Two Dolabrane-type Diterpenoids

The crystal structures of two dolabrane diterpenes, ent-2-seco-3-nor-5α,4,15-dioxo-16-hydroxydolabran-2-oic acid, C₁₉H₃₀O₅, (I), and ent-2-seco-3-nor-5α,16-chloro-15-hydroxydolabran-2-oic acid, C₁₉H₃₁ClO₄, (II), have been determined at room temperature. They revealed the presence of two trans-fused rings having a chair conformation and they confirmed previous NMR studies showing that the C9 substituent is trans with respect to those at C8 and C10. Furthermore, we observed that the longer C_sp³—C_sp³ distances occor for C9—C10 and C5—C10, which is in agreement with the values found in other diterpenes. These are the first reported crystal structures of dolabrane molecules.

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