Is imidazo[1,5-a]pyridine aromatic?

Hello,

I noticed that the Aromatic Ring Count descriptor considers imidazo[1,5-a]pyridine, c1ncn2ccccc12, not to be fully aromatic (i.e. one aromatic ring and one aliphatic ring).

However, if one 'aromatizes' the structure in MarvinSketch, both rings are shown as aromatic.

Which is correct?

Regards, Tim Ritchie.

Two aromatic rings are provided both by Marvin and TopologyAnalyser for me.

cxcalc -N ih "c1ncn2ccccc12" aromaticRingCount
2

Which version of the software do you use? How can we reproduce the problem?

Interesting. In MarvinSketch 5.2.4 and 5.2.5, if you aromatize the structure first the ring count is 1 aromatic + 1 aliphatic. If you don't aromatize the structure the result is 2 aromatics!

I ran a large number of molecules through cxcalc, and this ring system was classed as 1 aromatic + 1 aliphatic. I'll run some again and check...

Regards, Tim Ritchie.

Further to my last post,

In cxcalc, c1cn2ccccc2n1 gives the output 1 aromatic + 1 aliphatic ring, whereas C1=CN2C=CC=CC2=N1 gives 2 aromatic rings.

Thus it appears that the 'aromatic' SMILES is perceived differently...

Regards, Tim Ritchie.

Hi,

Thank you for the report.

The bug has been fixed in Marvin 5.3 already.

Andras