Several camptothecin derivatives containing a modified hydroxy lactone ring have been synthesized and evaluated for inhibition of topoisomerase I and cytotoxicity to mammalian cells. Each of the groups of the hydroxy lactone moiety, the carbonyl oxygen, the ring lactone oxygen, and the 20-hydroxy group, were shown to be critical for enzyme inhibition. For example the lactol, lactam, thiolactone, and 20-deoxy derivatives did not stabilize the covalent DNA-topoisomerase I complex. With a few exceptions, those compounds that did not inhibit topoisomerase I were not cytotoxic to mammalian cells. Two cytotoxic derivatives that did not inhibit topoisomerase I were shown to produce non-protein-associated DNA single-strand breaks and are likely to have a different mechanism of action. One of these compounds was tested for antitumor activity and was found to be inactive. The present findings, as well as other reports that the hydroxy lactone ring of camptothecin is critical for antitumor activity in vivo, correlate with the structure-activity relationships at the level of topoisomerase I and support the hypothesis that antitumor activity is related to inhibition of this target enzyme.

Water-soluble analogues of the antitumor alkaloid camptothecin (1) were prepared in which aminoalkyl groups were introduced into ring A or B. Most of the analogues were prepared by oxidation of camptothecin to 10-hydroxycamptothecin (2) followed by a Mannich reaction to give N-substituted 9-(aminomethyl)-10-hydroxycamptothecins (4-12) or by subsequent modification of Mannich product 4 (13, 15, 17, 19, 21). Others were obtained by modification of the hydroxyl group of 2 (25,26) or by total synthesis (35,42,43). These analogues, as well as some of their synthetic precursors, were evaluated for inhibition of topoisomerase I, cytotoxicity, and antitumor activity. Although there was not a quantitative correlation between these assays, compounds that inhibited topoisomerase I were also cytotoxic and demonstrated antitumor activity in vivo. Further evaluation of the most active water-soluble analogue led to the selection of 9-[(dimethylamino)methyl]-10-hydroxycamptothecin (4, SK&F 104864) for development as an antitumor agent. In addition to its water solubility, ease of synthesis from natural camptothecin, and high potency, 4 demonstrated broad-spectrum activity in preclinical tumor models and is currently undergoing Phase I clinical trials in cancer patients.

The DNA alkylation and sequence specificity of a group of natural and synthetic pyrrolo- [1,4]benzodiazepines [P(1,4)Bs] were evaluated by using an exonuclease I11 stop assay, and the results were compared with in vitro and in vivo biological potency and antitumor activity. The P(1,4)B antibiotics are potent antitumor agents produced by various Actinomycetes, which are believed to mediate their cytotoxic effects by covalent bonding through N-2 of guanine in the minor groove of DNA. In this article we describe the results of a sensitive DNA alkylation assay using exonuclease I11 which permits both estimation of the extent of DNA modification as well as location of the precise guanines to which the drugs are covalently bound. Using this assay, we have evaluated a series of natural and synthetic compounds of the P(1,4)B class for their ability to bind to DNA and also determined their DNA sequence preference. The compounds included in this study are P(1,4)Bs carrying different substituents in the aromatic ring, having varying degrees of saturation in the five-membered ring, or differing in the stereochemistry a t C-lla. These same compounds were evaluated for in vitro cytotoxic activity against B16 melanoma cells, for potency in vivo in B6D2F1 mice (LDm), and for antitumor activity (ILS,) against P388 leukemia cells. A good correlation was found between extent of DNA alkylation and in vitro and in vivo potency. Furthermore, on the basis of electronic and steric considerations, it was possible to rationalize why those compounds that showed negligible biological activity were unable to bond covalently to DNA. Last, we have determined that the degree of saturation in the five-membered ring of the P(1,4)Bs has a significant effect on the DNA bonding reactivity and biological activity of this class of compounds.

4-[2-(Di-n-propylamino)ethyl]-2(3H)-indolone (1c) (SK&F 101468) is a potent and selective prejunctional dopamine receptor agonist. It caused a dose-related inhibition of the constrictor response to electrical stimulation in the isolated perfused rabbit ear artery (EC50 = 100 nM), and this response was antagonized by (S)-sulpiride (KB = 7 nM). Compound 1c did not stimulate or block dopamine-sensitive adenylate cyclase and did not produce stimulation of the central nervous system in rats. It was prepared from (2-methyl-3-nitrophenyl)acetic acid in a multistep sequence based on the Reissert indole synthesis.

This paper describes the use of primary organic chemistry literature in an honors sophomore-level organic chemistry course. The main goal is to expose students to the primary literature of organic chemistry, demonstrating how they can understand and benefit from using it. The assignment encouraged students to communicate about organic chemistry with colleagues and professors and addresses issues in chemical education such as scientific writing, understanding the scientific process, relating lecture material to the real world, and conducting literature searches. Finally, the assignment complements other courses at the University of Massachusettes at Amherst in the evolution of scientific writing and journal skills for chemistry majors. The student evaluation of this assignment, consisting of surveys, focus groups, and anecdotal comments, were positive and argued for its usefulness and continuation. The details of the evaluative instruments and their results are provided. These include how the students located a suitable primary journal paper, which journals they choose to use, and how we plan to change this course in the future. Although we taught the honors sections of the second-semester sophomore organic chemistry course, we believe this assignment has applicability to the general organic courses.