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chemical ID help

Caine

Caine

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what is a bicyclic ketal compound? im reading about some new drugs coming on the market soon and came across this nomenclature and not sure what it is. little help please?
 
I am near positive this would refer to a compound with two attached rings, each with a keto (double-bonded oxygen to carbon) group on each ring. A quick google search brought up molecules that fit that description. But perhaps a real chemist will step in and be more specific.
 
A ketal is what you get when a ketone and an alcohol react

So it goes CH3O-C(CH3)2-OCH3, but what a bicyclic ketal is, I'm not sure...

(EDIT) Better described here (edit)
 
Ketals are where the C=O of a ketone group is effectively hydrated to 2 hydroxy groups (see top reaction). These are unstable and spontaneously dehydrate and revert back to the ketone form. When the hydrogen of the OH groups are replaced by an organic group (CH3, C2H5 etc), it forms a stable adduct (bottom left structure). If the compound containing the C=O group also contains an OH group, it's possible for it to form a cyclic ketal (bottom right structure). This is the method by which ketoses (sugars) such as fructose can form a ring structure allowing them to be combined in chains.

Bicyclic just means two attached rings (one may be a cyclic ketal)
 
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A bicyclic ketal would be made from a compound such as "norbornanone".

Ketals are amost always used a protecting groups although it must be said that some of them have been observed to display bioactivity.

Cyclic acetals are more stable than acyclic adducts because of entropic considerations. The reaction is reversible in the presence of small amounts of water/acid but the adducts are stable in water/base.

I'd like to see some comparing/contrasting the two types of ketal (or acetal) in as far as their stability. You know physical parameters such as enthalpy, entropy, Gibbs free energy etc.

Cyclic acetals only give like 88% yields whereas acyclic acetals should give 100% yield in principle. Possibly a moot point actually, nevermind.
 
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