9253-9265 9253 hydrophobic 'backside" of the molecule containing the ~T y r ' and Cys6 side chains. These side chains impart a net hydrophobic moment to the molecule and may directly enhance binding by shielding the arginine and aspartic acid side-chain interactions with GPIIbIIIa from competition due to solvent. Accordingly, substitution of a hydrophilic residue for pTyr2 results in diminishedIn kistrin and echistatin, the bulk of the protein may provide a similar shielding function.Coupling an understanding of the local RGD geometry of 1 with an appropriate placement of hydrophobic groups defines a template for the design of non-peptide antagonists of GPIIb-IIIa-fibrinogen binding. Our construction of that template, and the resulting design efforts, will be reported in the future. Experimental SectionSptbesis. The synthesis and characterization of compounds 1-3 have been described by Barker.20 L-Cysteine (95% IsN) was purchased from Cambridge Isotope Laboratories, Woburn, MA. NMR Measurements. All spectra were recorded on a Varian VXR-300s spectrometer at 293 K unless noted. All samples were 10 mM in water (10% 2H atoms for amide NH detection, 99.9% 2H atoms otherwise) and were adjusted to a pH of 6.8-7.0 with sodium bicarbonate or sodium phosphate. Chemical shifts were measured relative to the HOD signal at 4.85 ppm. The pulse sequences used were supplied within the VNMR software (Varian Associates, release 3.2). Deuterium oxide (99.9% 2H atoms) was purchased from Aldrich.One-dimensional 'H NMR spectra: 90° pulse 10.5 ps, pulse width 3.5 w, 64 acquisitions. The amide temperature coefficient studies were performed at 273-323 K in 2-deg steps from 273 to 293 K and 5-deg steps from 293-323 K. Side-chain resonance coalescence experiments were performed at 293-363 K in 5-deg increments. COSY spectra: relaxation delay 2 s, 90° pulse 10.5 ps, spectral width in bothfl and12 dimensions 3500 Hz.ROESY spectra: relaxation delay 2 s, 90° pulse 10.5 ps, pulse width for spin-lock field 1.8 ps, mixing time 50 ps, spectral width in bothfl and $2 dimensions 3500 Hz. Acknowledgment. We gratefully acknowledge Jeffrey Y. K.Tom, Kathryn S. Chan, and Martin Struble for the synthesis and purification of lb-3b. We would also like to acknowledge and thank Gerhard Wagner for invaluable discussions and advice.Supplementary Material Available: R O S Y spectra of 20 and 3a in water (99.9% 2H atoms), 'H chemical shift tables for 2a and 3a, and coordinates for one of the minimized A-1 structures ( 5 pages). Ordering information is given on any current masthead page.Abstract: Photolysis of the title compound (cisDCBPR) with calf thymus DNA leads to the formation of covalent adducts. The reaction is not dependent on oxygen, proceeds with moderate (ca.quantum efficiency, and occurs with modest enantioselectivity which is enhanced in low ionic strength media, where electrostatic and/or intercalatory association is evident. At least two covalent adducts involving deoxyguanosine as a ligand have been isolated from the enzymatic degradation of the ...

E‐Urocanic acid exhibits a single, featureless, long‐wavelength absorption band with λmax˜258 nm in water. However, the quantum efficiency for E→Z photoisomerization is wavelength dependent in this region, with the maximum value at the low energy edge of the band (e.g. 313 nm) and appreciably lower efficiencies measured at ≦ 300 nm.

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