Fmoc-D-valine

The sodium salts of amino acids with hydrophobic fluorenyl methyloxy carbonyl (FMOC) group and short alkyl side chains are found to have surfactant properties. This was ascertained first through visual observation of concentration dependent solution behavior and then confirmed by tensiometry measurements. The critical micelle concentrations (CMCs) for the sodium salts of FMOC-l-valine, FMOC-L-leucine, and FMOC-L-isoleucine have been determined to be ~0.1 M. The sodium salt of FMOC-l-norleucine forms a gel at >0.2 M. Powder X-ray diffraction measurements indicated that these surfactants adopt bilayer structures. Three different chiroptical spectroscopic properties, namely optical rotation, electronic circular dichroism, and vibrational circular dichroism, are presented for these surfactants. The specific rotation is found to exhibit an unprecedented increase with concentration beyond CMC. This observation opens up a new area of research relating the concentration dependent increase in specific rotation to the size and shape of aggregates formed by the surfactants.

A practical, gram-scale synthesis of L-pyrazinylalanine (Paa) is described, utilizing Schöllkopf's D-valine-derived bis-lactim ether chiral auxiliary.

[reaction: see text] A hydroxyethylene isostere of the tripeptide Arg-Gly-Leu, representing an important fragment of a novel cyclic-peptide-based uPA inhibitor, was synthesized in few steps employing as the key step a samarium diiodide promoted coupling of either the 4-thiopyridyl ester of N(alpha)-Fmoc- or N(alpha)-Cbz-protected L-ornithine with the N-acryloyl derivative of L-leucine methyl ester. Epimerization under the coupling conditions at the chiral center in the alpha-position to the ketone was demonstrated not to take place. A stereoselective reduction of the Cbz-protected aminoketone obtained from this radical reaction was promoted by the same single-electron reducing agent in the presence of methanol providing the syn-amino alcohol with a diastereoselectivity of 85:15. With the use of lithium tri-tert-butoxyaluminum hydride in methanol, the corresponding anti-isomer was obtained almost exclusively. Subsequent elaboration of the ornithine moiety in the anti-isomer by introduction of the guanidine group followed by hydrolysis of the C-terminal ester bond and protection of the alcohol as its tert-butyldimethylsilyl ether provided the desired tripeptide mimic.

Recently, an unexpected modified residue, gamma-hydroxy-D-valine (D-Hyv), was identified within ribosomally expressed polypeptide chains of four conopeptides from the venoms of Conus gladiator and Conus mus. To assemble Hyv-containing peptides, we have explored several routes for the synthesis of appropriately functionalized Hyv building blocks. D-Hyv was produced from D-Val by using a variation of the previously published K2PtCl4/CuCl2 oxidative method. Direct synthesis of Boc- or Cbz-D-Hyv lactone proceeded in low yield; additionally, the lactones are too unreactive for solid-phase applications. 9-Borabicyclononane or copper-complexed D-Hyv was prepared and treated with tert-butyldimethylsilyl trifluoromethanesulfonate (TBDMSOTf) to produce D-Hyv(O-TBDMS). The most efficient complex disruption was achieved by Chelex 110 resin (Na+ form) treatment of copper-complexed D-Hyv(O-TBDMS). Reaction of D-Hyv(O-TBDMS) with Fmoc-OSu produced Fmoc-D-Hyv(O-TBDMS) in 26% yield from D-Val.