Instructor Notes — Chapter 33

Part 6 · advanced · prerequisites: Chapters 4, 8, 32 Suggested time: two sessions, or one long session if §33.1–§33.7 are assigned as pre-reading.

What this chapter is actually for

On the surface it is a techniques chapter — substitutions, rings, staples, fatty acids, polymers, fusions. Do not teach it that way. Taught as a catalog, students leave able to define "PEGylation" and unable to do anything with it.

The chapter's real job is to install one rule and its two consequences:

Engineering solves delivery problems and only delivery problems.

Consequence one: nearly every claim that a modification made a peptide "better" or "stronger" is, under examination, a claim about duration, route, or manufacturability. Consequence two: when a peptide drug fails, it almost never fails at delivery — so the entire toolkit in this chapter is irrelevant to explaining most of Part III's disappointments.

If students leave with the rule and the §33.8 anchor, the individual techniques can be looked up.

The single hardest idea to land

Semaglutide's receptor activity is unchanged from the native hormone.

Nearly every student arrives believing the opposite, and the belief is not stupid — it is the natural inference from "engineered drug outperforms natural hormone in patients." The resolution is that the drug outperforms the hormone because it is present, not because it is stronger. Expect to say this three times in three different ways.

A device that works: ask the room to predict, before you tell them, how much semaglutide's receptor potency was increased to buy a 5,000-fold longer half-life. The guesses cluster around "a lot." The answer — essentially none — lands harder as a correction than as a statement.

Where students reliably go wrong

They treat "protease-resistant" as equivalent to "long-acting." §33.1 exists to prevent this and it still happens. Drill it: a protease-proof peptide that the kidney clears in twenty minutes is a twenty-minute drug.

They read the PEGylation section as a scandal. This is the most common misreading in the chapter, and it is worth confronting directly, because the same reflex will distort how they read every technology transition for the rest of their lives. Case Study 33.2 is built for this.

They over-credit the stapled-peptide cell-penetration claim. The mechanism is appealing and the diagrams are persuasive. Push them to the assay question: how would you know?

They cannot believe Lys34→Arg has no patient benefit. Students search for a hidden pharmacological purpose. There isn't one. Sit in the discomfort; it is where the chapter's best discussion lives.

They confuse modification with formulation. A depot injection and a fatty acid both extend exposure. Only one travels with the molecule.

Practical teaching notes

• Teach §33.8 first if you are short on time. The anchor is self-contained and every earlier section can be introduced retrospectively as "the tool that solved change 1 / change 3."
• Build the four-goal map on the board before assigning §33.1. Students who see the map first read the techniques as answers; students who see the techniques first read the map as a summary.
• Do not let the chemistry become the lesson. Nobody needs to draw a diacid. They need to know that the length of it is a dial and that the dial is set by a clinical decision.
• Pair this chapter with Chapter 32 explicitly. Aib forcing chemical synthesis, and Lys34→Arg forcing regioselectivity, are the two places where manufacturing reaches back into the molecule. If students have not read 32, at least remind them what a batch release involves.
• Flag the ratings' scope carefully. The ✅ on lipidation is a pharmacokinetic claim. Several students will read it as an endorsement of lipidated drugs. The chapter guards against this in the rating's final lines; say it out loud anyway.

Assessment guidance

• quiz.md items 5, 8, and 15 are the discriminating ones. If a student gets those three, they have the chapter.
• In exercises.md, the † items are the ones worth grading with comments. A6, B6, B11, C7, C11, D4, and D9 all reward reasoning over recall and all have more than one defensible answer.
• A good short-answer prompt not in the files: "Name one modification in this chapter that appears to violate the chapter's own rule, and defend either reading." Cyclization-for-affinity and Lys34→Arg-for-manufacturing are both good answers.