Incorporation of alpha,beta-dehydrophenylalanine (DeltaPhe) residue in peptides induces folded conformations: beta-turns in short peptides and 3(10)-helices in larger ones. A few exceptions-namely, alpha-helix or flat beta-bend ribbon structures-have also been reported in a few cases. The most favorable conformation of DeltaPhe residues are (phi,psi) approximately (-60 degrees, -30 degrees ), (-60 degrees, 150 degrees ), (80 degrees, 0 degrees ) or their enantiomers. DeltaPhe is an achiral and planar residue. These features have been exploited in designing DeltaPhe zippers and helix-turn-helix motifs. DeltaPhe can be incorporated in both right and left-handed helices. In fact, consecutive occurrence of three or more DeltaPhe amino acids induce left-handed screw sense in peptides containing L-amino acids. Weak interactions involving the DeltaPhe residue play an important role in molecular association. The C--H.O==C hydrogen bond between the DeltaPhe side-chain and backbone carboxyl moiety, pi-pi stacking interactions between DeltaPhe side chains belonging to enantiomeric helices have shown to stabilize folding. The unusual capability of a DeltaPhe ring to form the hub of multicentered interactions namely, a donor in aromatic C--H.pi and C--H.O==C and an acceptor in a CH(3).pi interaction suggests its exploitation in introducing long-range interactions in the folding of supersecondary structures.

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The solution and solid structure of Boc-l-Val-ΔPhe-ΔPhe-ΔPhe-l-Val-OMe, containing three consecutive ΔPhe residues, have been determined by X-ray diffraction, nuclear magnetic resonance, and circular dichroism methods. The crystals grown from aqueous methanol are orthorhombic, space group P212121, a = 11.624(2), b = 17.248(2), c = 21.532 Å, V = 4216 (1) Å3, Z = 4. In the solid state, the peptide exhibits a left-handed 310-helical conformation, in spite of the presence of two l-Val residues. NMR and CD studies in different solvents also support the crystal structure data, suggesting that the solid state structure is maintained in solution as well. This is the first report of a dehydropeptide containing three consecutive ΔPhe residues and exhibiting left-handed 310-helical conformation, which demonstrates the remarkable conformational consequences produced by consecutive occurrence of ΔPhe residues in a peptide.

Medicinal plants are nature's gift to human beings to lead a disease-free, healthy life. They play a vital role in preserving our health. India is one of the most medicoculturally diverse countries in the world, where the medicinal plant sector is part of a time-honored tradition that is respected even today. Medicinal plants are believed to be much safer and proved as elixir in the treatment of various ailments. In our country, more than 2000 medicinal plants are recognized. Polyalthia longifolia cv. pendula (Annonaceae) is native to the drier regions of India and is locally known as “Ashoka” and is commonly cultivated in Pakistan and Sri Lanka. This plant is used as an antipyretic agent in indigenous systems of medicine. Pharmacologic studies on the bark and leaves of this plant show effective antimicrobial activity, cytotoxic function, antiulcer activity, hypoglycemic activity, and hypotensive effect. The present article includes the detailed exploration of pharmacologic properties of P. longifolia in an attempt to provide a direction for further research.