Fmoc-D-Lys(Me,Boc)-OH

Background: Betulinic acid and betulin are triterpenes with documented cytotoxic properties toward various cell lines. Unfortunately both betulinic acid and its metabolic precursor, betulin, are very poorly soluble in aqueous buffers, thus their bioavailability and bio-distribution are insufficient in terms of medical applications. Objective: To investigate the specific anticancer role of the newly synthesized betulin derivatives in human epidermoid carcinoma cells. Methods: In the present study we synthesized five amino acid esters of betulin. For the synthesis we selected alanine (Boc-l-Ala-OH, negative control) and four basic amino acids - natural lysine (Boc-l-Lys(Boc)-OH) and three its unnatural derivatives (Boc-l-Dap(Boc)-OH, Boc-l-Dab(Boc)-OH, and Boc-l-Orn(Boc)-OH). Boc-protected amino acids were most convenient for the synthesis. All new esters have one (betulin-l-Ala-NH2) or two free amino groups which significantly increase their solubility in water and facilitate their transport through the cell membrane. It is worth noting that the biological activity of new esters of betulin is positive correlated with the length of the side chain of l-amino acid. The highest biological activity displayed compound containing lysine side chain (Lys, -CH2-CH2-CH2-CH2-NH2). Considering the biological activity, other derivatives can be set in the following series: Orn (-CH2-CH2-CH2-NH2)>Dab (-CH2-CH2-NH2)>Dap (-CH2-NH2)>Ala (CH3)>betulin. New betulin esters were tested in normal human keratinocytes (HaCaT) and human epidermoid carcinoma cells (A431). To assess cytotoxicity, MTT test was performed after 24, 48 and 72h of incubation with the test compounds at a concentration range of 0.75-100μM. In case of apoptotic activity, a TUNEL method and comet assay were performed. Additionally expression of caspase-3 and PARP1 was evaluated immunocytochemically. Results: The highest cytotoxicity in cells induced skin cancer new compounds, particularly compound containing a lysine side chain (IC50=7μM) and ornithine (IC50=10μM). The highest number of apoptotic cells was observed in case incubation with compound containing Orn, Dab and Dap side chain. Conclusions: The new betulin ester derivatives display enhanced antitumor activity compared to their non-modified precursors. It is worth emphasizing their specific toxicity against epidermoid carcinoma cells.

Hypothesizing that structural constraints in somatostatin (SRIF) analogues may result in receptor selectivity, and aiming to characterize the bioactive conformation of somatostatin at each of its five receptors, we carried out an N(beta)-methylated aminoglycine (Agl) scan of the octapeptide H-c[Cys(3)-Phe(6)-Phe(7)-dTrp(8)-Lys(9)-Thr(10)-Phe(11)-Cys(14)]-OH (SRIF numbering) (ODT-8) that is potent at all SRIF receptor subtypes (sst's) but sst(1). We found that H-c[Cys-LAgl(N(beta)Me,benzoyl)-Phe-DTrp-Lys-Thr-Phe-Cys]-OH (4), H-c[Cys-Phe-LAgl(N(beta)Me,benzoyl)-Trp-Lys-Thr-Phe-Cys]-OH (6), H-c[Cys-Phe-LAgl(N(beta)Me,benzoyl)-dTrp-Lys-Thr-Phe-Cys]-OH (8), and H-c[DCys-Phe-LAgl(N(beta)Me,benzoyl)-DTrp-Lys-Thr-Phe-Cys]-OH (10) had high affinity (IC(50) = 14.3, 5.4, 5.2, and 3.4 nM, respectively) and selectivity for sst(4) (>50-fold over the other receptors). The l-configuration at positions 7 and 8 (l(7), l(8)) yields greater sst(4) selectivity than the l(7), d(8) configuration (6 versus 8). Peptides with the d(7), l(8) (7) and d(7), d(8) (9) configurations are significantly less potent at all receptors. H-c[Cys-Phe-Phe-DTrp-LAgl(betaAla)-Thr-Phe-Cys]-OH (16), H-c[Cys-Phe-Phe-DTrp-DAgl(betaAla)-Thr-Phe-Cys]-OH (17), and their N(beta)Me derivatives at position 9 (18, 19) were essentially inactive. Potent but less sst(4)-selective were members of the Agl-scan at positions 10, H-c[Cys-Phe-Phe-dTrp-Lys-lAgl(N(beta)Me,HO-Ac)-Phe-Cys]-OH (20, IC(50) = 6.5 nM), and 11, H-c[Cys-Phe-Phe-DTrp-Lys-Thr-LAgl(N(beta)Me,benzoyl)-Cys]-OH (22, IC(50) = 6.9 nM), while the d-configuration at positions 10 (21) and 11 (23) led to reduced affinity. One of our best analogues, 8, is an agonist when tested for its ability to inhibit forskolin-stimulated cAMP accumulation in sst(4)-transfected CCL39 cells (EC(50) = 1.01 nM). All Agl-containing analogues were first synthesized using unresolved Fmoc-Agl(N(beta)Me,Boc)-OH, and the diastereomers were separated using HPLC. Chiral assignment at the Agl-containing residue was subsequently done using enzymatic degradation and by de novo synthesis in the cases of H-c[Cys-Phe-DAgl(N(beta)Me,benzoyl)-DTrp-Lys-Thr-Phe-Cys]-OH (9) and H-c[DCys-Phe-DAgl(N(beta)Me,benzoyl)-DTrp-Lys-Thr-Phe-Cys]-OH (11), starting with the papain-resolved Fmoc-DAgl(Boc). These results suggested that the orientation of side chains at position 6, 7, or 11 with respect to the side chains of residues 8 and 9 may be independently responsible for sst(4) selectivity.

Glycation of α-crystallin is responsible for age- and diabetic-related cataracts, which are the main cause of blindness worldwide. We optimized the method of identification of lysine residues prone to glycation using the combination of LC-MS, isotopic labeling, and modified synthetic peptide standards with the glycated lysine derivative (Fmoc-Lys(i,i-Fru,Boc)-OH). The in vitro glycation of bovine lens α-crystallin was conducted by optimized method with the equimolar mixture of [(12)C6]- and [(13)C6]D-glucose. The in vivo glycation was studied on human lens crystallin. The glycated protein was subjected to proteolysis and analyzed using LC-MS. The results of in vitro and in vivo glycation of α-crystallin reveal a different distribution of the modified lysine residues. More Amadori products were detected as a result of the in vitro reaction due to forced glycation conditions. The developed method allowed us to identify the glycation sites in crystallin from eye lenses obtained from patients suffering from the cataract. We identified K166 in the A chain and K166 in the B chain of α-crystallin as major glycation sites during the in vitro reaction. We found also two in vivo glycated lysine residues: K92 in the B chain and K166 in the A chain, which are known as locations for Amadori products. These modification sites were confirmed by the LC-MS experiment using two synthetic standards. This study demonstrates the applicability of the LC-MS methods combined with the isotopic labeling and synthetic peptide standards for analysis of post-translational modifications in the biological material.