New Open‐Chain and Cyclic Tetrapeptides,Consisting of α‐, β2‐, and β3‐Amino‐Acid Residues,as Somatostatin Mimics – A Survey

Cyclo‐β‐tetrapeptides are known to adopt a conformation with an intramolecular transannular hydrogen bond in solution. Analysis of this structure reveals that incorporation of a β²‐amino‐acid residue should lead to mimics of ‘α‐peptidic β‐turns’ (cf. A, B, C ). It is also known that short‐chain mixed β/α‐peptides with appropriate side chains can be used to mimic interactions between α‐peptidic hairpin turns and G protein‐coupled receptors. Based on these facts, we have now prepared a number of cyclic and open‐chain tetrapeptides, 7 – 20 , consisting of α‐, β²‐, and β³‐amino‐acid residues, which bear the side chains of Trp and Lys, and possess backbone configurations such that they should be capable of mimicking somatostatin in its affinity for the human SRIF receptors (hsst_1–5). All peptides were prepared by solid‐phase coupling by the Fmoc strategy. For the cyclic peptides, the three‐dimensional orthogonal methodology (Scheme 3) was employed with best success. The new compounds were characterized by high‐resolution mass spectrometry, NMR and CD spectroscopy, and, in five cases, by a full NMR‐solution‐structure determination (in MeOH or H₂O; Fig. 4). The affinities of the new compounds for the receptors hsst_1–5 were determined by competition with [¹²⁵I]LTT‐SRIF₂₈ or [¹²⁵I] [Tyr¹⁰]‐CST₁₄. In Table 1, the data are listed, together with corresponding values of all β‐ and γ‐peptidic somatostatin/Sandostatin^® mimics measured previously by our groups. Submicromolar affinities have been achieved for most of the human SRIF receptors hsst_1–5. Especially high, specific binding affinities for receptor hsst₄ (which is highly expressed in lung and brain tissue, although still of unknown function!) was observed with some of the β‐peptidic mimics. In view of the fact that numerous peptide‐activated G protein‐coupled receptors (GPCRs) recognize ligands with turn structure (Table 2), the results reported herein are relevant far beyond the realm of somatostatin: many other peptide GPCRs should be ‘reached’ with β‐ and γ‐peptidic mimics as well, and these compounds are proteolytically and metabolically stable, and do not need to be cell‐penetrating for this purpose (Fig. 5).     

Efficient Synthesis and Practical Resolution of 1-(Naphthalen-1-yl)ethanamine,a Key Intermediate for Cinacalcet

An efficient synthesis of 1-(naphthalen-1-yl)ethanamine ( RS -2) and its practical resolution to optically pure (1R)-(naphthalen-1-yl)ethanamine ( R -(+)-2), a key intermediate in the synthesis of cinacalcet hydrochloride (1), is described. The resolution of RS -2 using R-(?)-mandelic acid as a resolving agent in ethanol was established on an industrial scale to give pure R -(+)-2 with >99.8% ee after liberation of the amine from its mandelate salt. An efficient process for the racemization of undesired isomer S -(?)-2 is also provided to maximize the yield of desired enantiomer.     

High energy electron irradiation effects on polystyrene films

The effect of an 8 MeV electron-beam on the structural, optical and dielectric properties of polystyrene films has been investigated respectively by means of Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–VIS) spectroscopy and electrical impedance (LCR) analysis over a radiation dose in the range of 50–250 kGy using a Microtron accelerator. The FTIR spectral analysis shows no change in the overall structure of the irradiated polystyrene films, except a minor change in the intensity of a few peaks in the FTIR spectrum, indicating that polystyrene is resistant to electron-beam irradiation over the range of radiation doses investigated. The optical band gap analysis using the UV–VIS absorption spectra of the polystyrene shows a small decrease in the optical band gap (E _g) and the activation energy with an increase in electron doses. Further, the dielectric measurements over a frequency range of 100 Hz to 1 MHz for the electron-beam-irradiated polystyrene films show that both the dielectric constant and the dielectric loss increase with an increase in electron radiation dose, which may be ascribed to the formation of defect sites in the band gap of polystyrene as a consequence of molecular chain scission in the polymer films upon irradiation.