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Convergence for the /3-CI model conformer was obtained by constructing, at each cycle, not an extrapolated density matrix, but one representing 0.7 of the previous density matrix and 0.3 of the current density matrix. This is equivalent to applying a damping factor to the change in each array element of 0.3. ( 21) This anomeric energy may be an overestimate for the glycosyl chlorides, since it assumes that the CH3-0-CH2-CI torsion angle is unrestricted and 825 can have the optimum value of 74°. In a pyranose ring, this angle is constrained by the ring closure to be closer to 60°; In the two a glycosyl chlorides for which experimental data are available (see Table III), the C(5)-0(5)-C(1)-CI torsion angles are 68 and 72°.(22) These values represent energy differences between the actual minima and are a refinement of those reported previously (ref 14 and 15), where the standard torsion angles of 60 and 180°g ave energy differences of 3.0 and 2.4 kcal/mol for CH3-0-CH2-0H and CH3-0~CH2-0CH3, respectively.

MRI can be used to noninvasively detect, monitor, and quantify the chronic synovitis and progressive destruction of soft tissue and bone in live AIA rats, thereby improving the ability to evaluate disease progression in this preclinical animal model of rheumatoid arthritis.

Purpose:To evaluate the feasibility of using dynamic contrast-enhanced magnetic resonance imaging (MRI) for assessment of muscle perfusion in a rat model of hind-limb ischemia. Materials and Methods:The acute alteration and chronic recovery in muscle perfusion and perfusion reserve after femoral artery ligation were quantified using the maximum Gd-DTPA uptake rate obtained by a T 1 -weighted gradient-recalled echo sequence. Radionuclide-labeled microsphere blood flow measurements were performed for comparison with the MR perfusion measurement on a separate set of animals.Results: After femoral artery ligation, a significant reduction in resting muscle perfusion was only observed at 1 hour post-ligation during the 28-day follow-up period. Muscle perfusion reserve was severely diminished following the ligation. Despite significant recovery over time, perfusion reserve to the ligated limb reached only 63% of the perfusion capacity in the unaffected limb by 42 days post ligation. A strong correlation (r ϭ 0.86) between MR perfusion and microsphere blood flow measurements was observed for evaluation of relative changes in muscle perfusion. Conclusion:Dynamic contrast-enhanced MRI with Gd-DTPA is useful to assess time-dependent changes in muscle perfusion and perfusion reserve in this hind-limb ischemia model.

Molecular orbital calculations on thyroxine analogs indicate that the minimum energy conformation for 3,5-disubstituted compounds is an important structural feature determining biological activity. The proximal conformation of T3 is predicted to be very slightly (0.2 kcal/mol) more stable than the distal. The representation of the valence electrons of C1, Br, and I with 2s-and 2p-like atomic orbitals appears to give a reasonably satisfactory representation of the electronic structure of these halogen compounds.he thyroid hormones, thyroxine (T4; 1) and 3,5,3'-T triiodothyronine (T3; 2), are necessary for the 1, R , , = R , , = I 2, R r = I ; R , , = H maintenance of normal growth and metabolism in a variety of organisms. 2& Since their isolation and structure elucidation in the first half of this century, many(1) (a) University of California; (b) Information Systems Design.

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The benzanthrins, which were produced by Nocardia lurida, were extracted from the fermentation broth with CH2Cl2. Subsequent purification on Sephadex LH-20 and diolbonded silica gel, followed by countercurrent chromatography, afforded analytically pure benzanthrins A and B. FAB-MS revealed that benzanthrins A and B were isomeric. It was demonstrated through degradative and spectroscopic studies that the benzanthrins were di- Fermentation studies with Nocardia lurida, a known producer of the ristocetins, resulted in the additional production of two new antibiotics, benzanthrins A and B. The discovery, fermentation and antibacterial activity of the benzanthrins is the subject of the preceding paper1). This paper will deal with the isolation, structure determination and antitumor activity of these novel antibiotics. ExperimentalGeneral Procedures NMR spectra were obtained with a General Electric GN 500 MHz spectrometer. The samples were run in CD2Cl2 and referenced on the lock solvent (5.32 ppm). The 2D proton-carbon chemical shift correlation (CSCM) experiment was performed on the GN 500 using a 5 mm C-13 probe and a model 1280 computer. The CSCM pulse sequence employed for the experiment was essentially that of FREEMAN and MORRIS2) modified to deliver a composite 180 degree pulse. Ninety degree pulse widths on the 5 mm C-13 probe were 15 pseconds for carbon and 30 useconds for proton. Fixed delays, delta 1 and delta 2, were set to 3.3 and 1.7 mseconds, respectively, with phase-cycling providing quadrature in both dimensions. The 2D homonuclear J-correlation experiment (COSY)3) was run on the GN 500 spectrometer using the 5 mm H-1 probe. The ninety degree proton pulse for this probe was 12 pseconds. Mass spectra were determined on a Kratos MS-50 spectrometer. High resolution measurements were made at 10,000 resolving power. UV spectra were determined with a Perkin-Elmer Lambda 3B UV/VIS spectrophotometer and IR spectra were measured with a PerkinElmer Model 521 grating spectrometer.