1. Bioactive gold(i) complexes with 4-mercaptoproline derivatives
Alejandro Gutiérrez, Carlos Cativiela, Antonio Laguna, M Concepción Gimeno Dalton Trans. 2016 Sep 14;45(34):13483-90. doi: 10.1039/c6dt02000c. Epub 2016 Aug 8.
Unprecedented gold(i) bioconjugates bearing non-proteinogenic amino acid 4-mercaptoproline species as bioorganic ligands have been prepared. Firstly, the synthesis of Boc-Pro(SH)-OMe (1) has been accomplished by standard procedures. The subsequent reaction of 1 with [AuCl(PR3)] gives complexes Boc-Pro(SAuPR3)-OMe (PR3 = PPh3 (2), PPh2Py (3)). Starting from complex 2 several structural modifications have been performed, in addition to the incorporation of a different phosphine in 3, such as the formation of the acid Boc-Pro(SAuPPh3)-OH (4), the synthesis of a dipeptide derivative by coupling the amino acid glycine tert-butyl ester Boc-Pro(SAuPPh3)-Gly-O(t)Bu (5), or the coordination of another gold phosphine fragment to the sulfur atom as in [Boc-Pro(SAuPPh3)2-OMe]OTf (6). The cytotoxic activity in vitro of these complexes has been evaluated against three different tumor human cell lines, A549 (lung carcinoma), Jurkat (T-cell leukaemia) and MiaPaca2 (pancreatic carcinoma). All the complexes displayed excellent cytotoxic activity with IC50 values in the low μM range and even in the nM range in some cases. Structure-Activity Relationships (SAR) observed from this family of complexes opens the possibility of designing more potent and selective promising gold(i) anticancer agents.
2. Amino acid-linked porphyrin-nitroimidazole antibiotics targeting Porphyromonas gingivalis
Simon A Dingsdag, Benjamin C-M Yap, Neil Hunter, Maxwell J Crossley Org Biomol Chem. 2015 Jan 7;13(1):98-109. doi: 10.1039/c4ob01841a.
The periodontal pathogen Porphyromonas gingivalis requires porphyrin supplementation for growth. Previously, in order to inhibit P. gingivalis growth, we synthesised very effective 'Trojan horse' ester and amide-linked deuterporphyrin-nitroimidazole (DPIX-Nim) adducts that exploited this requirement to transport metronidazole-derived antibiotics with excellent antimicrobial selectivity and recognition by the HA2 porphyrin binding site. Herein, in the context of developing topical agents to target P. gingivalis, l-amino acids are incorporated into adducts as linkers to improve uptake. Ten 13- and 17-propionic amide regioisomers of l-amino acid-linked deuterporphyrin-nitroimidazole adducts were synthesised using a peptide coupling approach. DPIX-Lys regioisomers without attached nitroimidazole were also synthesised as comparison compounds. All the porphyrin adducts bound (Kd50 7 to 20 nM) to a recombinant HA2 receptor with similar binding affinity to haem, except the lysine-proline linked DPIX-Lys(Boc)Pro-Nim adducts (Kd50 300 nM) and the DPIX-Lys(Nim)-Nim adducts (Kd50 200 nM), both of which have large appended groups. DPIX-Lys(Boc)-Nim, DPIX-Lys(OH)-Nim, and DPIX-Pro-Nim adducts were shown to be very effective against P. gingivalis. DPIX-Lys(Boc)Pro-Nim adducts and DPIX-Lys(Nim)-Nim adducts showed weak activity. Importantly, DPIX-Lys(Boc)-Nim adducts were selective for P. gingivalis and, unlike metronidazole, did not kill a range of other anaerobic bacteria isolated from the human gastrointestinal tract.
3. Synthesis and crystal structures of Boc-L-Asn-L-Pro-OBzl.CH3OH and dehydration side product, Boc-beta-cyano-L-alanine-L-Pro-OBzl
A N Stroup, L B Cole, M M Dhingra, L M Gierasch Int J Pept Protein Res. 1990 Dec;36(6):531-7. doi: 10.1111/j.1399-3011.1990.tb00992.x.
Boc-L-Asn-L-Pro-OBzl: C21H29O6N3.CH3OH, Mr = 419.48 + CH3 OH, monoclinic, P2(1), a = 10.049(1), b = 10.399(2), c = 11.702(1) A, beta = 92.50(1)degrees, V = 1221.7(3) A3, dx = 1.14 g.cm-3, Z = 2, CuK alpha (lambda = 1.54178 A), F(000) = 484 (with solvent), 23 degrees, unique reflections (I greater than 3 sigma(I)) = 1745, R = 0.043, Rw = 0.062, S = 1.66. Boc-beta-cyano-L-alanine-L-Pro-OBzl: C21H27O5N3, Mr = 401.46, orthorhombic, P2(1)2(1)2(1), a = 15.741(3), b = 21.060(3), c = 6.496(3) A, V = 2153(1) A3, dx = 1.24 g.cm-3, Z = 4, CuK alpha (lambda = 1.54178 A), F(000) = 856, 23 degrees, unique reflections (I greater than 3 sigma(I)) = 1573, R = 0.055, Rw = 0.078, S = 1.86. The tert.-butyloxycarbonyl (Boc) protected dipeptide benzyl ester (OBzl), Boc-L-Asn-L-Pro-OBzl, prepared from a mixed anhydride reaction using isobutylchloroformate, Boc-L-asparagine, and HCl.L-proline-OBzl, crystallized with one methanol per asymmetric unit in an extended conformation with the Asn-Pro peptide bond trans. Intermolecular hydrogen bonding occurs between the methanol and the Asn side chain and between the peptide backbone and the Asn side chain. A minor impurity due to the dehydration of the Asn side chain to a beta-CNala crystallized with a similar extended conformation and a single intermolecular hydrogen bond.
