Facile rhenium-peptide conjugate synthesis using a one-pot derived Re(CO)3 reagent

Abstract

We have synthesized two Re(CO)3-modified lysine complexes (1 and 2), where the metal is attached to the amino acid at the Nε position, via a one-pot Schiff base formation reaction. These compounds can be used in the solid phase synthesis of peptides, and to date we have produced four conjugate systems incorporating neurotensin, bombesin, leutenizing hormone releasing hormone, and a nuclear localization sequence. We observed uptake into human umbilical vascular endothelial cells as well as differential uptake depending on peptide sequence identity, as characterized by fluorescence and rhenium elemental analysis.

Fig. 1

Structures of Re(CO)₃ conjugates with a neurotensin fragment (3), a nuclear localization sequence (RRRC, NLS, 4), a bombesin fragment (5), and a lutenizing hormone releasing hormone fragment (LHRH, 6).

Fig.2

The chromatograms of 4 (100% A → 100% B in 25 min): 19 min, 5 (100% A → 100% B in 30 min): 25 min, and 6 (100% A → 100% B in 32 min): 25 min with the MALDI-TOF spectra. (Chromatograms: blue trace: 280 nm, red trace : 254 nm detection)

Fig. 3

FT-IR and UV-visible spectra of compounds 1, 2 and 4–6

Fig. 4

Fluorescent micrographs of HUVECs incubated with 40 μM of compound 4 (first row), 5 (second row), and 6 (third row) for 24 hours. Images were achieved in GFP (a), DAPI (b), and merged (c) modes.

Scheme 1

Top: General scheme for a one pot pyca Schiff base Re(CO)₃X reaction. Bottom: Preparation of 1 and 2.

Scheme 2

Synthesis of peptide conjugates 3–6 where amides were formed using the HOBT/HBTU method and cleaved from the resin using TFA: i. Fmoc-deprotection, ii. Washing, iii. Coupling, iv. Repeat washing, v. TFA Cleavage.