Search

In the title compound, racemic bucetin [systematic name: N -(4-eth-oxy-phen-yl)-3-hydroxy-butanamide], C 12 H 17 NO 3 , the mol-ecule is in an extended conformation as illustrated by the C-O-C-C torsion angle [170.14 (15)°] in the eth-oxy group and the subsequent C-N-C-C [-177.24 (16)°], N-C-C-C [170.08 (15)°] and C-C-C-C [171.41 (15)°] torsion angles in the butanamide chain. In the crystal, the O-H group donates an inter-molecular O-H⋯O hydrogen bond to the amide carbonyl oxygen atom and also accepts an inter-molecular N-H⋯O hydrogen bond from an adjacent N-H group. The former forms 12-membered dimeric rings about inversion centers, and the latter form chains in the [001] direction. The overall hydrogen-bonded network is two-dimensional, with no propagation in the [100] direction., (© Hines III et al. 2023.)

Temperature-dependent electric deflection measurements have been performed for a series of unsolvated alanine-based peptides (Ac-WA(n)-NH(2), where Ac = acetyl, W = tryptophan, A = alanine, and n = 3, 5, 10, 13, and 15). The measurements are interpreted using Monte Carlo simulations performed with a parallel tempering algorithm. Despite alanine's high helix propensity in solution, the results suggest that unsolvated Ac-WA(n)-NH(2) peptides with n > 10 adopt beta-sheet conformations at room temperature. Previous studies have shown that protonated alanine-based peptides adopt helical or globular conformations in the gas phase, depending on the location of the charge. Thus, the charge more than anything else controls the structure.

Molecular beam electric deflection measurements have been used to determine electric susceptibilities for small unsolvated alanine-based peptides. The electric susceptibility provides information about the charge distribution within the peptide and can be used to distinguish between zwitterionic and canonical forms. Measured electric susceptibilities for WAn peptides (n = 1-5) are similar to those for capped Ac-WAn-NH2 peptides (which cannot form zwitterions). Susceptibilities calculated using a simulated tempering-based approach are substantially larger for the zwitterionic form than for the canonical form. The measured susceptibilities are in good agreement with those calculated for the canonical form. For the larger peptides, the lowest potential energy structure found in the simulations is hairpin-like, while the lowest free energy structure found at room temperature is extended. The zwitterionic form is constrained by intramolecular interactions which make it entropically unfavorable.

The DC electric susceptibilities of unsolvated glycine-based peptides, WGn (W = tryptophan and G = glycine) with n = 1-5, have been measured by deflection of a molecular beam in an electric field. These are the first electric deflection measurements performed on peptides. At 300 K the susceptibilities are in the range of 200-400 A(3). By far the largest contribution to the susceptibilities is from the permanent dipole moment of the peptides. The results indicate that the peptides do not have rigid conformations with fixed dipoles. Instead the dipole is averaged as the peptides explore their energy landscape. For a given WGn peptide, all molecules have almost the same average dipole, which suggests that they all explore a similar energy landscape on the microsecond time scale of the measurement. The measured susceptibilities are in good overall agreement with values calculated from the average dipole moment deduced from Monte Carlo simulations.

The analysis of hydrophobic and hydrophilic peptides in an aqueous medium using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is reported. The key development allowing for simultaneous analysis of both hydrophobic and hydrophilic components of the sample mixture is the use of surfactants to solubilize the hydrophobic components in the MALDI matrix solution. A wide variety of anionic, cationic, zwitterionic, and nonionic surfactants were evaluated for their ability to assist in the generation of an abundant pseudomolecular ion from a model hydrophobic peptide ([tert-butoxycarbonyl]Glu[gamma-O-benzyl]-Ala-Leu-Ala[O-phenacyl ester]). The results indicate that the most successful surfactant among those studied for analyzing the model hydrophobic peptide is sodium dodecyl sulfate (SDS). SDS exhibited no interfering surfactant background ions, little to no loss of the acid-labile protecting groups from the model hydrophobic peptide, and an abundant pseudomolecular ion of the analyte. In addition, the use of surfactants is shown to be compatible with hydrophilic peptides as well. Mixtures of hydrophobic and hydrophilic peptides were characterized using surfactant-aided (SA) MALDI-MS, and it is demonstrated that all components are detectable once the surfactant is included in the sample solution. We conclude that the key benefit of using SA-MALDI-MS is its ability to simultaneously analyze hydrophobic and hydrophilic peptides from a single sample mixture, including synthetic peptides containing acid- and base-labile protecting groups.

Forty-seven patients with locally invasive thyroid carcinoma were treated at the M.D. Anderson Hospital over a 10 year period. The factors that adversely affected their survival included age, male sex, spindle and giant cell histology, and extensive involvement of adjacent structures in the neck. Surgical treatment aimed at removal of all gross tumor with preservation of vital structures whenever possible offers a reasonable chance of cure in locally aggressive well-differentiated thyroid cancer. Extensive ablative procedures are rarely indicated and do not improve survival. Radioactive iodine is beneficial in the treatment of well-differentiated lesions.