Question

One of the crowning achievements of natural products synthesis was Bryostatin 1, published by Professor Gary Keck (University of Utah; Journal of the American Chemical Society,2011, 133, 744-747). The Bryostatins are a family of compounds isolated from aquatic invertebrates known as Bryozoans. The compounds are of interest for a variety of biological effects, including anti-cancer activity and reversing brain damage in rodents.

a. How many ether functional groups are present in Bryostatin 1?

b. Identify the other oxygen-containing functional groups.

c. This is called a macrolide because it contains a large number of atoms in the large ring. How many atoms are in the large ring?

d. How many chiral centers are in this molecule?

e. Using the number of chiral centers you reported in part (d), calculate the number of stereoisomers possible at these chiral centers. (Ignore stereoisomers at double bonds.)

Short answer

a) There are total of three ethers in Byrostatin 1, although there is only one true ether and other two groups called hemiacetal that includes an ether portion, but they are not true ethers.

b) The other oxygen-containing functional groups are indicated in the diagram of Bryostatin 1, five esters and two alcohols.

c) The minimum number of atoms making a continuous path around the large ring is 20.

d) Chiral centers around the main ring are at carbons 4, 6, 8, 10, 12, 16 and 18 plus three more at atoms outside of the main ring indicated by a large dot, that is total of 10 chiral centers.

e) A compound with “n” asymmetric carbon atoms might have as many as 2ⁿ stereoisomers. For 10 chiral centers, 2¹⁰= 1024 possible stereoisomers.

Step-by-step solution

Explanation of part (a):

There are total of three ethers in Byrostatin 1, although there is only one true ether and other two groups called hemiacetal that includes an ether portion, but they are not true ethers.

Ether functional group in bryostatin 1

Explanation of part (b) and (c):

The other oxygen-containing functional groups are indicated in the diagram of Bryostatin 1, five esters and two alcohols. Esters are characterized by a carbon bound to three other atoms, a single bond to carbon, a double bond to oxygen, and single bond to an oxygen.The minimum number of atoms making a continuous path around the large ring is 20 which are numbered in the diagram.

Ester and alcoholic functional groups in bryostatin 1

Explanation of part (d) and (e):

A chiral center is defined as an atom in a molecule that is bonded to four different chemical species, allowing for optical isomerism. Atoms other than carbon can also be chiral centers. Chiral centers around the main ring are at carbons 4, 6, 8, 10, 12, 16 and 18 plus three more at atoms outside of the main ring indicated by a large dot, that is total of 10 chiral centers. A compound with “n” asymmetric carbon atoms might have as many as 2ⁿ stereoisomers. For 10 chiral centers, 2¹⁰ = 1024 possible stereoisomers.

Chiral centers in bryostatin 1