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11
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12744273171
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Mennen S.M., Blank J.T., Tran-Dube M.B., Imbriglio J.E., and Miller S.J. Chem. Commun. (2005) 195-197
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(2005)
Chem. Commun.
, pp. 195-197
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Mennen, S.M.1
Blank, J.T.2
Tran-Dube, M.B.3
Imbriglio, J.E.4
Miller, S.J.5
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16
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33750469620
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For recent ketone-based enantioselective MBH reactions, see:
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26
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0036134467
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The Shi laboratory reported imidazole in the presence of proline as a co-catalyst (30 mol % each), which afforded enhanced reactivity in the MVK-MBH reaction. Yields of up to 90% were obtained for a variety of activated aldehydes. See:
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The Shi laboratory reported imidazole in the presence of proline as a co-catalyst (30 mol % each), which afforded enhanced reactivity in the MVK-MBH reaction. Yields of up to 90% were obtained for a variety of activated aldehydes. See:. Shi M., Jiang J.-K., and Li C.-Q. Tetrahedron Lett. 43 (2002) 127-130
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(2002)
Tetrahedron Lett.
, vol.43
, pp. 127-130
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Shi, M.1
Jiang, J.-K.2
Li, C.-Q.3
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27
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33750436509
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Proline has been shown to be an efficient and selective catalyst for a number of transformations. For reviews covering this chemistry, see the following and references therein:
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29
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0034750244
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List B. Synlett (2001) 1675-1686
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(2001)
Synlett
, pp. 1675-1686
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List, B.1
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30
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0037043180
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List B. Tetrahedron 58 (2002) 5573-5590
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(2002)
Tetrahedron
, vol.58
, pp. 5573-5590
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List, B.1
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34
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0035838880
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The sequences for the unbiased peptide libraries were defined randomly by assigning a numerical descriptor (1-16) to each of 16 unique amino acids. These 16 labels were then randomized at 'www.randomizer.org' using a random sequence generator. The random pentapeptide libraries were initially synthesized for the kinetic resolution of tertiary alcohols and previously characterized by MS and reported elsewhere. See:
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The sequences for the unbiased peptide libraries were defined randomly by assigning a numerical descriptor (1-16) to each of 16 unique amino acids. These 16 labels were then randomized at 'www.randomizer.org' using a random sequence generator. The random pentapeptide libraries were initially synthesized for the kinetic resolution of tertiary alcohols and previously characterized by MS and reported elsewhere. See:. Jarvo E.R., Evans C.A., Copeland G.T., and Miller S.J. J. Org. Chem. 66 (2001) 5522-5527
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(2001)
J. Org. Chem.
, vol.66
, pp. 5522-5527
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Jarvo, E.R.1
Evans, C.A.2
Copeland, G.T.3
Miller, S.J.4
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35
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33750449255
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note
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3. The reactions were stirred at room temperature for 16 h followed by purification and screening for enantioselectivity by chiral HPLC.
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36
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33750468246
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For studies that describe the conformational biasing prowess of Aib, see:
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37
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33750491032
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Ref. 13
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39
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33750448567
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note
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Because peptides 3 and 4 exhibited identical sequences at the positions i through i+2, we chose these peptides to begin SAR studies.
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40
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33750428138
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note
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3) as solvent provided enhanced enantioselectivity.
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41
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33750465771
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For reviews on combinatorial catalyst screening, see the following papers and references therein:
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47
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33750428874
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note
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Previous studies in our laboratory have demonstrated that focused libraries based on initial hit peptide structures can lead to more selective peptide sequences. See Ref. 2b.
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48
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33750449942
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note
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The synthesis of each peptide sequence was confirmed by MS analysis and crude peptides were then screened in the MBH reaction.
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49
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33750459628
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note
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We recognize that this decision assumes the peptide sequence thus far is optimal at each amino acid position, and therefore, this decision does not take into account cooperativity of the different amino acids.
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50
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33750432417
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note
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We also synthesized peptides of shorter length, catalysts 12-15, to determine if the length-selectivity trend would be apparent with smaller peptides. Shorter peptide lengths such as dipeptide 13, tripeptide 14, and tetrapeptide 15 did appear to follow this trend with the limited number of cases examined.
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51
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33750474004
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note
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A brief study of the peptide/proline ratio revealed that 1:1 stoichiometry is optimal in the cases we explored.
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52
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33750429882
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note
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3 yielded similar selectivities of 78% ee in the MBH reaction of 2-nitrobenzaldehyde with peptide 18.
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53
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33750461192
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note
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3 (2:1) solvent mixtures.
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54
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17844379719
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For a review addressing the reversal of stereochemistry in enantioselective reactions, see:
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For a review addressing the reversal of stereochemistry in enantioselective reactions, see:. Sibi M.P., and Liu M. Curr. Org. Chem. 5 (2001) 719-755
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(2001)
Curr. Org. Chem.
, vol.5
, pp. 719-755
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Sibi, M.P.1
Liu, M.2
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55
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0021775497
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We note that the nonadditivity of the single components of the co-catalysts system suggests that the cooperativity among chiral species is nonclassical in the sense of double stereodifferentiation. See:
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We note that the nonadditivity of the single components of the co-catalysts system suggests that the cooperativity among chiral species is nonclassical in the sense of double stereodifferentiation. See:. Masamune S., Choy W., Petersen J.S., and Sita L.R. Angew. Chem., Int. Ed. Engl. 97 (1985) 1-31
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(1985)
Angew. Chem., Int. Ed. Engl.
, vol.97
, pp. 1-31
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Masamune, S.1
Choy, W.2
Petersen, J.S.3
Sita, L.R.4
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56
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33750431304
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N-Methyl amino acids were synthesized according to the following procedure. See:
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59
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37049079179
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The Li and Na-salts were prepared by mixing proline with either LiOH or NaOH in methanol for 10 min as reported in:
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The Li and Na-salts were prepared by mixing proline with either LiOH or NaOH in methanol for 10 min as reported in:. Yamaguchi M., Yokota N., and Minami T. J. Chem. Soc., Chem. Commun. (1991) 1088-1089
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(1991)
J. Chem. Soc., Chem. Commun.
, pp. 1088-1089
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Yamaguchi, M.1
Yokota, N.2
Minami, T.3
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60
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33750473288
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For the preparation of 5-substituted proline derivatives, see:
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63
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33750452227
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note
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Proline has been shown to serve as a catalyst for a variety of catalytic asymmetric reactions. See Ref. 12.
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68
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33750444861
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For some important recent work on the mechanism of acrylate-based variants of the MBH reaction, see:
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73
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33750460174
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Chloroform was washed with concentrated sulfuric acid (5×5 mL) followed by washing with water (5×5 mL), dried over potassium carbonate, and distilled under nitrogen. See: Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory Chemicals, 4th ed.; Butterworth and Heinemann: Oxford, 1997; p 143.
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74
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33750472257
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note
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1H NMR.
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