Oxazolone is allowed to react with equimolar solutions of various amino acid esters in a number of solvents. The per cent retention of optical activity in the tripeptide product in each instance was obtained by direct comparisons with the optical rotations of the same tripeptides synthesized by the nonracemizing azide-coupling route. For any given solvent, the least amount of racemization occurs when ethyl glycinate is the attacking nucleophile. The ratio of nucleophilicity to basicity of a particular amino acid ester governs the amount of racemization observed; ethyl glycinate has the most favorable ratio for retention of optical activity. Methyl DL-alaninate shows more racemization, while methyl α-aminoisobutyrate causes complete racemization due to steric hindrance favoring basicity. Solvent plays an important role: toluene (least polar) gives the best retention results, while dioxane (most basic) gives the highest extent of racemization. In addition, oxazolone I reacts with a huge excess of hydrazine hydrate in methanol to give a hydrazide identical to that made by the traditional method from dipeptide ester, with no racemization, explaining why optically pure hydrazides are obtained when esters react with hydrazine hydrate. Hydroxylamine reacts with oxazolone I to give an optically active hydroxamic acid, attributed to the 'α effect' (nucleophiles containing unshared pairs of electrons on the atom attached to the nucleophilic center). Camptothecin (I), an alkaloid with a novel ring system exhibiting potent antileukemic and antitumor activities in animals, has been isolated from the tree Camptotheca acuminata, Nyssaceae. The stem wood was extracted using a standard method with leukemia L1210 assay. Silica gel chromatography of the methanol-insoluble material from the chloroform extract followed by crystallization from methanol-acetonitrile gave camptothecin as pale yellow needles. Its physicochemical properties include: molecular formula C20H16N2O4 (m/e 348.1117, calcd 348.1111), mp 264-267° dec, [α]25D +31.3' (CHCl3-MeOH, 8:2), UV λmax 220, 254, 290, and 370 nm (with respective extinction coefficients), IR νmax 3440 (hydroxy), 1760-1745 (lactone), 1660 (lactam), and 1610, 1585 cm-1 (aromatic C=C), and NMR data (60 Mhertz, CD3SOCD3). Camptothecin does not form stable salts with acids. Derivatives such as acetate (Ia), chloroacetate (Ib), iodoacetate (IC), and chlorocamptothecin (Id) were prepared and characterized. Exhaustive hydrogenation of I in acetic acid with Adams catalyst gave the dodecahydro derivative II (C20H28N2O4, m/e 360). X-ray analysis of camptothecin iodoacetate (IC) (orthorhombic, space group P212121) established its structure, confirming camptothecin has structure I. The absolute configuration was determined by Bijvoet's method based on the anomalous dispersion of the iodine atom. Synthesis of camptothecin and simpler analogs, and studies on structure modification effects on biological activity are ongoing. Hunter and Ludwig have shown that water-soluble imido esters react specifically, under mild conditions, with protein amino groups. Since the resulting amidines have pKa values slightly higher than those of ε-amino groups, amidination does not alter the net charge of the protein in the acid or neutral pH range. Diimido esters might thus provide suitable bifunctional protein reagents for studying interresidue distances in proteins. [14C]Dimethyl adipimidate (I) was prepared from [14C]adiponitrile (synthesized from 1,4-dichlorobutane and [14C]NaCN) with an over-all 85% yield and specific activity of 270,000 dpm/pmole. N,N'-Adipamidinobislysine (II) was prepared by reacting α-N-formyllysine with I, purified by ion-exchange chromatography, and characterized by paper chromatography and amino acid analyzer. Bovine pancreatic ribonuclease A (RNAase) was modified with [14C]I at room temperature in 0.1 M phosphate (pH 10.5). Gel filtration on Sephadex G-75 separated monomers, dimers, and higher aggregates.