Boc-p-alanine

The same findings with respect to reaction time reduction were made for the (3-dipeptide synthesis using pentafluorophenyl O-activation. Boc-[J-alanine was preactivated by introducing the pentafluorophenyl function as ester group [9]. Dmab-(3-alanine and the pentafluorophenyl ester of Boc-P-alanine reacted, and the synthesis of the corresponding P-dipeptide was realized. 

Boc-P-alanine-(4-carbonylaminomethyl)-benzyl-ester-copoly(styrene-divinyl-benzene)resin, (Boc-P-Ala-Pam resin). Optimal loading level of 0.2-0.25 mmol/g (Peptides International, Louisville, KY). 

OS 26] [R 4] [P 18] For dipeptide formation from the pentafluorophenyl ester of Boc-D-alanine and (S)-a-methylbenzylamine an extent of racemization of 5.6% was found [86]. This experiment also served to demonstrate monitoring of the racemization of an a-amino acid used in peptide synthesis. 

Peptide cleavage from the allyl-linker resin is achieved with morpholine in large excess in the presence of tetrakis(triphenylphosphine)palladium (10mol% based on the allylic substitution of the resin). (3-HYCRAM resin is a modification of HYCRAM containing a P-alanine residue as a spacer between the crotonoyl unit and the resin. It has been used for the solid-phase synthesis of glycopeptides by the Boc and Fmoc strategies.b 1 Difficulties may be... 

Peptide formation with an A-protected, optically pure aminocarboxylic acid is an alternative means of obtaining diastereoisomeric derivatives of chiral aminoalkylphos-phonic acids, the diastereoisomeric products being distinguishable on a quantitative basis by P NMR spectroscopy for example, A-boc-L-alanine was used to distinguish the enantiomers of diethyl (a-aminobenzyl)phosphonate. The reaction between an enan-tiomerically enriched sample of 125 (R = H) and L-leucine methyl ester hydrochloride in the presence of DCC was followed by HPLC separation of the l,l- and D,L-peptides 126 (R = H ratio 95.3 4.7), and essentially the same procedure was applied to an analysis of 125 (R = OCH2Ph), as prepared using the bislactim ether procedure (see Section IV. C.2.b) when the final product consisted of a mixture of R,S and S,S diastereoisomers in the ratio 87.4 12.6 ... 

Figure 6. Formation of DDMP and HMF from Amadori compounds heated at 150°C for 10 min. Chromatographic conditions column DEVELOSIL ODS-5 (4.6 mm i.d. x 250 mm), mobile phase H20-MeOH (6 1 v/v), flow rate 0.8 ml/min, UV detection 283 nm, chart speed 5 mm/min. A fructose-P-alanine, B fructose-p-toluid-ine, C fructose-Na-t-Boc-lysine.

The 3 -p-azidobenzoyl ATP is prepared with p-azidobenzoic acid and ATP using carbodiimidazole as a catalyst as indicated above for the esterification of ATP with iV-2-BOC-a-alanine. The reaction mixture is subjected to chromatographic resolution with n-butanol water acetic acid (5 3 2) as solvent. The reaction product has a UV absorption band with an 22/ of 0.37. The material is eluted from the paper with water and found to have absorption peaks at 266 and 285 (sh) nm. Irradiation of the aqueous solution with UV light shifts the 266 nm absorption maximum to 257 nm. The starting p-azidobenzoic acid has a maximum absorption peak at 271 nm which is broadened by UV irradiation. 

Indolinone (—)-154 was transformed into the key imine intermediate (- -)-155 smoothly in just a few step reactions. Treatment of (- -)-155 with A-Boc-L-phenylalanine and p-methoxyphenyl (PMP)-isonitrile at room temperature provided 78% yield of ipeptide (- -)-156 via the stereoselective Ugi three-component reaction. Noteworthily, the isonitrile attacks predominantly on the side opposite the bulky 1,1-dimethylallyl group of imine (+)-155 in the Ugi reaction, which was then transformed into (—)-fmctigenine A 157 in just a few steps. Alternatively, the Ugi reaction of (- -)-155 with A-Boc-D-alanine and isonitrile 158 stereoselectively provided 71% yield of tripeptide (- -)-159, which was then transformed into (—)-5-A-acetylardeemin 160 in just a few steps. 

OS 17] ]R 5] ]P 14] Using continuous flow in an electroosmotic-driven micro reactor gave a quantitative yield of the dipeptide in only 20 min (700 V for both Dmab-y0-alanine and the Boc ester) [88]. Batch synthesis under the same conditions gave only a 40-50% yield [5] (57% in [5]), needing 24 h. 

The reaction of A-Boc protected amino acids alanine (184) and valine (185) with phenyldichlorophosphine in the presence of NEt3 was reported to lead to the clean formation of essentially one compound in each case, the P-chiral, tricoordi-nated, 1,3,2-oxazaphospholidinones 186 and 187 respectively (Scheme 52) [83],... 

The process was also applicable to microwave-assisted reactions. Thus, 140a, 140b, and 140 (R1 = z-Pr, R4 = indol-3-ylmethyl) were prepared in a two-step, one-pot synthesis in yields of 55%, 39%, 20%, and with 70%, 73%, 50% ee, respectively. In the first step anthranilic acid was reacted with the appropriate A-BOC-protected amino acid (glycine, L-alanine, and L-valine, respectively) in the presence of P(OPh)3 and dry pyridine under irradiation at 150 °C for 140a or conventional heating at 55 °C for 140b and 140 (R1 = z-Pr, R4 = indol-3-ylmethyl). In the second step the resulting... 

In 1994 Shea et al. reported the preparation of gel-like imprinted polymers with enantioselective esterolytic activity toward the Boc-D-phenyl-alanine p-nitrophenol ester (28) [19]. The polymers were prepared using a covalent approach, rather than metal complexes or non-covalent interactions, by attaching the catalytic phenol-imidazole unit to the TSA phosphonate via ester linkage (29). The imprinted polymer, containing the catalytic unit (30), showed little selectivity toward the D-enantiomer used for the imprinting. 

Burke. T.R., Jr., Smyth, M.S., Otaka, A., and Roller, P.P., Synthesis of 4-phosphono(difluoromethyl)-D.L-plieiiy I alanine and A-Boc and 7V-Fmoc derivatives suitably protected for sohd-phase synthesis of nonhydrolysable phosphotyrosyl peptide analogues, Tetrahedron Lett., 34, 4125, 1993. 

The vacuum uv CD down to 140 nm has been reported for films of oligopeptides having the general formula Boc-(LX) -OMe, where X = alanine, valine, or norvaline, and n = 2-7 (Balcerski et a/., 1976). Substantial amounts the P conformation are indicated at the trimer level in the alanine series, the hexamer level in the norvaline series, and the heptamer level in the valine series. 

Syntheses of rac-la [8-10], (2 >la [11-13], (S)-la [13], (R)-P-(dimethylphenylsilyl)alanine [12], and (7 )-p-(methyldiphenylsilyl)alanine [12] have already been reported. In addition, the ethyl ester and the A -Fmoc and W-Boc derivatives of (K)-la, as well as renin inhibitory peptides bearing (7 )-la, have been described in the literature [14]. In contrast, germanium-containing a-amino acids have not yet been reported. 

Bode et al. incorporated pairs of guest amino acids X and Y into an alaninic host peptide resulting in a sequence of the type Boc-(L-Ala)2-X-Y-(L-Ala)2-NH-POE. The choice of X and Y referred to results from statistical investi tirms on protdns which indicated different probabilities of the selected pairs to occur in the relevant positions i + 1 (X) and i + 2 (Y) of a p-tum... 

When iV-Boc-alanine (160) reacts with this polymer, 161 is formed (an alanine-loaded polymer). The remainder of the synthesis is essentially a DCC-coupling procedure. When 161 is treated with HCl, the Boc group is removed, and treatment with DCC and IV-Boc-valine leads to 162. This sequence of reactions is repeated, using other protected amino acids, until the desired peptide is prepared. In the example at hand, the final product is gly-pro-ser-ala-ala-his-val-leu-val-ala-P, 163 (P represents the polymer bead). When 163 is treated with HBr and trifluoroacetic acid, the peptide gly-pro-ser-ala-ala-val-leu-val-ala (164) is released from the bead and isolated. The polymer is left behind with bromomethyl fragments (Br-CH2-P), which can be recycled. 

Interestingly, an unsymmetrical bifunctional protonated catalyst was developed by Johnston and Singh to promote the asymmetric aza-Henry reaction of a-alkyl a-nitroesters with iV-Boc imines, providing the corresponding chiral a-substituted syra-a,p-diamino acid derivatives of phenyl alanine in high yields, excellent enantioselectivities of up to 99% ee and moderate to high diastereoselectivities of up to 90% de, as shown in Scheme 3.27. ... 

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