Mechanistic studies on the intramolecular cyclization of O-tosyl phytosphingosines to jaspines

A theoretical study to elucidate the mechanistic aspects involved in the tosylation-cyclization reaction of diastereomeric phytosphingosines 1a-1d to jaspines 4a -4d is presented. The stereochemistry of the starting stereoisomers is crucial for the development of weak interactions, both in the reactants and in the transition states. The analysis of the energy barriers of each elementary reaction is consistent with the observed reluctance of tosylate 2d to undergo cyclization. In addition, the initial tosylation can be identified as the limiting step in cyclizations from 1a and 1b

Sphingosine 1-phosphate regulation of extracellular signal regulated kinase-1/2 in embyronic stem cells

Recent evidence suggests that sphingosine 1-phosphate (S1P) regulates self-renewal of human embryonic stem (ES) cells and differentiation of mouse embryoid bodies (derived from mouse ES cells) to cardiomyocytes. We have investigated the role of S1P in regulating ERK-1/2 signaling in mouse ES cells. In this regard, we found that both mouse ES-D3 and CGR8 cells express S1P1, S1P2, S1P3, and S1P5 but lack S1P4. The treatment of ES cells with S1P induced the activation of ERK-1/2 via a mechanism that was not mediated by S1P1, S1P2, or S1P3. This was based on: (i) the failure of S1P1, S1P2, or S1P3 antagonists to inhibit S1P-stimulated ERK-1/2 activation and (ii) the failure of SEW 2871 (S1P1 receptor agonist) to stimulate ERK-1/2 activation. The treatment of ES cells with phytosphingosine 1-phosphate (phyto-S1P), which we show here is an agonist of the S1P5 receptor, stimulated ERK-1/2 activation. These findings therefore suggest that S1P5 may mediate the effects of S1P in terms of regulating ERK-1/2 signaling in ES cells. The S1P-dependent activation of ERK-1/2 was sensitive to inhibition by pertussis toxin (uncouples the G-protein, Gi from GPCR), bisindolylmaleimide I (PKC inhibitor), and PP2 (c-Src inhibitor), but was not reduced by LY29004 (PI3K inhibitor) suggesting that S1P uses Gi-, PKC-, and c-Src-dependent mechanisms to activate the ERK-1/2 pathway in ES cells