Archive for December, 2007
Separated at birth…
December 16, 2007Phil Baran (from the pre-prof days) and Scott Baio (’Chachi’ from ‘Happy Days’). The only way I can tell these two apart is that Phil is pictured with KC. I bet if Phil were in high school around the same time I was (circa 1978-1982) he would have been tagged with the nickname ‘Chachi’ like my friend Larry who also bore a striking resemblance to this teen TV star.
Links
December 13, 2007Some Interesting Sites:
CrystalEye ”The aim of the CrystalEye project is to aggregate crystallography from web resources, and to provide methods to easily browse, search, and to keep up to date with the latest published information.”
NIH Training Principles of Clinical Pharmacology ”…a series of lectures that cover much of the scientific basis of the bridging discipline of clinical pharmacology.”
UC DAVIS M.I.N.D. Institute Distinguished Lecture Series Webcasts of the distinguished lecture series concerning primarily Autism research.
December 9, 2007
I have carried out simplified analysis of some recent papers on organocatalysis. The first example comes from a paper from the Jacobsen group (Raheem et al. J. Am. Chem. Soc. 2007, 13404, 10.1021/ja076179w) which describes a “H-bond donor” catalyst that effects an enantioselective Pictect-Spengler type reaction. Jacobsen attributes the selectivity to the substrate-halide-catalyst complex shown on the left. However, leaving the halide out of the complex yields an ion pair or perhaps a covalently bound intermediate as shown on the right. This brings the catalyst and substrate into closer contact than the halide-containing complex.
A ground-state model of the des-halide intermediate appears to work in explaining the enantioselectivity of the reaction as shown in the pictures below. In intermediate I, which leads to the minor enantiomer, the indole ring is not able to cyclize onto the acyliminium ion since it is being blocked by an appendage projecting from the catalyst. In contrast when the catalyst is bound to the other face of the acyliminium ion, as in intermediate II, the indole is free to cyclize which leads to the observed dominant enantiomer. Although Jacobsen indicates that some of their experimental work on the mechanism of catalysis makes the direct interaction of the catalyst with the acyliminium less likely, this intermediate is consistent, at least qualitatively, with the stereoselectivity reported for the paper. I am eager to see more details concerning the mechanism to see if this my interpretation holds up.
Intermediate I
Intermediate II
