Question

4. Cytosporolide A was isolated from a soil fungus collected at high altitude on the Tibetan plateau. The compo und has demonstrated some antibiotic activity against the Gram- positive bacteria. Two structures have been suggested for Cytosporolide A. These are shown as polycyclic compounds 3 and 4 H and 1C NMR chemical shifts of the aromatic group for the isolated compound are provided here. Select the more likely structure for Cytos porolide A using two supportive arguments, one from the 1C NMR data and one from the 'H NMR data. Но OH OH OH но OH но L H H HI OMe Hi OMe он Он 4 Cytosporolide A? 3 Cytosporolide A? or 'H NMR aromatic resonance (CDC I3) 8 13H NMR aromatic resonances (CDCla) 8: 6.3 ppm (s, 1H) 162, 154, 141, 114, 108, 100 ppm

Answer 1

structure 4 Cytosporolide A is preffered

because it contains one aromatic singlet which is possible in both structures

here down field shift for carbonyle carbon of - COOH group present at = 162 ppm

a peak at 162 ppm is due to hydrogen bonding present with - COOH group

hence compound with - cOOH group is the correct structure.