Boc-D-valine

Aims: The present investigation is targeted towards the synthesis of a novel analogue of a natural peptide of marine origin. Background: Marine sponges are enriched with bioactive secondary metabolites, especially circu-lar peptides. Heterocycles are established organic compounds with potential biological value. Tak-ing into consideration the bio-properties of heterocycles and marine sponge-derived natural pep-tides, an effort was made for the synthesis of a heterocyclic analogue of a natural cyclopeptide. Objective: A heterocyclic analogue of a sponge-derived proline-containing cyclic peptide, rolloam-ide A, was synthesized by interaction of Boc-protected L-histidinyl-L-prolyl-L-valine and L-prolyl-L-leucyl-L-prolyl-L-isoleucine methyl ester and compared with synthetic rolloamide A with bioac-tivity against bacteria, fungi, and earthworms. Methods: The synthesis of cycloheptapeptide was accomplished employing the liquid phase method. The larger peptide segment was prepared by interaction of Boc-protected L-prolyl-L-leu-cine with L-prolyl-L-isoleucine methyl ester. Similarly, the tripeptide unit was synthesized from Boc-protected L-histidinyl-L-proline with L-valine ester. The linear heptapeptide segment (7) was cyclized by utilizing pentafluorophenyl (pfp) ester, and the structure was elucidated by elemental and spectral (IR, 1H/13C NMR, MS) analysis. The peptide was also screened for diverse bioactivities such as antibacterial, antifungal, and potential against earthworms and cytotoxicity. Results: The novel cyclooligopeptide was synthesized with 84% yield by making use of car-bodiimides. The synthesized cyclopeptide exhibited significant cytotoxicity against two cell lines. In addition, promising antifungal and antihelmintic properties were observed for newly synthesized heterocyclic peptide derivative (8) against dermatophytes and three earthworm species at 6 μg/mL and 2 mg/mL, respectively. Conclusion: Solution-phase technique employing carbodiimide chemistry was established to be promising for synthesizing the cycloheptapeptide derivative (8), and C5H5N was proved to be a better base for heptapeptide circling when compared to N-methylmorpholine and triethylamine.

A catalytic asymmetric arylation of sterically tuned imines with arylboroxines was developed by using N-Boc-l-valine-connected amidomonophosphane rhodium(I) catalyst in n-PrOH. The TMS group used for the steric tuning of imines is convertible to other functionalities that are applicable as a key foothold for the carbon-carbon bond-forming coupling reactions.

The crystal structures of the isovaline (Iva) containing dipeptides, Boc-D-Iva-L-Pro-OBzl and Boc-L-Iva-L-Pro-OBzl, were determined by x-ray diffraction. The diastereomeric peptides were shown to adopt unturned conformations closely similar to each other (phi Iva 52 degrees, psi Iva 46 degrees, phi Pro -65 degrees, and psi Pro 143 degrees for D-Iva-L-Pro sequence and phi Iva 52 degrees, psi Iva 44 degrees, phi Pro -63 degrees, and psi Pro 148 degrees for L-Iva-L-Pro sequence). The Pro ring of each peptide was in C gamma-endo conformation. The unusually large angle CIva-NPro-C delta Pro values (131 degrees in both peptides) were observed, that was due to steric repulsion between the delta-methylene of Pro and the alkyl side chain of Iva residue. These conformations were essentially the same as that of the corresponding alpha-aminoisobutyric acid (Aib)-containing peptide Boc-Aib-L-Pro-OBzl. The result has demonstrated that replacement of either one of the two methyl groups of the Aib residue in Boc-Aib-L-Pro-OBzl with an ethyl group does not cause any significant change in the unturned conformation of the dipeptide.