to lactone 25. This compound was then transformed into methyl-a-acosaminide and daunosamine⋅HCl (Scheme 6). Johnson and co-workers reported a total synthesis of 1,3-dideoxynojirimycin starting from cyclopentadiene.[24] Photooxidation of cyclopentadiene and reductive work-up with thiourea generates ciscyclopent-2-ene-1,4-diol. Its enzymatic enantioselective monoacylation, silylation and subsequent treatment with KOH and oxidation, gave enantiomerically pure enone 26[25] which was transformed into 27 and (+)-28 as depicted in Scheme 7. A similar approach converted enantiomerically pure (2R,3R)-2,3-isopropylidenedioxycyclopent-4-en-1-one derived from cyclopentadiene[26] into (–)-1-deoxymannonojirimycin and (–)-1-deoxytalonojirimycin (1,5-dideoxy-1,5-imino-d-talitol).[27] Enone 26 was converted to (2R,3S)-2,3bis[(tert-butyl)dimethylsilyloxy]cyclopent-4-en-1-one and then to (+)-1-deoxynojirimycin.[28] Dioxygenases, present in the blocked mutants of the soil bacterium Pseudomonas putida, degrades benzene and its derivatives into cyclohexa-3,5-diene-1,2-diols. With chlorobenzene, diol 29 is obtained with >99% ee. This compound is converted in a few chemical steps into several sugars and derivatives[29] such as l-erythrose, KDN,[30] (–)-Neu-5-Ac[31] and Vitamin C[32] (Scheme 8). When applied to penta-1,4-diene, the Sharpless asymmetric dihydroxylation forms a 1:1 mixture of (2S,4S)- and (2S,4R)-penta-1,2,4,5-tetrols, 30 and 31 (Scheme 9), which can be converted to diepoxides 32 and 33, respectively.[33] The former was converted into dideoxypentitol and -thiopentitol. A stereoand enantioselective synthesis of 32 is possible starting from 1,5-dichloropenta-2,4-diene applying Noyori’s asymmetric hydrogenation.[34] 3. Desymmetrization of meso Dienols Katsuki-Sharpless desymmetrization of penta-1,4-dien-3-ol (34) gives the monoMe Me HO Me HO O MeI 0°C mCPBA NaHCO3 1. 2. H2O2/NaOH )2BH CrO3 py 22 23 Me O O O O O Me mCPBA NaHCO3 CH2Cl2 O OMe Me OH NH2 methyl α-acosaminide daunosamine⋅HCl 24 25 Na O OH Me OH NH2 .HCl Scheme 6. Roche’s synthesis of a-acosamine and daunosamine. NH HO HO HO O RO OR RO OR 1. I 2 , py, CCl 4 2. NaBH 4 , CeCl 3 , MeOH 3. TBSCl, imidazole 4. CO, Bu 3 SnH, Pd(PPh 3 ) 4 5. NaBH 4 ⋅CeCl 3 , MeOH 6. TBSCl, imidazole 1. O 3 , MeOH, -78 o C 2. Me 2 S, 20 o C 3. BnNH 3 Cl Na(CN)BH 3 4. HCl, MeOH 5. H 2 , Pd-C 26 27 (+)-28 R = TBS = SiMe 2 (t-Bu) Scheme 7 Scheme 7. Johnson’s synthesis of 1,3-dideoxynojirimycin. Cl Cl OH OH Cl O O Pseudomonas putida 39D (MeO)2CMe2 TsOH 29 OO OOH L -erythrose acetonide D -erythrose acetonide O O O HO O O O O L -ribonic-γ-lactone acetonide HO O O O O HO HO H O HO F OH OH HO 2-fluoroD -glucose O HO HO OH OH OH OH COOH KDN O HO OH OH OH OH COOH AcNH (-)-Neu5Ac OH OH O O H HO OH Vitamin C D -mannonic-γlactone acetonide Scheme 8 Scheme 8. Hudlicky’s syntheses of tetrose, pentose and hexose derivatives and Banwell’s syntheses of KDN, Neu5Ac and Vitamin C. 94 CHIMIA 2011, 65, No. 1/2 Glycochemistry today responding epoxide (75%) that could be transformed into d-digitoxose.[37] In a similar manner (+)-oliose, (+)-cymarose,[38] dand l-chalcose[39] were also prepared. Application of the Katsuki-Sharpless enantioselective epoxidation to racemic monoO-benzylated divinylglycol allowed the preparation of enantiomerically pure l-lyxo and d-lyxo-pentoses and analogues.[40] 5. Enantioselective Sharpless Dihydroxylation and Aminohydroxylation This is an extremely powerful method for the synthesis of monosaccharides and selected examples of application are collected in this section. For instance, tetritol and tetrose derivatives are obtained readily from asymmetric dihydroxylation of (E)- but-2-ene-1,4-diol,[41] and 4-deoxy dand l-threose are derived from benzene-1,2dimethyl acetal of (E)-crotonaldehyde. In a similar way, 2-deoxyxylofuranosides are obtained from 5-[(tert-butyldiphenylsilyl) oxy]-(E)-pent-3-enal.[42] Asymmetric dihydroxylation of 2-vinylfuran (41) gives diol (+)-42, which after oxidation with m-chloroperbenzoic acid and water elimination furnished (+)-isolevoglucosenone (Scheme 13). This compound can be isomerized into (–)-levoglucosenone. The lhexose derivative (–)-isolevoglucosenone is obtained with the same ease.[43] Starting from furfural and by applying the same route, dand l-mannose, dand l-gulose, dand l-talose[44] and 2-deoxy and 2,3-dideoxyhexoses[45] were obtained. The Sharpless asymmetric aminohydroxylation[46] of 2-vinylfuran 43 gives aminoalcohol 44, that was converted into the b-hydroxyfurylamine derivative 45,[47] useful building block for the synthesis of various biologically important compounds, including 1,5-dideoxy-1,5-iminoalditols (Scheme 14). A less regioselective, but shorter way to 45 is the direct asymmetric aminohydroxylation of vinylfuran. Sharpless asymmetric dihydroxylation of ethyl sorbate gives diol 46 regioand stereoselectively. This compound was transformed in several steps into tosylamide 47 which is then converted into methyl N-tosyl-a-d-tolyposaminide (–)-48. Alternatively, diol 46 is reacted with TsN=C=O to give 49. Hydrogenation of the alkene moiety and subsequent methanolysis and acidic treatment provides lactone 50, which was successfully transformed into 4-epi-N-tosyl-a-d-tolyposaminide (+)-51 (Scheme 15).[48] Lindström and co-workers[49] have also presented an efficient synthesis of five-membered iminoalditols in water that includes asymmetric dihydroxylation and epoxidation steps (Scheme 16). HO OH OH OH HO OH OH OH AD-mix-α (78%) + 30 31 1. TsCl, Py 2. NaH, THF O O O O OCuO ClCl 32 33 {[(R)-BINAP]RuCl2}2 Et3N, 120oC 1200 psi H2 MeOH OH OH ClCl OOH HO SOH OH S HO OH + KOH, Et2O (89%) NaOH, H2O 25oC, 36 h (78%) Na2S, EtOH 0oC, 7 h 5:1 (54%) (R)-BINAP: (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl Scheme 9. Conversion of penta-1,4-diene into pentitol derivatives. OH OH O OHNH2 OH N HO OH Ts Br 1. TsCl, py 2. NBS 34 (+)-AE N HO OH HOH 36 35 NH 3 Scheme 10 Scheme 10. Jäger’s synthesis of 1,4-dideoxy-1,4-iminopentitols. OBn OBn OH OBn OBn OH O (-)-AE (94%) 37 O HOOC OH HO OH OH OH (+)-KDO Scheme 11 Scheme 11. Schreiber’s total synthesis of (+)-KDO. O HO OH Me OH OH OH O OH + (-)-AE' (±)-38 (+)-39 O O O HO (-)-40 1. PhNCO, Py 2. BF3⋅Et2O1. H3O+ 2. O3 3. Me2S (+)-D-olivose (33% yield, >95% e.e. (+)-AE' O HO OH Me OH OH O1. H3O+ 2. O3 3. Me2S (+)-D-digitoxose (75% yield, 95% e.e.) Scheme 12. Total syntheses of 2,6-dideoxyhexoses. OO OH HO O O OH OH O O O mCPBA CH 2 Cl 2 TsOH PhH, 80°C AD-mix-α MeSO 2 NH 2 aq. t-BuOH 0°C (+)-42 (+)-isolevoglucosenone 41 OO O (-)-levoglucosenone Scheme 13 Scheme 13. Total synthesis of (+)-isolevoglucosenone and (–)-levoglucosenone. Glycochemistry today CHIMIA 2011, 65, No. 1/2 95 OOEt O O COOEt CbzN OH H 44 O CbzN OTBS H N O Cbz HO OTBS 45 Sharpless aminohydroxylation aza-Achmatowicz reaction (41%, e.e.>86%) 43 Scheme 14 Scheme 14. Application of the Sharpless asymmetric aminohydroxylation and of the aza-Achmatowicz reaction to the synthesis of iminosugars. 6. Birch Reduction of Pyrroles The Birch reduction of pyrroles with ester functionality at either C(2) or at both C(2) and C(5) is a useful method for the synthesis of iminosugar derivatives that has been broadly exploited by Donohoe’s group.[50] N-Boc pyrrole was doubly lithiCOOEt COOEt OH OH AD-mix-α CH 3 SO 2 NH 2 t-BuOH/H 2 O 46 (93% ee) COOEt OTBS NHTs 47 1. CF 3 COOH, THF/H 2 O, 20°C 2. (i-Bu) 2 AlH, THF/acetone, -78°C 3. TsOH/py (MeO) 3 CH/MeOH (-)-48 O TsHN Me OMe TsN=C=O Pd(Ph 3 P) 4 THF O NTs COOEt O 49 O O NHTs O TsHN Me OMe 1. H 2 /Pd-C, EtOAc, 20°C 2. NaOH/MeOH 3. CF 3 COOH/THF 50 1. (i-Bu) 2 AlH, THF/toluene, -78°C 2. TsOH/py, (MeO) 3 CH, MeOH (+)-51 94% 72% 86% 86% Scheme 15 Scheme 15. Synthesis of tolyposaminide derivatives. Br Br Br Br OH OH Br OH OH OH AD-mix-α, NaHCO 3 MeSO 2 NH 2 H 2 O/t-BuOH 1:1 0°C, 16 h (70%, 97% ee) H 2 O 50°C, 3 h (98%) Br OH OH OH H 2 O 2 (1.2 equiv.) H 2 O, 20°C K 2 [W 2 O 3 (O 2 ) 4 (H 2 O) 2 ] (0.02 equiv.) (99%, dr 96:4) O 10% NH 3 /H 2 O 4 h (88%) N OH OH HH HO OH Scheme 16 Scheme 16. Efficient asymmetric synthesis of an azasugar in water. N Boc LiTMP, MeOCOCI 78 ºCN Boc COOMe MeOOC N Boc COOMe MeOOC N Boc COOMe MeOOC 80% 10:1 cis 6:1 trans Li, NH3, THF, then NH4Cl Li, cat. DBB, THF, then 2,6-di-tertbutylphenol 80% N H HO OH OH HO N H HO OH OH HO DMDP N HO OH OH H HO (-)-2,3-7-triepiaustraline 52 53 53 54 Scheme 17. Partial reduction of pyrrole for the synthesis of DMDP and other iminosugars. ated with lithium 2,2,6,6-tetramethylpiperidide (LiTMP), followed by a quench with methyl chloroformate, to give diester 52 (Scheme 17). Pyrrole 52 can be reduced to give the trans isomer of 53 with good diastereoselectivity, using lithium in ammonia and quenching with ammonium chloride. Reduction under ‘ammonia-free’ conditions (Li, catalytic DBB, THF) followed by protonation with 2,6-di-tertbutylphenol gives cis-53 exclusively. These two pyrrolines were successfully transformed (among others) into the natural pyrrolizidine alkaloid (–)-2,3,7-triepiaustraline,[51] into the polyhydroxylated pyrrolidine 54 and into the natural glycosidase inhibitor DMDP.[52] 7. Conclusion For many years carbohydrates were very difficult synthetic targets because of their complexity arising from their stereochemistry and their multifunctional character. In parallel with the recent revolution in organic synthesis, a large number of complicated and rare monosaccharides have been prepared by total asymmetric synthesis starting from inexpensive and ready available starting materials, including furans recovered from the left-overs of agriculture (biomass) and pyrroles. Methods are available that allow one to reach both enantiomers of any natural or non-natural monosaccharide, including deoxyaminosugars, thiosugars and iminosugars, and this, quite often, in few synthetic steps. Depending on the target, pure chemical procedures can be applied successfully, alone or in combination with chemoenzymatic methods. Acknowledgements We thank the Ministerio de Ciencia e Innovación of Spain (CTQ2008-01565/BQU) and the Junta de Andalucía (FQM 345) for financial support. Received: September 21, 2010 [1] a) G. Just, A. Martel, Tetrahedron Lett. 1973, 5, 1517; b) G. Just, K. Grozinger, Tetrahedron Lett. 1974, 4165; c) G. Just, K. 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