OBC, 2014, 12, 4454
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PAPER . 2 0 : 7 1 : 7 0 4 1 0 2 / 9 0 / 4 0 n o Y T I S R E V I N U N A I L E T O T S I R A y b d e d a o l n w o D . 4 1 0 2 l i r p A 9 2 n o d e h s i l b u P
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A stereoselective approach to indolizidine and pyrrolizidine alkaloids: total synthesis of (−)-lentiginosine, (−))-epi epi -lentiginosine -lentiginosine and (−)-dihydroxypyrrolizidine † Shruti Vandana Kauloorkar,a Vishwaj Vishwajeet eet Jha,a Ganesh Jogdandb and Pradeep Kumar*a
Received 28th February 2014, Accepted 29th April 2014
A simple and highly efficient approach to hydroxylated pyrrolizidine and indolizidine is developed from an
DOI: 10.1039/c4ob00461b
steps. Its application to the total synthesis of ( −)-lentiginosine, (−)-epi-1,2-lentiginosine and (−)-dihydroxy-
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pyrrolizidine is also reported.
aldehyde alde hyde as a star starting ting material using organ organocat ocatalyti alytic c and asym asymmetri metric c dihy dihydrox droxylat ylation ion rea reaction ctionss as key
Introduction The synthesis of enantiopure therapeutics with a high medicinal value has always been a prime concern among synthetic chemists. Among them, azasugars have gained much attention in recent years as they mimic carbohydrates. Structurally, they are known to contain fused bicyclic systems with nitrogen at the bridge head and variable ring size based on which they may be classified as indolizidines1 and pyrrolizidines.2 These erent patterns of oxygenation; for instance, “izidines” show diff erent the highly oxygenated castanospermine castanospermine 1 1,, its less hydroxylated congener cong enerss such as lent lentigin iginosine osine 2, epi -lentiginosine -lentiginosine 3, and dihydroxypyrrolizidine 4 or the non-oxygenated ring systems such as coniceine 5, pyrrolizidi pyrrolizidine ne 6, etc., etc., are widespread in plants and microorg microorganisms anisms3 (Fig. 1). Lent Le ntig igin inos osin inee wa wass is isol olaate ted d in 19 1990 90 by El Elbe bein in an and d co co-4 workers from the source source Astralagus Astralagus lentiginosus. It is known to exhibit excellent anti-HIV, anti-tumour and immunomodulating activities apart from being a significant inhibitor of amyloglycosidases with IC50 = 5 μg mL−1. The mechanism of action is rela related ted to inhi inhibitio bition n of the bios biosynth ynthesis esis of glyco glycoprot proteins eins which are responsible for recognitio recognition n and adhesion of exogen5 ff ous agents. E ective ective inhibitors are known to mimic the terminal in al uni unitt of oli oligos gosac accha charid rides es com compet petin ing g wit with h the na natur tural al substrate for occupying the enzyme active site.
a
Division of Organic Chemistry, CSIR-NCL (National Chemical Laboratory), Laboratory), Pune 411008, India. E-mail: [email protected]; [email protected]; Tel: +9102025902050 b Central NMR Facility, CSIR-NCL (National Chemical Laboratory), Pune 411008, India † El Elec ectr tron onic ic su supp pple leme ment ntar aryy in info form rmat atio ion n (E (ESI SI)) av avai aila labl ble. e. Se Seee DO DOI: I: 10.1039/c4ob00461b
4454 | Org. Biom Biomol. ol. Chem. Chem., 2014, 12, 4454– 4454–4460
indolizidine and pyrrolizidine pyrrolizidine alkaloids. Fig. 1 Some indolizidine
Owing to its potent biological activity, lentiginosine and its analogues have attracted a great deal of interest among synthetic organic chemists, in spite of the relatively low degree of hydroxylation as evident from the number of literature reports. Lentiginosine was first synthesized in 1993 by Yoda Yoda et al. 6a from a tartaric acid derived imide. Sever Several al syntheses followed thatt empl tha employed oyed a chir chiral al pool appr approac oach h using tartaric tartaric aci acid, d,6 nitrones, 7 carbohydrates 8 or am amin ino o aci cids ds9 as st star artin ting g materia mat erials. ls. Altho Although ugh the majo majority rity of thes thesee liter literatu ature re repo reports rts have used a chiral pool approach, they proved to be useful protocols for only a limited number of molecules and also involve a large number of synthetic steps. Shibasaki and co-workers were the first to report an enantioselect enantioselective ive approac approach h using a 10a Heck cyclization as a key step. Subsequently a number of groups grou ps ha have ve repo reported rted the synt synthesis hesis of lent lentigin iginosine osine and its analogues using an enantioselective approach.10 Therefore, a general enantioselective enantioselective synthetic approach to severa severall azasugars and the gars their ir unn unnat atur ural al an analo alogue guess tha thatt ar aree am amena enable ble to implemen imple mentati tation on of requ requisite isite ster stereoch eochemic emical al var variati iations ons and diff erent erent forms of substitution has become necessary. We have
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recently reported the synthesis of indolizidine and pyrrolizidinee in our pr din preli elimi minar naryy com commu munic nicat ation ion11 emplo employing ying the sequential α-amination 12 an and d Hor Horner ner– Wadswo Wadsworth rth–Emmons (HWE) olefination as the key step. In continuation of our interest in developing new methodologies 13 using proline catalyzed sequential amination/aminoxylation followed by HWE olefination, we report here a general and e fficient strategy for the synthesis the sis of len lentig tigino inosin sine, e, epi -lenti -lentigin ginosi osine ne an and d dih dihydr ydroxy oxy pyrrolizidine.
Scheme 2 Synthesis of indolizidine indolizidine alkaloid coniceine. coniceine.
Table 1 Optimization of Sharpless asymmetric asymmetric dihydroxylation dihydroxylation reaction conditions
Results and discussion Our general synthetic strategy is outlined in Scheme 1. Lentiginosine 2, epi -lentiginosine -lentiginosine 3 and dih dihydr ydroxy oxy pyr pyrro roliz lizidi idine ne 4 could be obtained by cyclization of A A . Compound A Compound A could could be synthesized by Sharpless asymmetric dihydroxylation14 of the α,β-unsaturated ester B ester B for for the introduction of the two hydroxy group gr oupss adj adjac acent ent to the am amine ine fun funct ction ionali ality ty whi which ch in tur turn n could be synthesized from aldehyde C via via a a proline catalyzed α-ami -aminat nation ion rea reaction ction.. Befor Beforee emba embarkin rking g on the syn synthes thesis is of the target mole molecules cules,, we cons consider idered ed expl explorin oring g a model synthesis to test the devised strategy, in particular, the concomitant cleavage of the N–N bond and nucleophilic displacement underr hydr unde hydrogen ogenati ation on cond conditio itions. ns. The synt synthesi hesiss comm commence enced d with the aldehyde aldehyde 7a which, which, on proline-ca proline-catalyzed talyzed sequential α-ami -aminat nation ion follo followed wed by a HWE olefi olefinat nation, ion, furnished furnished the γ-amino-α,β-unsatur -unsaturated ated ester 8a in 68 68% % yi yiel eld d (9 (91% 1% ee ee). ).15 Compound 8a 8a was then subjected to ester reduction, ensuing double dou ble bon bond d re reduc ductio tion n an and d TBS dep depro rotec tectio tion n in one st step ep using LiBH4 in THF to provide the diol 9. Compound 9 on treatm tre atment ent with tolue toluenesu nesulfony lfonyll chlo chloride ride and trie triethyl thylamin aminee resulted in the formation of ditosylate which was subjected to hydrogenation conditions for the cleavage of N–N bonds using RANEY®-Ni to give the free amine which on nucleophilic displaceme pla cement nt of ditos ditosylat ylatee led to the form formati ation on of indol indolizid izidine ine alkaloid ( R R)-coniceine )-coniceine 5 (Scheme 2). The extrapolation of this strategy allowed the successful completion of the synthesis of all the thr three ee ta targe rgett mol molecu ecules les in a ve very ry short and efficient
Yie ielld (%)
Ratio (10 : 11 11))
1 2 3 4 5 6
N igD an) dPHAL (5 mol%) (DoHlQ 2 (DHQ)2PHAL (5 mol%) (DHQD)2PYR (5 mol%) (DHQD)2 AQN (5 mol%) (DHQ)2 AQN (5 mol%)
9 94 5 93 89 96 96
83 2 :: 1 37 99 : 1 2:3 1:3 99.8 : 0.2
Reactions were carried out in the presence of 1 mol% of OsO 4 and 3 equivalents of K2CO3 and K3FeCN6.
8a (Table 1). At this stage we investigated the use of the Sharp8a (Table less asymmetric dihydroxylation reaction used for embedding two hydroxy groups in the substrate containing a pre-existing chiral centre with a bulky substituent at the allylic nitrogen. The use of cinchona alkaloid ligand variants to achieve the two re requi quisit sitee st ster ereoc eocent entre ress pr prov ovide ided d a gen gener eral al sy synth ntheti eticc pathway to the family of hydroxylated azasugars in a highly diastereoselective diastere oselective manner. Dihydrox Dihydroxylation ylation of 8a of 8a under Sharpless conditions in the absence of a chiral ligand interestingly gave “syn syn facial selectivity ” (syn syn--10 10//anti -11 83/17) where both products were easily separable by silica gel column chromatography. This result showed that the bulk of the allylic NCbz substituent had little impact on the stereodiff erentiation erentiation of the two π faces. The probable explanation for this diastereofacial bias could be attributed to the presence of H-bonding between the OsO4 and NCbz-NHCbz group that facilita facilitates tes the formatio formation n 16 of syn-diastereomer syn -diastereomer 10 as a major product (Fig. 2). We then examined the efficacy of various cinchona alkaloid containing ligands and the results are summarized in Table 1. To achieve the “anti facial facial selectivity ” (based on the Sharpless mnemonic device)) we use device used d (DH (DHQD QD))2PHAL PHAL,, surpr surprisin isingly gly the dias diaster tereoeomeric outcome (anti (anti -11 11//syn syn--10 10)) was found to be 3/2. Switching the ligand to (DHQD)2PYR gave a similar result (anti (anti -11 11//syn syn--10 10 3/2). 3/2).
route ro ute to ind indoli olizid zidine ine and pyr pyrrol rolizi izidin dine e
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Ligandsa
a
manner. The synthesis of the target molecules (− (−)-lentiginosine and its 1,2-epimer commenced with γ-amino-α,β-unsatur -unsaturated ated ester
Scheme 1 Retro Retrosy synth ntheti etic c alkaloids (2 (2–4).
Entry
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Fig. 2 Proposed transition state for syn selectivity.
Finally, (DHQD)2 AQN was found to be a better ligand as the dr for the anti anti compound compound 11 11 increased increased to 3/1. To favour the “syn antipode” both (DHQ)2PHAL and (DHQ (DHQ))2 AQN were found to be useful ligands. In these cases, the reaction progressed with high diastereoselectivity and we obtained syn syn--10 essentially as a single diastereomer (Table 1, entries 3 and 6). In all the cases, however, the yield remained almost the same. The relative stereochemistry of the three stereocenters generated were unambiguously determined using 2D NMR spectroscopy. For this purpose, diols 10 10 and and 11 11 were subjected to hydrogenation conditions using RANEY®-Ni to cleave the N –N bond bon d to obt obtai ain n fr free ee am amine ine whi which ch sub subseq sequen uently tly und underg ergoes oes cycliza cycl ization tion to giv givee cycl cyclic ic deri derivat vative ivess 12 and 13 13,, respectiv respectively ely (Scheme 3). Extensive NMR studies were carried out on com-
Fig. 3 NOESY spectrum spectrum of compound compound 12 12..
β- and γ -position. The NOESY spectra of compound 12 show a cross peak between the β and γ protons which confirmed their syn relationship relationship between the β and γ methine methine prot protons, ons, the α and β protons did not show NOESY correlation which indi-
pounds 12 and pounds 12 and 13 13 to to determine the relativ relativee stereoc stereochemistry hemistry.. cated their trans their trans relationship relationship as shown in Fig. 3. For compound compound 13 13,, the α, β, γ protons resonated at δ 4.06, The two cycl cyclic ic isom isomers ers 12 and 13 were were sub subjec jected ted to 2D 3.77 and 3.28 respectively. The α proton showed as a distinct NMR spectroscopy after carefully studying their peak patterns double dou blett at 4.0 4.06 6 ppm having having a cou coupli pling ng con const stan antt of 7.3 Hz in 1D NMR. 1H, 13C and DEPT NMR spectra of the cyclized which indicate indicated d the trans stereochemistry stereochemistry between α and compounds were determined in CDCl3. Initially, it was found β methine protons. The β and γ protons showed multiplet like that compound 13 showed showed resolved resolved peaks for the methine patterns patt erns whic which h proh prohibite ibited d extr extract action ion of their coupling conprotons α , β and γ whereas this was not the case for compound stants. Therefore the 2D NOESY spectrum was used to find out 12.. Acetone-d6 proved to be a more suitable solvent for better 12 the rela relative tive ster stereoch eochemis emistry try at the β and γ positions. positions. The quality NMR spectra. Compounds 12 Compounds 12 and and 13 13 were were then characNOESY NOES Y spec spectra tra of comp compound ound 13 did not show a corr correla elation tion terized using the 1D NMR experiments ( 1H, 13C DEPT) as well between the β and γ protons which confirmed their anti their anti stereo stereoas 2D homo homonucl nuclear ear (CO (COSY SY,, and NOE NOESY) SY) and hete heteron ronucle uclear ar chemistry. The α and β protons did not show NOESY corre(HSQC and HMBC) NMR spectroscopy. lation which indicated the trans the trans relationship relationship between them as For compound compound 12 12,, the α, β, γ protons resonated at δ 4.04, shown in Fig. 4. 4.22 and 3.55 ppm respectively. The α proton shows the dis After determinin determining g the relativ relativee stereoc stereochemistry hemistry of comtinct doublet at 4.04 ppm having a coupling constant of 6.63 pounds 12 and 13 13,, we pr proce oceede eded d to the synthes synthesis is of tar target get Hz whi which ch in indic dicat ated ed the trans stereochem stereochemist istry ry betw between een the molecules. For the synthesis of (− ( −)-1,2)-1,2-epi epi -lentiginosine 3 -lentiginosine 3,, diol α and β-methine protons. The β and γ-protons showed multi10 was subjected to LiBH4 reduction to give tetrol 14 14.. Complet like pattern which prohibited extraction of the coupling pound 14 pound 14 was subjected to selective primary tosylation using constan cons tants ts fro from m the 1D spect spectrum. rum. Therefor Thereforee the 2D NOE NOESY SY TsCll an TsC and d Et 3N to giv givee the ditosyl, ditosyl, whi which ch wa wass sub subjec jected ted to spectrum was used to determine the relative stereochemistry at the hydrogenation conditions using freshly prepared RANEY®-Ni to deliver the free amine which on nucleophilic displacement of ditosylate led to the formation of the desired (− ( −)-1,2)-1,2-epi epi lentiginosine 3 lentiginosine 3 (Scheme (Scheme 4). In a similar way, as illustrated in Scheme 5, (− ( −)-lentiginosine 2 sine 2 was synthesized from diol 11 diol 11 by an analogous series of reactions to those shown in Scheme 4. The strategy can also be extended to the synthesis of the natural enantiomer and other stereoisomers by simply using the other enantiomer of proline
Scheme 3 Prepar Preparation ation of cyclic derivatives. derivatives.
4456 | Org. Biomol. Chem., 2014, 12, 4454– 4454–4460
for the α -amination and diff erent erent ligands for dihydroxyla dihydroxylation. tion. After the successful completion completion of the synthesis synthesis of lentig lentiginoinosine and its 1,2-epimer we thought to extrapolate our strategy
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Scheme 6 Synthesis of dihydroxy dihydroxy pyrrolizidine. pyrrolizidine.
compound 2 with with an overall overall yield of 23% and tar target get compound 4 pound 4 with with an overall yield of 23%. This strategy is the shortest syn synthesi thesiss repo reported rted so far from easily available available sta startin rting g materials with high yields.
Fig. 4 NOESY spectrum spectrum of compound compound 13 13..
Conclusions In conclusion, we have developed a new, highly efficient and concise protocol to synthesise dihydroxylated indolizidine and pyrrolizidine alkaloids using a proline catalyzed α-amination followed by Sharpless asymmetric dihydroxylation reaction as the key steps. Its utility was illustrated by the total synthesis of (−)-lentiginosine, (− (−))-epi epi -lentiginosine -lentiginosine and (− (−)-dihydroxypyrrolizidine. The synthetic strategy allows implementation of the desi de sira rabl blee st ster ereo eoce cent nter erss at CC-1, 1, CC-2 2 an and d CC-8a 8a an and d ca can n be exten ex tended ded to the sy synth nthesi esiss of oth other er ste stere reois oisome omers rs an and d an anaalogu lo gues es wi with th va vari riab able le ri ring ng si size zess an and d diff erent erent deg degre rees es of hydroxylation.
Scheme 4 Synthesis of 1,2-epi -lentiginosine. -lentiginosine.
Experimental section Dibenzyl ( R, E )-1-(8-(( )-1-(8-((tert -butyldimethylsilyl)oxy)-1-ethoxy-1-butyldimethylsilyl)oxy)-1-ethoxy-1oxooct-2-en-4-yl)hydrazine-1,2-dicarbox oxooct-2-en-4-yl)hydrazin e-1,2-dicarboxylate ylate (8a) (For a procedure to prepare 8a prepare 8a,, see ref. 11.) [α ]25 (c 1.0, D : +2.67 (c CHCl3) HPLC: Kromasil 5-Amycoat (250 × 4.6 mm) (2-propanol–pe petr trol oleu eum m et ethe herr = 10 : 90 90,, fl flow ow rate rate 0. 0.5 5 mL mi min n−1, λ = 230 nm) nm).. Re Reten tentio tion n tim timee (mi (min): n): 13. 13.30 30 (ma (major jor)) an and d 16. 16.23 23 (minor). The racemic standard was prepared in the same way using DL DL -proline as a catalyst. ee 91%.
Scheme 5 Synthesis of (−)-lentiginosine.
to other analogues. Thus, by simply altering the chain length, the syn synthe thesis sis of dih dihydr ydroxy oxy pyr pyrro roliz lizidi idine ne 4 was ach achiev ieved. ed. As illustra illustrated ted in Scheme 6, the synthesis started with the aldehyde 7b aldehyde 7b,, which on sequential α -amination followed by HWE olefination furnished the γ-amino-α,β-unsaturated ester ester 8b 8b in 68% yield and 94% enan enantiose tioselect lectivity ivity..15 The olefinic compound 8b pound 8b was subjected to Sharpless asymmetric dihydroxylation using (DHQD)2 AQN as the ligand to give the diol diol 16 16.. Diol 16 was was conv converted erted to give the targ target et comp compound ound 4 using the
( R, E )-Dibenzyl )-Dibenzyl 1-(7-((tert -butyldimethylsilyl)oxy)-1-ethoxy-1-butyldimethylsilyl)oxy)-1-ethoxy-1oxohept-2-en-4-yl)hydrazine-1,2-dicarbox oxohept-2-en-4-yl)hydrazi ne-1,2-dicarboxylate ylate (8b) (For a procedure to prepare prepare 8b 8b see see ref. 11.) [α ]25 (c 1.0, D : +4.73 (c CHCl3) HPLC: Kromasil 5-Amycoat (250 × 4.6 mm) (2-propanol–pet ether ether = 10 : 90, flow flow rate rate 0.5 mL min−1, λ = 254 nm).
same set of reactions as described in Schemes 3 and 4. Our synthetic approach aff orded orded the target compound 3 compound 3 in a linear sequence of 4 steps with an overall yield of 31%, target
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Retention time (min): 13.46 (major) and 18.07 (minor). The race ra cemi micc st stan anda dard rd wa wass pr prep epar ared ed in th thee sa same me wa wayy us usin ing g 11 DL-proline as a catalyst, ee 94%.
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Dibenzyl ( R)-1-(1,8-dihydr )-1-(1,8-dihydroxyoctan-4 oxyoctan-4-yl)hydrazine-1,2-yl)hydrazine-1,2dicarboxylate dicarboxyla te (9)
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(200 MHz, CDCl3): δ 0.00 (m, 6H), 0.82–0.91 (m, 9H), 1.22–1.54 (m,, 8H (m 8H), ), 1. 1.78 78–1. 1.98 98 (m (m,, 1H 1H), ), 3. 3.55 55–3. 3.64 64 (m (m,, 2H 2H), ), 3. 3.90 90–4.09 (m, 1H), 4.14–4.38 (m, 3H), 4.90–5.34 (m, 4H), 6.68–6.84 (m, 1H), 7.26–7. 7.45 45 (m (m,, 10 10H) H).. 13C NMR (50 MHz, CDCl3): −5.3, 14.1 14 .1,, 18 18.3 .3,, 25 25.9 .9,, 25 25.8 .8,, 31 31.4 .4,, 32 32.3 .3,, 61 61.8 .8,, 62 62.4 .4,, 67 67.8 .8,, 68 68.5 .5,, 70.3, 70.4, 72.9, 127.8, 128.0, 128.2, 128.3, 128.5, 135.5, 156.6, 156.9, 172.8. MS (ESI): m (ESI): m// z 655.29 655.29 (M + Na)+ HRMS (ESI) m (ESI) m// z : + [M + Na] Ca Calc lcd d fo forr C32H48O9N2SiN SiNa a 655 655.3 .3021 021;; Fo Found und 655.3018. HPLC: Kromasil RP-18 (150 × 4.6 mm) (methanol–H2O =
To a sol soluti ution on of eth ethyl yl es ester ter 8a (0.5 (0.5 g, 0. 0.80 80 mmol) mmol) in THF (7 mL) was added LiBH4 (0.035 g, 1.6 mmol) at 0 °C. The reaction mixture was stirred at rt for 2 h. It was then quenched with ice-cold aq. HCl (1 N) and extra extracted cted with ethyl acetate (3 × 5 mL). The combined organic layers were washed with brine, dried drie d ov over er anh anhyd. yd. Na2SO4 and conc concentr entrate ated d unde underr red reduced uced pressure to give the crude product. Silica gel column chromatogr at ograph aphyy of the cru crude de pr produ oduct ct usi using ng eth ethyl yl ac aceta etate te as the 85 : 15 15,, flow flow ra rate te 1 mL min min−1, λ = 254 nm). Retention time eluent gave 9 gave 9 as a waxy solid (0.312 g, yield 84%). [ α ]25 D : +0.32 (c 1.0, CHCl3), IR (CHCl3, cm−1): νmax 3289, 2292, 1709, 1662, (min): 7.33 and 8.23. 1218. 1H NMR (200 MHz, CDCl 3): δ 1.26–1.60 (m, 10H), 1.96 (brs, (br s, 2H) 2H),, 3.4 3.47 7–3.6 3.67 7 (m, 4H), 4.0 4.02 2–4.2 4.29 9 (m, 1H), 4.9 4.96 6–5.26 Dibenzyl 1-((2S ,3 ,3 R,4 R)-7-((tert -butyldimethylsilyl)oxy)-1-ethoxy-butyldimethylsilyl)oxy)-1-ethoxy 13 (m, 4H), 7.04 (brs, 1H), 7.31–7.35 (m, 10H). C NMR (100 MHz, 2,3-dihydroxy-1-oxoheptan-4-yl)hydrazine-1,2-dicarboxylate (16) CDCl3): as a rotameric mixture δ 22.1, 25.5, 28.7, 29.3, 29.7, g, 95%, dr 3 : 1); [α ]25 (c 1.0, CHCl3) D : +10.96 (c 31.9, 32.6, 61.8, 62.2, 62.3, 62.8, 67.7, 67.8, 67.9, 68.3, 127.6, Waxy solid (0.378 max −1 3456, 2956, 2857, 1731, 1416. 1H NMR 128.0, 128. 0, 128. 128.2, 2, 128. 128.3, 3, 128. 128.4, 4, 128. 128.5, 5, 135. 135.5, 5, 135. 135.8, 8, 136. 136.0, 0, 156. 156.4, 4, IR (CHCl3, cm ): ν 156.8, 156.9, 157.3. MS (ESI): m (ESI): m// z z 467.15 467.15 (M + Na)+ HRMS (ESI) (200 MHz, CDCl3): δ −0.02 (m, 6H), 0.80 (m, 9H), 1.17–1.31 m/ z z : [M + H]+ Calcd for C24H33O6N2 445.2333; Found 445.2328. (m, 3H), 1.38–1.68 (m, 3H), 1.87–2.03 (m, 1H), 3.28–3.68 (m, 3H), 3.85–3. 3.99 99 (m (m,, 1H 1H), ), 4. 4.16 16–4. 4.30 30 (m (m,, 3H 3H), ), 4. 4.86 86–5. 5.27 27 (m (m,, 4H 4H), ), Dibenzyl 1-((2 R,3S ,4 ,4 R)-8-((tert -butyldimethylsilyl)oxy)-1-ethoxy-butyldimethylsilyl)oxy)-1-ethoxy- 7.26 (m, 10H), 7.48–7.70 (m, 1H). 13C NMR (50 MHz, CDCl3): 2,3-dihydroxy-1-oxooctan-4-yl)hydra 2,3-dihydr oxy-1-oxooctan-4-yl)hydrazine-1,2-dica zine-1,2-dicarboxylate rboxylate (10) δ − −5.6, 5.6, 13.9, 18.2, 25.8, 28.7, 60.2, 61.6, 62.2, 68.0, 68.3, 70.9, 71.8, 71.8 , 126. 126.8, 8, 127. 127.5, 5, 127. 127.7, 7, 128. 128.0, 0, 128. 128.3, 3, 128. 128.4, 4, 135. 135.0, 0, 135. 135.7, 7, General procedure for Sharpless asymmetric dihydroxylation: +
To a mixt xtur uree of K3Fe(CN)6 (0.8 (0.825 25 g, 2. 2.50 50 mm mmol), ol), K2CO3 (0.345 g, 2.50 mmol), and (DHQ)2 AQN (6.5 mg, 1 mol%) in t -BuOH -BuOH–H2O (1 : 1, 10 mL) at 0 °C was added added osmium osmium tetroxide tetroxide (0.32 mL, 0.1 M solution in toluene, 0.4 mol%), followed by methane sulfonamide (0.079 g, 0.83 mmol). After stirring for 5 min at 0 °C, the olefin 8a 8a (0.500 (0.500 g, 0.83 mmol) was added in one portion. The reaction mixture was stirred at 0 °C for 24 h and then quenched with solid sodium sulfite (0.5 g). Stirring was continued for an additional 15 min and then the solution was extra extracted cted with EtOAc (3 × 20 mL). The combined extra extracts cts were washed with brine, dried over Na2SO4 and concentrated. Silica Sili ca gel colum column n chr chroma omatogr tography aphy puri purifica fication tion ( Rf = 0.4 0.40, 0, EtOAc–petr petroleum oleum ether, ether, 3 : 7) of the crude product product gave gave 10 10 as as a 25 white waxy solid (0.507 g, 96%). [α ]D : +0.22 (c (c 1.0, CHCl3), IR max −1 (CHCl3, cm ): ν 3474, 3250, 3036, 2925, 2855, 1718, 1682, 1462. 1H NMR (200 MHz, CDCl3): δ −0.01 (m, 6H), 0.85 (m, 9H), 1.21–1.3 1.32 2 (m, 6H), 1.3 1.39 9–1.53 (m, 3H), 3–3.2 3.29 9 (m, 1H), 3.45–3.82 (m, 3H), 4.02–4.17 (m, 1H), 4.27 (q, (q, J J = 7 Hz, 2H), 5.04–5.3 5.34 4 (m, 4H), 6.6 6.68 8–7.0 7.02 2 (m, 1H), 7.1 7.14 4–7.3 7.37 7 (m, 10H 10H). ). 13 δ C NMR (50 MHz, CDCl3): − −5.3, 5.3, − −5.4, 5.4, 14.1, 18.3, 21.7, 25.9, 31.8, 61.8, 62.2, 68.5, 71.1, 71.3, 71.9, 72.1, 127.7, 127.9, 128.1, 128.2, 128.3, 128.5, 128.6, 134.9, 135.7, 156.0, 157.1, 172.7. MS (ESI): m/ z 655.29 (ESI): 655.29 (M + Na)+ HRMS (ESI) (ESI) m/ z z : [M + Na]+ Calcd for C32H48O9N2SiNa 655.3021; Found 655.3018. HPLC: Kromasil RP-18 (150 × 4.6 mm) (methanol–H2O = 85 : 15 15,, flow rate rate 1 mL min min−1, λ = 254 nm). Retention time (min): 6.42 and 7.43.
156.1, 156.9, 172.7. MS (ESI): m (ESI): m// z z 641.31 641.31 (M + Na) HRMS (ESI) m/ z z : [M + Na]+ Ca Calcd lcd for C31H46O9N2SiNa 641. 641.2868 2868;; Fou Found nd 641.2869. HPLC: Kromasil RP-18 (150 × 4.6 mm) (methanol–H2O = 85 : 15 15,, flow flow ra rate te 1 mL min min−1, λ = 254 nm). Retention time (min): 6.18 and 7.28.
2,3-dihydroxy-1-oxooctan-4-yl)hydrazine-1,2-dica 2,3-dihydroxy-1-oxooctan-4-yl)hydra zine-1,2-dicarboxylate rboxylate (11) Waxyy solid (0.380 g, 96%, dr 3 : 1); [α ]25 Wax (c 1.0, CHCl3), D : +8.04 (c −1 max IR (CHCl3, cm ): ν 3748, 3421, 3019, 1734, 1541. 1H NMR
55.1, 62.9, 74.1, 74.9, 175.4. MS (ESI): m/ z z 326.18 (M + Na) HRMS (ESI) m (ESI) m// z : [M + H]+ Calcd for C14H29O4NSiNa 326.1758; Found 326.1764.
(3 R,4S ,5 ,5 R)-5-(4-((tert -Butyldimethylsilyl)oxy)butyl)-Butyldimethylsilyl)oxy)butyl)3,4-dihydroxypyrrolidin-2 3,4-dihydrox ypyrrolidin-2-one -one (12)
General procedure for cyclization: Determination of relative configuration: a solution of compound 10 compound 10 in MeOH (10 mL) and acetic acid (5 drops) was treated with RANEY® nickel (1 g, excess) under a H2 (60 psi) atmosphere for 24 h. The reaction mixture was then filtered over celite and concentrated to the give the crude free amine which was further subjected to cyclisation by stirring in EtOH at 55 °C for 5 h. The reaction mixture was concentrated in vacuo to give the crude cru de pr produ oduct. ct. Sil Silica ica gel col column umn chr chroma omatog togra raphy phy (et (ethyl hyl acetate–pet petro roleu leum m eth ether/ er/6 6 : 4) of the cr crude ude pr produc oductt ga gave ve 25 12 as 12 as a syrupy liquid (0.359 g, 75%). [α ]D : +31.25 (c (c 0.5, CHCl3) IR (C (CHC HCll3, cm−1): νmax 32 3285 85,, 29 2930 30,, 28 2858 58,, 17 1712 12,, 12 1255 55.. 1 H NM NMR R (2 (200 00 MH MHz, z, CD CDCl Cl3): δ 0.05 0.05 (s (s,, 6H 6H), ), 0. 0.89 89 (s (s,, 9H 9H), ), 1.29–1. 1.56 56 (m (m,, 5H 5H), ), 1. 1.71 71–1. 1.89 89 (m (m,, 1H 1H), ), 3. 3.60 60–3. 3.66 66 (m (m,, 3H 3H), ), 1 4.24–4. 4.45 45 (m (m,, 2H 2H), ), 6. 6.29 29 (b (brs rs,, 1H 1H). ). H NMR (5 (500 00 MHz, acetone-d6): δ 0.07 (s, 6H), 0.91 (s, 9H), 1.40 (m, 2H), 1.56 (m, 3H), 1.81 (m, 1H), 2.92 (brs, 2H), 3.58 (m, 1H), 3.67 (t, J = 5. J 5.72 72 Hz Hz,, 2H 2H), ), 4. 4.06 06 (d (d,, J J = 5. 5.35 35 Hz Hz,, 1H 1H), ), 4. 4.25 25 (m (m,, 1H 1H). ). Dibenzyl 1-((2S ,3 ,3 R,4 R)-8-((tert --butyldimethylsilyl)oxy)-1-ethoxybutyldimethylsilyl)oxy)-1-ethoxy- 13C NMR (50 MHz, CDCl ): δ − −5.3, 5.3, 18.4, 22.5, 25.9, 29.7, 32.5, 3 +
4458 | Org. Biom Biomol. ol. Chem. Chem., 2014, 12, 4454– 4454–4460
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Organic & Biomolecular Chemistry
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,4 R,5 R)-5-(4-((tert -Butyldimethylsilyl)oxy)butyl)-3,4-Butyldimethylsilyl)oxy)butyl)-3,4(3S ,4 dihydroxypyrrolidin-2-one dihydroxypy rrolidin-2-one (13)
. 2 0 : 7 1 : 7 0 4 1 0 2 / 9 0 / 4 0 n o Y T I S R E V I N U N A I L E T O T S I R A y b d e d a o l n w o D . 4 1 0 2 l i r p A 9 2 n o d e h s i l b u P
(m, 2H (m, 2H), ), 1. 1.70 70–1. 1.90 90 (m (m,, 2H 2H), ), 3. 3.54 54–3. 3.66 66 (m (m,, 5H 5H), ), 3. 3.83 83–4.05 (m,, 1H (m 1H), ), 4. 4.15 15–4. 4.40 40 (m (m,, 1H 1H), ), 5. 5.05 05–5. 5.15 15 (m (m,, 4H 4H), ), 7. 7.10 10–7.36 13 (m, 10H). C NMR (125 MHz, CDCl3): as a rotameric mixture δ 23.3, 33.5, 34.1, 63, 64.6, 68.5, 69.3, 72.7, 75.6, 77.5, 80.2, 128.0, 128. 0, 128. 128.7, 7, 129. 129.1, 1, 129. 129.2, 2, 129. 129.4, 4, 129. 129.5, 5, 129. 129.6, 6, 129. 129.7, 7, 137. 137.5, 5, 137.7, 137. 7, 143. 143.5, 5, 157. 157.7, 7, 158. 158.8. 8. MS (ESI): (ESI): m/ z z 485. 485.22 22 (M + Na Na))+ HRMS (ESI) m (ESI) m// z z : [M + Na]+ Calcd for C23H30O8N2Na 485.1894; Found 485.1891.
Syrupy liq Syrupy liquid uid (0. (0.180 180 g, 75% 75%); ); [α ]25 (c 0.5, CHCl3) IR D : +3.77 (c max −1 (CHCl3, cm ): ν 3354,, 2922 3354 2922,, 1711 1711,, 1463 1463,, 1377 1377.. 1H NMR (200 (20 0 MH MHz, z, CD CDCl Cl3): δ 0.05 0.05 (s (s,, 6H 6H), ), 0. 0.89 89 (s (s,, 9H 9H), ), 1. 1.50 50–1.53 (m, 4H), 1.7 1.73 3–2.1 2.12 2 (m, 2H), 3.3 3.31 1–3.4 3.42 2 (m, 1H), 3.63 (t, J J = 5.9 Hz, 2H), 3.87–3.94 (m, 1H), 4.29–4.32 (m, 1H), 6.67 (brs, 1H) 1 H NMR (500 MHz, acetone-d6): δ 0.07 (s, 6H), 0.91 (s, 9H), 1.51–1. 1.58 58 (m (m,, 5H 5H), ), 1. 1.75 75 (m (m,, 1H 1H), ), 2. 2.94 94 (b (brs rs,, 2H 2H), ), 3. 3.26 26–3.30 (m, 1H), 3.67 (t, (t, J J = = 6.10 Hz, 2H), 3.77 (m, 1H), 4.06 (d, J J = 13 7.3 Hz, 1H). C NMR (125 MHz, CDCl3): δ −5.3, 18.3, 22.1, 25.9, 25. 9, 32. 32.5, 5, 33. 33.3, 3, 56. 56.8, 8, 62. 62.9, 9, 76. 76.3, 3, 79. 79.8, 8, 175 175.3. .3. MS (ES (ESI): I): m/ z z + + 326. 32 6.15 15 (M + Na Na)) HRM HRMS S (ES (ESI) I) m/ z z : [ M + N a ] Cal Calcd cd for C14H29O4NSiNa 326.1758; Found 326.1764.
(1S ,2 ,2S ,8a ,8a R)-Octahydr )-Octahydroindolizine-1, oindolizine-1,2-diol 2-diol (3)
General procedure for cyclization: To an ice-cold stirred solution of of 14 (0.25 (0.25 g, 0.5 mm mmol) ol) an and d tri trieth ethyla ylami mine ne (0. (0.22 22 mL mL,, 1.5 mmol) in anhydrous CH2Cl2 (6 mL) was added toluenesulfonyl chloride (0.20 g, 1.0 mmol) over 15 min. The resulting mixture mixt ure was allo allowed wed to war warm m up to roo room m tempe tempera ratur turee and Dibenzyl 1-((2S ,3 ,3S ,4 ,4 R)-1,2,3,8-tetrahydroxyoctan-4-yl) stirred for 48 h. After diluting with 6 mL CH 2Cl2, the solution hydrazine-1,2-dicarbox hydrazi ne-1,2-dicarboxylate ylate (14) was washed with water (3 × 15 mL), brine, dried over anhyd. General procedure for LiBH4 reduction: To a solution of ethyl Na2SO4 and concentrated to give the crude ditosylated product ester 10 10 (0.5 (0.5 g, 0.79 mmol) in THF (7 mL) was added LiBH 4 which was subjected to the next step without further (0.05 g, 0.24 mmol) at 0 °C. The reaction mixture was stirred at purification. A solution of crude tosylat tosylated ed compound in MeOH (10 mL) rt for 2 h. It wa wass th then en quenc quenche hed d wi with th aq. HC HCll (1 N) an and d extracted with ethyl acetate (3 × 5 mL). The combined organic and acetic acid (5 drops) was treated with RANEY® nickel (1 g, layers were washed with brine, dried over anhyd. Na 2SO4 and excess) under a H2 (60 psi) atmosphere for 24 h. The reaction conc co ncen entr tra ate ted d un unde derr re redu duce ced d pr pres essu sure re to gi give ve th thee crud crudee mixture was then filtered over celite and concentrated to give product. produ ct. Sil Silica ica gel col column umn chr chroma omatog togra raphy phy (me (metha thanol nol– CH2Cl2: 1 : 20) of the crude crude pr produ oduct ct gave gave 14 as a white solid (0.3 (0 .32 2 g, yi yiel eld d 85 85%) %).. mp mp:: 12 123 3–12 125 5 °C °C;; [α ]25 +0.1 .13 3 (c 0.3, D : +0 max −1 CH3OH), IR (CHCl3, cm ): ν 3384, 3282, 3019, 2926, 1749, 1 1720,, 1646 1720 1646,, 1215 1215.. H NM NMR R (2 (200 00 MH MHz, z, CD CDCl Cl3): δ 1.32–1.58 (m, 6H), 3.45–3.68 (m, 6H), 4.5–4.59 (m, 1H), 5.02–5.24 (m, 4H), 7.24–7.44 (m, 10H). 13C NMR (50 MHz, CDCl3): as a rotameric mixture 23.4, 30.5, 30.8, 33.1, 33.3, 62.8, 65.0, 69.1, 69.2, 69.4, 71.7, 71.8, 72.2, 72.5, 128.7, 129.1, 129.3, 129.4, 129.7, 137.4, 137.7, 137. 7, 158. 158.6, 6, 158. 158.7, 7, 158. 158.9. 9. MS (ESI (ESI): ): m/ z z 499.17 (M + Na)+ + HRMS (ESI) m (ESI) m// z : [M + Na] Calcd for C24H32O8N2Na 499.2051; Found 499.2047.
crude free amine which was further subjected to cyclization by stirring in EtOH at 55 °C for 20 h. The reaction mixture was concentrated in concentrated in vacuo to vacuo to give the crude product. Silica gel (neutralized) column chromatography (methanol–CH2Cl2: 1 : 15) of of the crude product gave 3 gave 3 as a white solid (0.046 g, 56%). mp: 6e 134–136 °C [lit.: 137–138]; [α ]25 (c 1, CH3OH). [lit.:6e D : −6.48 (c 25 1 [α ]D : −5.3 (c 0.3, 0.3, CH3OH)]; H NMR (200 MHz, D2O): δ 1.34–1. 1.55 55 (m (m,, 3H 3H), ), 1. 1.67 67–1. 1.88 88 (m (m,, 3H 3H), ), 2. 2.16 16–2. 2.34 34 (m, 2H 2H), ), 2.42–2.49 (m, 1H), 3.15 (d, J (d, J = = 11.2 Hz, 1H), 3.52 (dd, J (dd, J = = 7 Hz, 11.2 11 .2 Hz Hz,, 1H 1H), ), 3. 3.98 98 (d (d,, J J = 4. 4.1 1 Hz Hz,, 1H 1H), ), 4. 4.08 08–4. 4.15 15 (m (m,, 1H 1H). ). 13 C NMR (50 MHz, D2O): 25.0, 25.9, 26.0, 55.1, 62.1, 69.6, 77.9, 80.6. (1H and 13C NMR data were in good agreement with those reported in lit.6e). MS (ESI): (ESI): m/ z 158.11 z 158.11 (M + H)+ HRMS (ESI) m/ z z : [M + H]+ Calcd for C8H16O2N 158.1176; Found 158.1175.
Dibenzyl 1-((2 R,3 R,4 R)-1,2,3,8-tetrahydroxyoctan-4-yl) hydrazine-1,2-dicarbox hydrazi ne-1,2-dicarboxylate ylate (15)
(1 R,2 R,8a R)-Octahydr )-Octahydroindolizine-1,2 oindolizine-1,2-diol -diol (2) White solid (0.32 g, yield 85%); mp: 116–118 °C; [α ]25 D : +0.34 5a 1 max − White solid (0.047 g, 57%). mp: 106 106–107]; –108 °C [lit.: (c 0.85, 0.85, CH3OH OH), ), IR (CH (CHCl Cl3, cm ): ν 3384,, 3282 3384 3282,, 3019 3019,, 25 5a 23 1 −2.92 2.92 (c (c 0.5, CH3OH), [lit.: [α ]D −1.6 (c (c 0.24, CH3OH), 2926, 1749, 1720, 1646, 1215, 760. H NMR (200 MHz, CDCl3): [α ]D : − 7c 1 (c 1.0, 1.0, CH3OH)]. H NMR (200 MHz, D2O): δ 1.36–1.4 1.41 1 (m, 1H), 1.4 1.49 9–1.6 1.66 6 (m, 5H), 3.4 3.48 8–3.6 3.69 9 (m, 6H), lit. [α ]D −3.05 (c 1.34 4 (m, 2H), 1.4 1.47 7–1.5 1.53 3 (m, 1H), 1.6 1.68 8–1.7 1.70 0 (m, 1H), 4.16–4.3 4.36 6 (m, 1H), 5.0 5.02 2–5.2 5.24 4 (m, 4H), 7.2 7.29 9–7.4 7.47 7 (m, 10H 10H). ). δ 1.28–1.3 13 1.82 – 1.86 (m, 1H), 1.94 – 1.98 (m, 1H), 2.13 – 2.27 (m, 2H), 2.81 C NMR (100 MHz, CDCl3): as a rotameric mixture δ 27.1, (dd, J J = = 7.59, 11.3 Hz, 1H), 2.94 (d, J (d, J = = 11.3 Hz, 1H), 3.06 (d, J (d, J = = 30.5, 31.1, 33.8, 33.9, 63.0, 63.2, 63.3, 68.7, 69.4, 69.7, 71.8, (dd, (dd, J = = 3.4, 9.1 Hz, 1H) 4.10 –4.13 (m, 1H). 72.2, 72.4, 128.9, 129.3, 129.4, 129.5, 129.6, 129.7, 129.9, 137.9, 11.7 Hz, 1H), 3.70 (dd, J 13 + C NMR (50 MHz, D2O): 25.5, 26.4, 29.9, 55.4, 62.7, 71.4, 78.1, 138.0, 138. 0, 158. 158.5, 5, 158. 158.9, 9, 159. 159.1. 1. MS (ESI (ESI): ): m/ z z 499.22 (M + Na) 1 13 + HRMS (ESI) m (ESI) m// z : [M + Na] Calcd for C24H32O8N2Na 499.2051; 85.1. ( H and C NMR data were in good agreement with those reported in lit.10 g ). MS (ESI): (ESI): m/ z z 158.11 158.11 (M + H)+ HRMS (ESI) Found 499.2047. m/ z z : [M + H]+ Calcd for C8H16O2N 158.1176; Found 158.1174. Dibenzyl 1-((2 R,3 R,4 R)-1,2,3,7-tetrahydroxyheptan-4-yl) hydrazine-1,2-dicarbox hydrazi ne-1,2-dicarboxylate ylate (17) (1 R,2 R,7a R)-Hexahydro-1 H -pyrrolizine-1,2-diol -pyrrolizine-1,2-diol (4) 25
8
White solid (0.32 g, yield 85%); mp: 125–127 °C; [α ]D : −0.19 max −1 (c 0.55, CH3OH). IR (CHCl3, cm ): ν 3376, 3280, 3022, 2929, 1716,, 1638 1716 1638,, 1190 1190.. 1H NM NMR R (2 (200 00 MH MHz, z, CD CDCl Cl3): δ 1.27–1.44
This journal is © The Royal Society Society of Chemistry 2014
Colorless solid (0.047 g, 56%). mp:8 f 138 –24 140 °C [lit.: f 141–143]; 25 [α ]D : −6.67 (c (c 1.3, CH3OH), [lit. [lit.:: [α ]D −6.4 (c (c 1, CH3OH), lit.10e [α ]D +7.6 (c 1.3, CH3OH)]. 1H NMR (200 MHz, CD3OD):
Org. Biomol. Chem., 2014, 12, 4454– 4454–446 4460 0 | 4459
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Paper δ 1.63 1.63–1.80
. 2 0 : 7 1 : 7 0 4 1 0 2 / 9 0 / 4 0 n o Y T I S R E V I N U N A I L E T O T S I R A y b d e d a o l n w o D . 4 1 0 2 l i r p A 9 2 n o d e h s i l b u P
(m, 2H), 1.84–1.99 (m, 2H), 2.50 (dd, J (dd, J = = 7 Hz, 10.7 Hz,, 1H Hz 1H), ), 2. 2.63 63–2. 2.74 74 (m (m,, 1H 1H), ), 2. 2.84 84–2. 2.92 92 (m (m,, 1H 1H), ), 3. 3.14 14–3.19 (m, 1H), 3.23–3.26 (m, 1H), 3.60 (t, J (t, J = = 5.6 Hz, 1H), 3.94 –4.05 (m, 1H). 13 C NMR (50 MHz, CD3OD): 26.4, 31.5, 56.8, 59.7, 71.0, 78.8, 82.9 (1H and 13C NMR data were in good agreement with those reported in lit.8 f ). MS (ESI): (ESI): m/ z z 144.12 144.12 (M + H)+ HRMS (ESI) m/ z : [ M + H ]+ Ca Calc lcd d fo forr C7H14O2N 144 144.10 .1019; 19; Fou Found nd 144.1020.
Organic & Biomolecular Chemistry
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Acknowledgements SVK and VJ thank UGC, New Delhi for research fellowships. We thank Ms S. Kunte for HPLC analysi analysis. s. The authors thank CSIR, New Delhi for financial support as part of XII Five Year Plan under the title ORIGIN (CSC0108).
Notes and references
4460 | Org. Biomol. Chem., 2014, 12, 4454– 4454–4460
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