Syntheses of some α-cyclic tripeptides as potential inhibitors for HMG-CoA Reductase

Proximate composition, peptide characterization and bioactive properties of faba bean blanching water

Faba bean (Vicia faba L.) offers a rich nutritional profile with high protein content and abundant vitamins and minerals. Processing of faba beans for freezing requires blanching, yielding liluva (legume processing water), possibly containing leached macronutrients, with potential for upcycling. Past evidence has shown that legume processing water may be high in protein. Peptides generated from faba bean proteins during processing have been shown to have bioactivity and can, for example, inhibit HMG-CoA reductase. HMG-CoA reductase is rate-limiting in the biosynthesis of cholesterols and high cholesterol increases the risk of cardiovascular diseases. Thus, this study examined the composition of legume blanching water, analysed the peptides resulting from in vitro digestion and assayed HMG-CoA reductase inhibitory activity of liluva from faba beans sourced from two farms in Canterbury, New Zealand. Results showed that the blanching water contained around 1.7 g/100 mL solid content. These solids were approximately 30 % protein, 12 % water-soluble carbohydrates, 4 % dietary fibre, and 0.17 % ash. Mineral analysis showed high levels of potassium in macro minerals and zinc in trace minerals. Free amino acid analysis revealed high levels of arginine, alanine, asparagine, and glutamic acid, and low levels of methionine and tryptophan. Mass spectrometry analysis identified 111 and 72 endogenous peptides in farm 1 and 2 raw samples, respectively. Most of these peptides were derived from tripeptidyl-peptidase II and subtilisin-like protease. To understand potential bioactivity of these peptides, peptides were also analyzed after in vitro digestion. The resulting identified peptides indicated in silico predicted bioactivities such as anti-thrombotic, antioxidative, ACE dipeptidyl peptidase -III and -IV inhibition and HMG-CoA reductase inhibition activities. Further validation of the faba bean blanching water after in vitro digestion demonstrated approximately 67 % inhibition of HMG-CoA reductase activity, suggesting potential hypocholesterolemic properties. These findings suggest that faba bean blanching water may serve as a sustainable and functional ingredient with potential cholesterol-lowering effects in food production.

Three Methods for the Solution Phase Synthesis of Cyclic Peptides

Cyclic peptides, which often exhibit interesting biological properties, can be obtained by macrolactamization of adequately protected linear peptide chains. Because of the remarkable biological properties, methods for the efficient cyclization of peptides are of high interest. We herein describe three different protocols for the cyclization of peptides and depsipeptides via amide bond formation. These methods can, in principal, be applied to any linear peptide chain.

Controversy of Peptide Cyclization from Tripeptide

The present investigation reports an attempt to synthesize naturally occurring α-cyclic tripeptide cyclo(Gly-l-Pro-l-Glu) 1, [cyclo(GPE)], previously isolated from the Ruegeria strain of bacteria with marine sponge Suberites domuncula. Three linear precursors, Boc-GPE(OBn)₂, Boc-PE(OBn)G and Boc-E(OBn)GP, were synthesized using a solution phase peptide coupling protocol. Although cyclo(GPE) 1 was our original target, all precursors were dimerized and cyclized at 0 °C with high dilution to form corresponding α-cyclic hexapeptide, cyclo(GPE(OBn))₂7, which was then converted to cyclic hexapeptide cyclo(GPE)₂2. Cyclization at higher temperature induced racemization and gave cyclic tripeptide cyclo(GP_DE(OBn)) 9. Structure characteristics of the newly synthesized cyclopeptides were determined using ¹H-NMR, ¹³C-NMR and high-resolution mass spectrometry. The chemical shift values of carbonyls of 2 and 7 are larger than 170 ppm, indicating the formation of a cyclic hexapeptide.

Synthesis of chiral nine and twelve-membered cyclic polyamines from natural building blocks

A rational strategy for the facile and efficient cyclization of amino acid-based linear precursors forming nine and twelve-membered cyclic peptidomimetics is reported.

Antitumor and antimicrobial activity of some cyclic tetrapeptides and tripeptides derived from marine bacteria

Marine derived cyclo(Gly-l-Ser-l-Pro-l-Glu) was selected as a lead to evaluate antitumor-antibiotic activity. Histidine was chosen to replace the serine residue to form cyclo(Gly-l-His-l-Pro-l-Glu). Cyclic tetrapeptides (CtetPs) were then synthesized using a solution phase method, and subjected to antitumor and antibiotic assays. The benzyl group protected CtetPs derivatives, showed better activity against antibiotic-resistant Staphylococcus aureus in the range of 60–120 μM. Benzyl group protected CtetPs 3 and 4, exhibited antitumor activity against several cell lines at a concentration of 80–108 μM. However, shortening the size of the ring to the cyclic tripeptide (CtriP) scaffold, cyclo(Gly-l-Ser-l-Pro), cyclo(Ser-l-Pro-l-Glu) and their analogues showed no antibiotic or antitumor activity. This phenomenon can be explained from their backbone structures.