Fmoc-Glu(OtBu)-OH

Fmoc-Glu(OtBu)-OH

Orthogonal solid-phase synthesis of human gastrin-I under mild conditions.[Pubmed:2401594]

Int J Pept Protein Res. 1990 Jun;35(6):527-38.

An approach to the solid-phase segment condensation synthesis of the 17-peptide amide human gastrin-I has been developed. N alpha-amino and side-chain protection were provided by 9-fluorenylmethyloxycarbonyl (Fmoc) and tert.-butyl groups, and a series of anchors cleavable under mild conditions were used. The N-terminal pentapeptide pGlu-Gly-Pro-Trp-Leu-OH was prepared using a p-alkoxybenzyl ester linkage made by a preformed handle strategy. Cleavage, in 65% yield, was with the new Reagent M: CF3COOH-CH2Cl2-beta-mercaptoethanol--anisole (70:30:2:1), which was optimized to preserve the labile tryptophan residue. A new preformed handle procedure expedited solid-phase synthesis of the protected "middle" hexapeptide, Fmoc-(Glu(OtBu]5-Ala-OH, anchored as an o-nitrobenzyl ester. Chains were not lost during this assembly, and final photolytic cleavage (350 nm) in toluene--CF3CH2OH (4:1) occurred in 59% yield. Both protected intermediates were purified by simple gel filtration, whereupon they were shown to be pure by analytical HPLC, and gave satisfactory NMR and FABMS spectra. Last, the C-terminal hexapeptide, Tyr(tBu)-Gly-Trp-Met-Asp(OtBu)-Phe, was assembled on a tris(alkoxy)benzylamide "PAL" support. For the polymer-supported segment condensation, the middle and N-terminal pieces were added respectively in greater than 98% and 89% yields (judged by amino acid analysis and solid-phase sequencing), by overnight couplings in N,N-dimethylformamide (DMF) mediated by benzotriazolyl N-oxytrisdimethylaminophosphonium hexafluorophosphate (BOP) in the presence of 1-hydroxybenzotriazole (HOBt) and N-methylmorpholine (NMM). Racemization was 4% and 11% respectively at Ala and Leu. Cleavage with Reagent M followed by reversed-phase chromatography gave pure gastrin-I in an overall 30% isolated yield. These results compare favorably with those from a stepwise assembly.

A paclitaxel-conjugated adenovirus vector for targeted drug delivery for tumor therapy.[Pubmed:21959006]

Biomaterials. 2012 Jan;33(1):146-62.

Tumor-targeted drug delivery is an attractive strategy in cancer treatment. Our previous study demonstrated that modified adenovirus has strong tumor targeting ability and less toxicity to surrounding normal tissue. In this study, Paclitaxel (PTX), a widely used clinical anticancer drug, was conjugated to folate-modified adenovirus (Ad) nanoparticles by using succinic anhydride and Fmoc-Glu(OtBu)-OH linkers to form two prodrugs, FA-Ad-Suc-PTX and FA-Ad-ICG02-Glu-PTX. Near-infrared (NIR) fluorescent dye ICG-Der-02 was attached to -NH(2)-Glu(OtBu)-PTX for in vivo optical imaging. In vitro and acute toxicity study demonstrates the low toxicity of the prodrug FA-Ad-Suc-PTX and FA-Ad-ICG02-Glu-PTX compared to the free drug. The dynamic behaviors and targeting ability of FA-Ad-ICG02-Glu-PTX on MDA-MB-231 tumor-bearing mice were investigated by NIR fluorescence imaging. The result show that PTX-conjugated Ad vector could enhance the targeting and residence time in tumor site. In vitro and in vivo studies demonstrate that Coxsackie adenovirus receptor (CAR) or foliate receptor (FR)-mediated uptake of FA-Ad-loaded PTX induced highly anti-tumor activity. The results support the potential of using chemically modified Ad vector as drug-loaded tumor-targeting delivery system.

Synthesis and structural characterization of sialic acid-glutamic acid hybrid foldamers as conformational surrogates of alpha-2,8-linked polysialic acid.[Pubmed:19323529]

J Am Chem Soc. 2009 Apr 22;131(15):5495-505.

Surface expression of alpha-(2,8)-linked polymers of sialic acid in adult tissues has been correlated with metastasis of several human cancers. One approach to chemotherapeutic intervention against the spread of these cancers involves the development of immunogenic molecules that elicit an antibody response against alpha-(2,8)-linked polysialic acids. Naturally occurring polysialic acids are not viable candidates because they are present during embryonic development and are recognized as self by the immune system. These natural polymers also have poor pharmacokinetic properties because they are readily degraded by neuraminidase enzymes. We have been interested in developing structural surrogates of polysialic acids in an effort to overcome these limitations. Reported herein are microwave-assisted solid-phase peptide syntheses and structural characterization studies of a series of alpha/delta hybrid peptides derived from Fmoc-Neu2en and Fmoc-Glu(OtBu)-OH. Conformational experiments including circular dichroism, NH/ND exchange, and ROESY in aqueous solution were performed to study the secondary structures of these hybrid foldamers. ROESY data were analyzed with the assistance of XPLOR-NIH that was modified to include parameter and topology files to accommodate unnatural amino acids and the delta amide linkages. The results indicate that stable secondary structure is dependent upon both the amino acid sequence and the configuration of Glu. The most stable foldamer was composed of a total of 6 residues beginning with L-Glu at the carboxy terminus and alternating Neu2en and L-Glu residues. In water, this foldamer adopts a right-handed helical conformation with 3.7 residues per turn, 7.4 A pitch, 5.8 A diameter, and a length of 18.5 A, which is stabilized by both classical C=O...H-N backbone interactions and by pyranose ring O and L-Glu HN H-bonding. These structural features orient the L-Glu carboxylates along the helical backbone with a periodicity that matches the carboxylate positions along the reported G2(+) left-handed helix of alpha-(2,8)-polysialic acid. However, the charge density of the foldamer is one-half that of the natural polymer. These findings provide a fundamental understanding of the factors that influence stable secondary structure in hybrid Neu2en/Glu systems, and the tools we have developed establish a viable platform for the rational design of alpha-(2,8)-polysialic acid surrogates.