Human-alpha-Calcitonin Gene-Related Peptide (h-alpha-CGRP) is a naturally occurring 37 amino acid vasodilatory neuropeptide amide, ACDTATCVTHRLAGLLSRSGGVVKNNFVPTNVGSKAF, with a disulfide bond between residues 2 and 7. The peptide is found in primary afferent sensory nerves and is widely distributed throughout the central and peripheral nervous systems in the body.1 Structure activity studies of h-alpha-CGRP have shown that the middle and C-terminal part of the peptide allow the formation of the appropriate conformation required for the interaction with the receptor, while the N-terminus is essential for biological activity and onset of signal transduction.
Fluorescent h-alpha-CGRP analogs are useful for investigating the mechanism of action behind (re)uptake of h-alpha-CGRP into the sensory nerve terminals and monitoring trafficking of CGRP receptors. As part of an ongoing study on the mechanism of action behind h-alpha-CGRP-induced vasodilation, we here present an Fmoc strategy for the synthesis of h-alpha-CGRP, and two fluorescent h-alpha-CGRP analogs labelled with 5(6)-carboxyfluorescein (Fluo) at the side-chain of K24 and K35. Pseudoprolins dipeptides were used in position 5–6, 8–9 and 16–17. Following purification by preparative HPLC, concentration-response curves were made with fluorescent CGRP analogues on isolated human subcutaneous arteries. CGRP (fluolysine35) and CGRP (wildtype) showed similar potency (pIC50 = 9.40) while CGRP (fluolysine24) showed approximately 5-fold less potency (pIC50 = 8.72) compared to the potency of CGRP (wildtype). In addition, the untagged analogue CGRP (wildtype) and commercially obtained CGRP (BACHEM) showed almost overlapping concentration-response curves.

1. Sheykhzade M. et al., European Journal of Pharmacology 1998, 351(1): 53-59.


2.Nilsson, C. et al. European Journal of Pharmacology, 2016, 773: 24-31.