Question

graues Support This course Jeremiah Virginiamycin S1 is a member of the streptogramin B group of antibiotics, which bind the peptide exit tunnel to inhibit the elongation stage of translation. How many stereogenic chiral carbon centers do we have in the structure of Virginiamycin S1 shown below? HN HNT ONHO Select one: Ca. 7 O b. 11 f. 10 9.8

Answer 1

Viriginiamycin S1 has 12 chiral carbons.

110 HO NH 2. 6 N 7

The correct answer is OPTION c (12)

The correct answer is OPTION b (carbocation c)

Stability of carbocation • Carbocation is sp2 hybridized & has trigonal planar geometry • Alkyl groups (electron donating groups, +I effect) stabilize carbocations. • Hyper conjugation explains the relative stabilities of carbocations • It stabilizes through donation of the electrons in C-H sigma bonds to the empty p orbital of the carbocation. • The more the number of alkyl groups, more is the number of a C-HO bonds; tertiary (9 hyperconjugatable Hs), secondary (6), primary (3) & methyl (no) • The stability follows the order: Benzylic >> allylid >>tertiary >secondary> primary > methyl Benzylic (resonance stabilized) >> allylic (resonance stabilized) (a). secondary carbocation (b). tertiary carbocation (c). primary carbocation (least stable) (d). secondary carbocation