Mass Spectrometry in Structural and Stereochemical Problems. LXV.1 Synthesis and Fragmentation Behavior of 15-Keto Steroids. The Importance of Interatomic Distance in the McLafferty Rearrangement2

Carbonyl-Directed Aliphatic Fluorination: A Special Type of Hydrogen Atom Transfer Beats Out Norrish II

Recently, our group reported that enone and ketone functional groups, upon photoexcitation, can direct site-selective sp³ C-H fluorination in terpenoid derivatives. How this transformation actually occurred remained mysterious, as a significant number of mechanistic possibilities came to mind. Herein, we report a comprehensive study describing the reaction mechanism through kinetic studies, isotope-labeling experiments, ¹⁹F NMR, electrochemical studies, synthetic probes, and computational experiments. To our surprise, the mechanism suggests intermolecular hydrogen atom transfer (HAT) chemistry is at play, rather than classical Norrish hydrogen atom abstraction as initially conceived. What is more, we discovered a unique role for photopromoters such as benzil and related compounds that necessitates their chemical transformation through fluorination in order to be effective. Our findings provide documentation of an unusual form of directed HAT and are of crucial importance for defining the necessary parameters for the development of future methods.

Inhibitors of sterol synthesis. Synthesis and spectral properties of 3 beta-hydroxy-5 alpha-cholestan-15-one and its 17 beta-epimer and their effects on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity

3 beta-Hydroxy-5 alpha-cholestan-15-one (2a) and its 14 beta-epimer 2b were prepared from 3 beta-acetoxy-5 alpha-cholest-8(14)-ene (3). Hydroboration of 3 at 45-50 degrees C gave a mixture of 5 alpha,14 alpha-cholestane-3 beta,15 alpha-diol and 5 alpha,14 beta-cholestane-3 beta,15 beta-diol, which were separated on silica gel as their 3 beta-tert-butyldimethylsilyl ethers 5a and 5b. Oxidation of 5a with pyridinium chlorochromate, followed by desilylation with tetrabutylammonium fluoride gave 2a. Analogous transformations of 5b gave 2b contaminated with 2a. Desilylation of 5b followed by oxidation with pyridinium chlorochromate resulted in a mixture composed mainly of 5 alpha,14 beta-cholestane-3,15-dione and 2b. Successive chromatographic separations on silica gel and reversed phase media gave 2b of high purity. Compound 2a was also prepared by lithium-ammonia reduction of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (96% yield) and by selective reduction of 5 alpha-cholestane-3,15-dione with lithium tri-tert-butoxyaluminum hydride (90% yield). Isomers 2a and 2b were readily epimerized under acidic or basic conditions or under conditions used for gas chromatographic analysis. The purities of 2a and 2b were measured from nuclear magnetic resonance (NMR) spectra; chromatographic methods gave less reliable estimates of purity. NMR data also showed that ring C of the 14 beta sterols is predominantly in a chair conformation. The effects of 2a and 2b on the levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase have been studied in Chinese hamster ovary cells.

Mass spectrometry of ring D hydroxylated 3-methoxy-1,3,5(10)-estratrienes

Mass spectra and fragmentation patterns of the epimeric 17-, 16-, 15- and 14-hydroxy derivatives of 3-methoxy-1,3,5(10)-estratriene are compared. The main fragmentation pathways are differently influenced, depending on the position of the hydroxy group. The different configuration of the hydroxy groups is reflected only in the spectra of the epimeric 15- and 14-hydroxy compounds. Possibilities of mass spectrometric differentiation between the hydroxy-estratrienes are discussed.

Preparation of dehydroepiandrosterone, testosterone and progesterone antigens through 7-carboxymethyl derivatives: characteristics of the antisera to testosterone and progesterone

Dehydroepiandrosterone, testosterone and progesterone 7-carboxymethyl derivatives were prepared: 7 alpha and 7 beta epimers were separated and coupled to bovine serum albumin. Preliminary studies of the antisera induced by these antigens showed that they have high affinity and good specificity.

Antitumor agents: structure--activity relationships in tenulin series

Systematic structural modifications were performed on the natural sesquiterpene lactone tenulin to define those groupings essential to, or significant in, its in vivo antitumor activity. Accordingly, the following tenulin analogs were prepared: dihydrotenulin, 2,3-epoxytenulin, isotenulin, dihydroisotenulin, 2,3-epoxyisotenulin, and tetrahydrodeacetylisotenulin. Both the cyclopentenone and the hemiketal units in tenulin were necessary for high in vivo activity.