1. Interactions of (Ala*Ala*Lys*Pro)n and (Lys*Lys*Ser*Pro)n with DNA. Proposed coiled-coil structure of AlgR3 and AlgP from Pseudomonas aeruginosa
V N Medvedkin, E A Permyakov, L V Klimenko, Y V Mitin, N Matsushima, S Nakayama, R H Kretsinger Protein Eng. 1995 Jan;8(1):63-70. doi: 10.1093/protein/8.1.63.
The proteins, AlgR3 and AlgP, are involved in the regulation of alginate synthesis in Pseudomonas. They contain multiple repeats of Ala*Ala*Lys*Pro as do several other proteins that resemble histones. The interactions of synthesis oligopeptides composed of repeated Ala*Ala*Lys*Pro or Lys*Lys*Ser*Pro units with DNA were studied by fluorescence of the Fmoc (9-fluorenylmethyloxycarbonyl) group attached to the N-termini of the peptides. DNA quenching of the Fmoc fluorescence of the peptides was used to estimate the apparent association constants for the interaction of Fmoc(AAKP)nOH (n = 2, 4, 8, 18, 32) and of Fmoc (KKSP)nOH (n = 2, 4, 8, 16, 20, 32) with DNA. The Fmoc(AAKP)nOH peptides bind to DNA only at low ionic strength; the Fmoc(KKSP)n OH peptides interact with DNA at both low (0.05 M KCl) and high (0.2 M KCl) salt. At low ionic strength an increase in the number of the repeat units causes an increase in the apparent association constant up to approximately 2 x 10(6) M-1 for both types of peptides at N congruent to 24. The insertion of an AAKTA unit into the middle of the Fmoc(AAKP)8OH peptide increases its affinity to DNA. We propose a model of (AAKP)n and of its interaction with DNA. The repeat unit consists of a single turn of alpha-helix followed by a bend necessitated by Pro. The resultant coiled-coil forms a right-handed superhelix with 10 AAKPs per repeat distance of approximately 33 A.(ABSTRACT TRUNCATED AT 250 WORDS)
2. Identification of Fmoc-beta-Ala-OH and Fmoc-beta-Ala-amino acid-OH as new impurities in Fmoc-protected amino acid derivatives
E Hlebowicz, A J Andersen, L Andersson, B A Moss J Pept Res. 2005 Jan;65(1):90-7. doi: 10.1111/j.1399-3011.2004.00201.x.
During the manufacture of a proprietary peptide drug substance a new impurity appeared unexpectedly. Investigation of its chemical structure established the impurity as a beta-Ala insertion mutant of the mother peptide. The source of the beta-Ala was identified as contamination of the Fmoc-Ala-OH raw material with Fmoc-beta-Ala-Ala-OH. Further studies also demonstrated the presence of beta-Ala in other Fmoc-amino acids, particularly in Fmoc-Arg(Pbf)-OH. In this case, it was due to the presence of both Fmoc-beta-Ala-OH and Fmoc-beta-Ala-Arg(Pbf)-OH. It is concluded that beta-Ala contamination of Fmoc-amino acid derivatives is a general and hitherto unrecognized problem to suppliers of Fmoc-amino acid derivatives. The beta-Ala is often present as Fmoc-beta-Ala-OH and/or as a dipeptide, Fmoc-beta-Ala-amino acid-OH. In collaboration with the suppliers, new specifications were introduced, recognizing the presence of beta-Ala-related impurities in the raw materials and limiting them to acceptable levels. The implementation of these measures has essentially eliminated beta-Ala contamination as a problem in the manufacture of the drug substance.
3. N-triazinylammonium tetrafluoroborates. A new generation of efficient coupling reagents useful for peptide synthesis
Zbigniew J Kamiński, et al. J Am Chem Soc. 2005 Dec 7;127(48):16912-20. doi: 10.1021/ja054260y.
A new generation of triazine-based coupling reagents (TBCRs), designed according to the concept of "superactive esters", was obtained by treatment of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium (DMTMM) chloride with lithium or silver tetrafluoroborate. The structure of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium tetrafluoroborate was confirmed by X-ray diffraction. Activation of carboxylic acids by using this reagent proceeds via triazine "superactive ester". The coupling reagent was successfully used for the synthesis of Z-, Boc-, and Fmoc-protected dipeptides derived from natural and unnatural sterically hindered amino acids and for fragment condensation, in 80-100% yield and with high enantiomeric purity. The manual SPPS of the ACP(65-74) peptide fragment (H-Val-Gln-Ala-Ala-Ile-Asp-Tyr-Ile-Asn-Gly-OH) proceeded significantly faster than with TBTU or HATU, as well as the automated SPPS of the same fragment gave a purer product than by using TBTU or PyBOP. The reagent was also demonstrated to be efficient in on-resin head-to-tail cyclization of constrained cyclopeptides, in SPPS synthesis of Aib peptides, and in the synthesis of esters from appropriate acids, alcohols, and phenols. The high efficiency and versatility of this new generation of TBCRs confirm, for the first time, the usefulness of the concept of "superactive esters" in rational design of the structure of coupling reagents.
