No abstract

The reaction of ring-closing metathesis-derived cyclic allylsiloxanes 3 with aldehydes in the presence of a Lewis acid gives 2,3,4-trisubstituted tetrahydrofurans related to the furanolignan family of natural products. The reactions proceed with complete 3,4-trans stereoselectivity, whereas the C-2 stereochemistry depends on both the aldehyde and Lewis acid used. When boron trifluoride etherate is used with aliphatic or electronically neutral aryl aldehydes, the reactions favor the production of the 2,3-cis isomer 8, whereas electron-rich aryl aldehydes lead to the 2,3-trans isomer 9 by Lewis acid-mediated isomerization of the kinetically favored cis isomer. The isomerization can be avoided by use of TMSOTf as a promoter, and hence, the stereochemistry can be tuned by appropriate choice of reagent. Cleavage of the pendant 3-ethenyl group installs the 3-hydroxymethyl group common to the furanolignans.

The synthesis and phosphodiesterase (PDE) inhibitory profile of a series of imidazopyridines, including sulmazole and isomazole, on separated PDE isoenzymes are described. The results show that both sulmazole and isomazole are weak inhibitors of PDE III, and their inotropic activity is unlikely to be due to PDE III inhibition alone. Surprisingly, both compounds were found to be significant inhibitors of the cGMP specific isoenzyme, PDE V, and a series of simple 2-substituted phenylimidazo[4,5-b]pyridines have been made to investigate the SAR of PDE activity. This has been shown to be sensitive to chain length, polarity, and the nature of the heteroatom linking group. Potent PDE V inhibitors, many of which are also significant inhibitors of PDE IV, have been identified.

No abstract