On the dark energy rest frame and the CMB

Dark energy is usually parametrized as a perfect fluid with negative pressure and a certain equation of state. Besides, it is supposed to interact very weakly with the rest of the components of the universe and, as a consequence, there is no reason to expect it to have the same large-scale rest frame as matter and radiation. Thus, apart from its equation of state $w$ and its energy density $\Omega_{DE}$ one should also consider its velocity as a free parameter to be determined by observations. This velocity defines a cosmological preferred frame, so the universe becomes anisotropic and, therefore, the CMB temperature fluctuations will be affected, modifying mainly the dipole and the quadrupole.Comment: 4 pages. Contribution to the proceedings of Spanish Relativity Meeting 2008, Salamanca, Spain, 15-19 September 200

Isolation, Structural Modification, and HIV Inhibition of Pentacyclic Lupane-Type Triterpenoids from <i>Cassine xylocarpa</i> and <i>Maytenus cuzcoina</i>

As a part of our investigation into new anti-HIV agents, we report herein the isolation, structure elucidation, and biological activity of six new (<b>1</b>–<b>6</b>) and 20 known (<b>7</b>–<b>26</b>) pentacyclic lupane-type triterpenoids from the stem of <i>Cassine xylocarpa</i> and root bark of <i>Maytenus cuzcoina</i>. Their stereostructures were elucidated on the basis of spectroscopic and spectrometric methods, including 1D and 2D NMR techniques. To gain a more complete understanding of the structural requirements for anti-HIV activity, derivatives <b>27</b>–<b>48</b> were prepared by chemical modification of the main secondary metabolites. Sixteen compounds from this series displayed inhibitory effects of human immunodeficiency virus type 1 replication with IC₅₀ values in the micromolar range, highlighting compounds <b>12</b>, <b>38</b>, and <b>42</b> (IC₅₀ 4.08, 4.18, and 1.70 μM, respectively) as the most promising anti-HIV agents