I wanted to send people to this 50-year retrospective in J. Med. Chem.. It's one of those looks through the literature, trying to see what kinds of compounds have actually been produced by medicinal chemists. The proxy for that set is all the compounds that have appeared in J. Med. Chem. during that time, all 415, 284 of them.
The idea is to survey the field from a longer perspective than some of the other papers in this vein, and from a wider perspective than the papers that have looked at marketed drugs or structures reported as being in the clinic. I'm reproducing the plot for the molecular weights of the compounds, since it's an important measure and representative of one of the trends that shows up. The prominent line is the plot of mean values, and a blue square shows that the mean for that period was statistically different than the 5-year period before it (it's red if it wasn't). The lower dashed line is the median. The dotted line, however, is the mean for actual launched drugs in each period with a grey band for the 95% confidence interval around it.
As a whole, the mean molecular weight of a J. Med. Chem. has gone up by 25% over the 50-year period, with the steeped increase coming in 1990-1994. "Why, that was the golden age of combichem", some of you might be saying, and so it was. Since that period, though, molecular weights have just increased a small amount, and may now be leveling off. Several other measures show similar trends.
Some interesting variations show up: calculated logP, for example, was just sort of bouncing around until 1985 or so. Then from 1990 on, it started a steep increase, and it's hard to tell if that's leveling off or not even now. At any rate, the clogP of the literature compounds has been higher than that of the launched drugs since the mid-1980s. Another point of interest is the fraction of the molecules with tetrahedral carbons. What you find is that "flatness" in the literature compounds held steady until the early 1990s (by which point it was already disconnected from the launched drugs), but since then it's gotten even worse (and further away from the set of actual drugs). This, as the authors speculate, is surely due to metal-catalyzed couplings taking over the world - you can see the effect right in front of you, and so far, the end is not in sight.
Those two measures are the ones moving the most outside the range of marketed drugs. And despite my shot at early combichem molecules, it's also clear that publication delays mean that some of these things were already happening even before that technique became fashionable (although it certainly revved up the trends). Actually, if you want to know When It Changed in medicinal chemistry, you have to go earlier:
It is worth noting that these trends seemed to accelerate in the mid-1980s, indicating that some change took place in the early 1980s. The most likely explanations for an upward change in the early 1980s (before the age of combinatorial chemistry or high-throughput screening) seem to be advances in molecular biology, i.e., understanding of receptor subtypes leading to concerns about speciﬁcity; target-focused drug design and its corresponding one-property-at-a-time optimization paradigm (possibly exacerbated by structural biology); and improvements in technologies which enabled the synthesis and characterization of more complex molecules.
Target-based drug design, again. I'm really starting to wonder about this whole era. And if you'd told me back in, say, 1991 about these doubts that I'd be having, I'd have been completely dumbfounded. But boy, do I ever have them now. . .