The authors found that 35.7% of the 33 million organic compounds ever reported in the chemical literature have one of just 30 framework shapes. Also, 32.3% have one of the top 20 shapes and 26.1% have one of the top 10 shapes. So over a quarter of all the compounds ever reported in the chemical literature have one of 10 different shapes.
What the hell is a framework shape? Well, each of the 30 structures above is one framework shape. Each carbon atom can be substituted for any other heteroatom and each bond can be single, double, or triple. Also, all side chains are ignored. So scaffold 1 encompasses not only cyclohexane, but also piperidine, benzene, pyridine, morpholine, toluene, phenol, 2,6-lutidine, etc. No wonder 2.3 million compounds have that framework shape.
So all you chemists out there, get off your asses and start making some new structures.