Betidamino acids: versatile and constrained scaffolds for drug discovery.

Abstract

Betidamino acids (a contraction of "beta" position and "amide") are N'-monoacylated (optionally, N'-monoacylated and N-mono-or N,N'-dialkylated) aminoglycine derivatives in which each N'-acyl/alkyl group may mimic naturally occurring amino acid side chains or introduce novel functionalities. Betidamino acids are most conveniently generated on solid supports used for the synthesis of peptides by selective acylation of one of the two amino functions of orthogonally protected aminoglycine(s) to generate the side chain either prior to or after the elongation of the main chain.We have used unresolved Na-tert-butyloxycarbonyl-N'ufluorenylmethoxycarbonyl aminoglycine, and N-(Namethyl)-tert-butyloxycarbonyl-N'afluorenylmethoxycarbonyl aminoglycine as the templates for the introduction of beti- these unnatural scaffolds have been found to have physicochemical, structural, biological, metabolic, and absorptive properties that differ from those of the parent peptides. Because of the limitless number of possible oligomers that can be generated from these modular elements, libraries of peptides and peptidomimetics have been used to fulfill a broad spectrum of needs ranging from the identification of epitopes for antibody binding to the generation of novel bioactive leads.Here we report synthetic pathways to orthogonally protected betidamino acid and methylbetidamino acid scaffolds (N'-monoacylated aminoglycine derivatives) (9) for solid-phase peptide synthesis and their use in the design of bioactive gonadotropin-releasing hormone (GnRH) analogs. The structural preferences of betidamino acids and their corresponding mono-and dimethylated derivatives (as compared to those of amino acids and 3-methyl amino acids) were investigated by using molecular mechanics in combination with a continuum solvation model (10) tert-Butyl-N-methylcarbamate. The compound was synthesized previously by reacting methyl isocyanate with tert-butyl alcohol in the presence of potassium tert-butoxide (12) or bis(tributyltin) tert-butyl peroxide (13). The common disadvantages were harsh conditions, side reactions, and low yield. We reacted di-tert-butyl dicarbonate with methylamine to give an almost quantitative yield. To a 40% methylamine solution in water (155.5 g, 2.0 mol), a solution of di-tert-butyl dicarbonate (218 g, 1.0 mol) in tetrahydrofuran (THF, 300 ml) was added over 1.0 hr with stirring and cooling in an ice bath. The reaction mixture was stirred at room temperature overnight and the solvent was evaporated. The residue was dissolved in ether (1.0 liter) and washed consecutively with water, 5% sodium hydrogen sulfate, water, and saturated sodium chloride. Evaporation of the solvent and fractional distillation of the residue afforded 122.0 g (93.0%) of tert-butyl-Nmethylcarbamate: b.p. 51°C/0.5 mm [literature: 41-45°C/0.1 Abbreviations: bXaa, betidamino acid corresponding to amino acid

Iterative Approach to the Discovery of Novel Degarelix Analogues: Substitutions at Positions 3, 7, and 8. Part II

“…All four analogues are short acting. A similar set of derivatives (7-10) was significantly less potent in vitro, likely due to increased steric hindrance (7,8) and charge distribution (9, 10). Interestingly, 9 (with intermediate duration of action) showed some extended duration of action over 10 (with short duration of action).…”

“…37 Additional analogues (24, 25) with the cyclohexyl substitution and otherwise analogous to 21 and 22 are significantly shorter acting. In 26 and 27, we have two analogues differing by one methyl group on the β-nitrogen of Dap 8 . Whereas both analogues are potent (IC 50 ca.…”

“…Most substitutions are based on acylation of the side chains of dibasic residues of α,β-diaminopropionic acid (Dap) and α,γ-diaminobutyric acid (Dab) as well as ornithine reminiscent to our work on betidamino acids (acylated α,α-diaminoacetic acids or amino-glycines). 8 Finally, the key residues encompassing a β-turn 9 at positions 6, 7 and 8 of degarelix were N α -methylated to confer enzymatic stability, 10 increasing solubility 11 and to induce or disrupt sterical constraints with possible effects on activities.…”

Characterization of Betidamino Acid-Containing Somatostatin and Gonadotropin-Releasing Hormone Analogs with Electrospray Mass Spectrometry and Tandem Mass Spectrometry

“…Peptides were synthesized as described in Jiang et al, 16 Rivier et al 9 and Reubi et al 10 Electrospray spectra and tandem mass (MS/MS) spectra were measured with a Bruker Esquire-LC quadrupole/ion trap mass spectrometer (Bruker Daltonics, Billerica, MA, USA). The instrument was operated in the normal scan resolution mode, which allowed a mass range from m/z 50-2000 (data point intervals of 0.6 m/z and a scan rate of 13,000 m/z s -1 ) unless otherwise specified.…”

“…Such integral compounds include peptoids, 1 azoles, 2 2-isooxazoles, 3 oligosulfones, 4 pyrrolidones, 5 vinylogous backbones, 6 beta-methyl amino acids 7 and amino acids containing pseudo-bonds. 8 Aminoglycine has also been shown to be valuable in this arena in yielding betidamino acids (a contraction of "beta" position and "amide") 9 (see Scheme 1). Using betidamino acids, a peptide backbone can be constructed and then different side chains can subsequently be introduced by acylation, thereby producing a large number of analogs in an efficient manner.…”