Polyketides are a large group of secondary metabolites which either contain alternating carbonyl groups and methylene groups (-CO-CH2-), or are derived from precursors which contain such alternating groups. Many polyketides are medicinal or exhibit acute toxicity.
You find the formula on the wikipedia page https://en.wikipedia.org/wiki/Pikromycin
Thanks for your response. I got those you mentioned but I was confused about the number of C2 and C3 units (see the attached)
It's easier if you look at the biosynthesis figure of the wikipedia page I linked in the previous post. I went for the linked publication and used the corresponding figure (blue:C3, red: C2)
Thanks a lot Dr. Annemarie Honegger. I found 7C3 and 2 C2 units. Is it correct?
No, you are not correct -look at my previous answer!
If you look at the biosynthesis path I annotated in narbonolide.pdf (wikipedia page figure 1), a C3 unit is added in step 1 and 2, then a C2 unit in step 3, followed by four more C3 units, therefore the narbonolide polyketide ring is derived from six C3 and 1 C2 units.
Then the desoamine deoxyamino sugar unit is added as a whole. This sugar is derived from TDP-glucose (wikipedia page figure 2)
The glucose would come from gluconeogenesis, which produces glucose-6-phosphate from two molecules of glyceraldehyde-3-phosphate or dihydroxyacetone phosphate (the two being interconvertible) , therefore from 2 C3 units.
In your drawing, you missed one of the narbonolide carbons and one of the sugar carbons and instead labelled a c2 and one OH as C3 unit, but as I said, the sugar unit is not part of the polyketide synthesis, but added as a whole
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