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Boc protection with

Hydroxylysine (328) was synthesized by chemoselective reaction of (Z)-4-acet-oxy-2-butenyl methyl carbonate (325) with two different nucleophiles first with At,(9-Boc-protected hydroxylamine (326) under neutral conditions and then with methyl (diphenylmethyleneamino)acetate (327) in the presence of BSA[202]. The primary allylic amine 331 is prepared by the highly selective monoallylation of 4,4 -dimethoxybenzhydrylamine (329). Deprotection of the allylated secondary amine 330 with 80% formic acid affords the primary ally-lamine 331. The reaction was applied to the total synthesis of gabaculine 332(203]. [Pg.334]

The actual process of solid phase peptide synthesis outlined m Figure 27 15 begins with the attachment of the C terminal ammo acid to the chloromethylated polymer m step 1 Nucleophilic substitution by the carboxylate anion of an N Boc protected C terminal... [Pg.1141]

Step 2 The Boc protecting group is removed by treatment with hydrochloric acid m dilute acetic acid After the resin has been washed the C terminal ammo acid IS ready for coupling... [Pg.1143]

Protect glycine as its Boc derivative and anchor this to the solid support Remove the pro tecting group and treat with Boc protected phenylalanine and DCCI Remove the Boc group with HCl then treat with HBr in tnfluoroacetic acid to cleave Phe Gly from the solid support... [Pg.1255]

The trityl group was introduced on a primary amide, RCONH2, in the presence of a secondary amide with TrOH, AC2O, H2SO4, AcOH, 60°, 75% yield. It is stable to BOC removal with 1 N HCl in 50% isopropyl alcohol, 30 min, 50°, but can be cleaved with TFA. The following table gives the cleavage rates with TFA for a number of protected primary amides. [Pg.642]

In 2000, an efficient three-step procedure for the synthesis of 5-substituted 3-isoxazolols (without formation of undesired 5-isoxazolone byproduct) was published. The method uses an activated carboxylic acid derivative to acylate Meldrum s acid, which is treated with A,0-bis(ten-butoxycarbonyl)hydroxylamine to provide the N,0-di-Boc-protected P-keto hydroxamic acids 14. Cyclization to the corresponding 5-substituted 3-isoxazolols 15 occurs upon treatment with hydrochloric acid in 76-99% yield. [Pg.221]

The Henegar modification of the Friedlander reaction has been recently reported. The A-Boc protected derivative of o-aminobenzaldehyde (25, in this case prepared via directed ortho metallation of 24) is a stable, crystalline compound that can be stored for extended periods (in contrast with 4, which typically is freshly prepared). Treatment of 25 with ketone 26 in acetic acid results in deprotection of the aniline in situ and subsequent formation of 27, an intermediate in the synthesis of mappicine. [Pg.413]

The feasibility of this approach was demonstrated with a model library of 36 compounds prepared from a combination of three Boc protected L-amino acids (valine 23, phenylalanine 24, and proline 25) and 12 aromatic amines (3,4,5-trimethoxyaniline (26), 3,5-dimethylaniline (27), 3-benyloxyaniline (28), 5-aminoindane (29), 4-tert-butylamline (30), 4-biphenylamine (31), 1-3-benyloxyani-line (28), 5-aminoindane (29), 4-tert-butylaniline (30), 4-biphenylamine (31), 1-aminonaphthalene (32), 4-tritylaniline (33), 2-aminoanthracene (34),... [Pg.86]

Amino groups are often protected as their tert-butoxycarbonvl amide, or Boc, derivatives. The Boc protecting group is introduced by reaction of the amino acid with di-fert-butyl dicarbonate in a nucleophilic acyl substitution reaction and is removed by brief treatment with a strong organic acid such as trifluoro-acetic acid, CF3C02H. [Pg.1034]

A second Boc-protected amino acid is coupled to the first by reaction with DCC. Excess reagents are removed by washing them from the insoluble polymer. [Pg.1037]

Two recent reports described addition of nitrogen-centered nucleophiles in usefully protected fonn. Jacobsen reported that N-Boc-protected sulfonamides undergo poorly selective (salen) Co-catalyzed addition to racemic epoxides. However, by performing a one-pot, indirect kinetic resolution with water first (HKR, vide infra, Table 7.1) and then sulfonamide, it was possible to obtain highly enantiomer-ically enriched addition products (Scheme 7.39) [71]. These products were transformed into enantioenriched terminal aziridines in straightforward manner. [Pg.254]

Good to excellent diastereoselectivities have been reported when 2-(trimethylsilyl)thiazole (3), an effective equivalent of an aldehyde group, is used as nucleophile24,27. Thus, addition to TV-Boc-protected amino aldehydes in dichloromethane at — 30 C afforded mixtures of amino alcohols in comparatively good yields with reasonable syn selectivity. However, the stereoselectivity decreased substantially when the reaction was carried out in tetrahydrofuran at 25 °C. [Pg.87]

The use of diamine 27, bearing a fluorous-Boc protecting group, has been used with microwave irradiation in an Ugi/de-Boc/cyclization strategy for the synthesis of benzimidazoles 28 and quinoxalinones 29 [64]. Compared to the original procedures, which take 1-2 days, this approach avoids the use of... [Pg.40]

In their search for new hgands with a very high binding affinity for the nicotinic acetylchohne receptor (nAChR), potentially useful in positron emission tomography (PET) when radiolabeled with [ F], Horti et al. described the synthesis of BOC-protected 5-(azetidin-2-ylmethoxy)-2-chloro-6 -fluoro-3,3 -bipyridine via a sequential classical heating and microwave irradiation of (2-fluoro-5-pyridinyl)(trimethyl)stannane with f-butyl 2- [(6-chloro-5-... [Pg.161]

Recently the use of the boron trifluoride catalysed reaction in the synthesis of the oxazolylindole fragment 25 of the natural product diazonamide A has been reported.<96SL609> Thus the BF3-mediated reaction of the indolyl diazoketoester with acetonitrile gave oxazole 25 with simultaneous removal of the Boc-protecting group (Scheme... [Pg.8]

A facile procedure for the synthesis of fcispolyazamacrocycles by the condensation of iV,A -di-BOC protected triazamacrocycles or iV,iV ,lV -tri-BOC protected tetraaza-macrocycles with aromatic feiselectrophiles was reported the BOC protection is readily removed by the treatment with acid <96BSC(Fr)65>. Treatment of 1,5,9-... [Pg.336]

Although these Boc derivatives underwent methylation with poor selectivity (compared to 3-amino-N-benzoyl butanoates [106] and Z-protected methyl 4-phen-yl-3-aminobutanoate [107]), epimers were succesfully separated by preparative HPLC or by flash chromatography. However, saponification of the methyl ester caused partial epimerization of the a-stereocenter and a two-step (epimerization free) procedure involving titanate-mediated transesterification to the corresponding benzyl esters and hydrogenation was used instead to recover the required Boc-y9 -amino acids in enantiomerically pure form [104, 105]. N-Boc-protected amino acids 19 and 20 for incorporation into water-soluble /9-peptides were pre-... [Pg.42]

Enantiopure (R)- and (S)-nipecotic acid (Nip) derivatives 64 were obtained following classical resolution of ethyl nipecotate with either enantiomer of tartaric acid and successive recrystallization of the corresponding salts [153, 154, 156] or by resolution of racemic nipecotic acid with enantiomerically pure camphorsul-fonic acid [154]. N-Boc protected pyrrolidine-3-carboxylic acid (PCA) 65 for the synthesis of homo-ohgomers [155] was prepared by GeUman from trans-4-hydroxy-L-prohne according to a known procedure [157]. [Pg.49]

A similar sequence of 12- and 10-membered turns is present in the structure of Boc-protected /S //S -peptides 96 and 97, the C=0 of the Boc group being engaged in the first 12-membered ring with NH of residue 3. The pattern of 10- and 12-membered turns is reversed for the fully protected / // -peptide 94 as well as the unprotected /S //S -dodecapeptide 98 which thus folds into a 10/12-helix, with the NH of residues 1 and 2, respectively being involved in the formation of an N-ter-minal 10-membered turn. [Pg.66]

Overall yields from Boc-a-amino acids are between 40 and 70% depending on the method and the R side-chain [200, 225], Although feasible, the double Arndt-Eistert homologation of Boc-protected a-amino acids proved unsatisfactory with only low yields of y-amino acids 124 (<20% over five steps) [200] (for previous studies with Z- and phfhalyl- protected a-amino acids, see [226, 227]). [Pg.84]


See other pages where Boc protection with is mentioned: [Pg.445]    [Pg.51]    [Pg.97]    [Pg.96]    [Pg.209]    [Pg.393]    [Pg.138]    [Pg.445]    [Pg.51]    [Pg.97]    [Pg.96]    [Pg.209]    [Pg.393]    [Pg.138]    [Pg.326]    [Pg.100]    [Pg.1142]    [Pg.65]    [Pg.1142]    [Pg.282]    [Pg.620]    [Pg.193]    [Pg.86]    [Pg.1036]    [Pg.601]    [Pg.95]    [Pg.317]    [Pg.12]    [Pg.41]    [Pg.115]    [Pg.35]    [Pg.105]    [Pg.48]    [Pg.84]    [Pg.87]   
See also in sourсe #XX -- [ Pg.174 , Pg.207 , Pg.265 ]




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