Stephen G. Spanton

Ritonavir: An Extraordinary Example of Conformational Polymorphism

AbstractPurpose. In the summer of 1998, Norvir semi-solid capsules supplies were threatened as a result of a new much less soluble crystal form of ritonavir. This report provides characterization of the two polymorphs and the structures and hydrogen bonding network for each form. Methods. Ritonavir polymorphism was investigated using solid state spectroscopy and microscopy techniques including solid state NMR, Near Infrared Spectroscopy, powder X-ray Diffraction and Single crystal X-ray. A sensitive seed detection test was developed. Results. Ritonavir polymorphs were thoroughly characterized and the structures determined. An unusual conformation was found for form II that results in a strong hydrogen bonding network A possible mechanism for heterogeneous nucleation of form II was investigated. Conclusions. Ritonavir was found to exhibit conformational polymorphism with two unique crystal lattices having significantly different solubility properties. Although the polymorph (form II) corresponding to the “cis” conformation is a more stable packing arrangement, nucleation, even in the presence of form II seeds, is energetically unfavored except in highly supersaturated solutions. The coincidence of a highly supersaturated solution and a probable heterogeneous nucleation by a degradation product resulted in the sudden appearance of the more stable form II polymorph.

(±)-Dioxolane-T ((±)-1-[(2β,4β)-2-(hydroxymethyl)-4-dioxolanyl]thymine). A new 2′,3′-dideoxynucleoside prototype with in vitro activity against HIV

Abstract A novel analogue of 3′-deoxythymidine, in which the 3′-carbon is replaced by oxygen, was synthesized in 5 steps from benzyloxyacetaldehyde dimethyl acetal and (±)-methyl glycerate. In ATH8 cells, this analogue showed significant inhibition of the infectivity and cytopathic effect of HIV at a concentration of 20 uM, while the growth of the uninfected control cells was not affected by concentrations as high as 200 uM. X-ray crystallographic analysis confirmed the assignment of stereochemistry and established a3T4 type conformation of the dioxolane ring.

A quantitation method for mass spectrometry imaging

A new quantitation method for mass spectrometry imaging (MSI) with matrix-assisted laser desorption/ionization (MALDI) has been developed. In this method, drug concentrations were determined by tissue homogenization of five 10 µm tissue sections adjacent to those analyzed by MSI. Drug levels in tissue extracts were measured by liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS). The integrated MSI response was correlated to the LC/MS/MS drug concentrations to determine the amount of drug detected per MSI ion count. The study reported here evaluates olanzapine in liver tissue. Tissue samples containing a range of concentrations were created from liver harvested from rats administered a single dose of olanzapine at 0, 1, 4, 8, 16, 30, or 100 mg/kg. The liver samples were then analyzed by MALDI-MSI and LC/MS/MS. The MALDI-MSI and LC/MS/MS correlation was determined for tissue concentrations of ~300 to 60,000 ng/g and yielded a linear relationship over two orders of magnitude (R(2) = 0.9792). From this correlation, a conversion factor of 6.3 ± 0.23 fg/ion count was used to quantitate MSI responses at the pixel level (100 µm). The details of the method, its importance in pharmaceutical analysis, and the considerations necessary when implementing it are presented.

Sesquiterpenes from termite soldiers. Structure of amiteol, a new 5β, 7β, 10β-eudesmane from amitermes excellens

Abstract The defense secretions of termite soldiers in the genera Amitermes , Noditermes , and Prorhinotermes contain sesqueterpene hydrocarbons, alcohols and ethers. Three new eudesmanes possessing the hitherto unknown 5β, 7β, 10β configuration were identified from Amitermes excellens .

Chemical defense and self-defense: Biochemical transformations of contact insecticides produced by soldier termites

Abstract Soldiers of the advanced genera of rhinotermitids (Isoptera: Rhinotermitidae) produce lipophilic contact insecticides formally derived from fatty acids. Each of these defense substances possesses a reactive electrophilic center (vinyl ketone, nitroalkene, or β-ketoaldehyde) responsible for toxicity. We describe the synthesis of radioactively-labelled defense secretions of two of these species and their use in studying the substrate-selective detoxication by worker termites. Preliminary studies on biosynthesis of defense secretions by termite soldiers are also discussed.

Synthesis and Structure Determination of (3S, 5S)-2,3,5,6-Tetrahydro-3,5-dialkyl-N-(tert-butyloxycarbonyl)-4H-1,4-oxazine-2-ones

Abstract (5S)-2,3,5,6-Tetrahydro-5-alkyl-N-(tert-butyloxycarbonyl)-4H-1,4-oxazine-2-ones, which are readily prepared from optically pure 2-amino alcohols alkylate selectively at the C-3 position to give (3S, 5S)-dialkyl-2,3,5,6-tetrahydro-5-alkyl-N-(tert-butyloxycarbonyl)-4H-1,4-oxazine-2-ones in good yield. The structures of compounds 3e, 5c, 5g, 6h, and 5h (p-bromobenzoate) were determined by single crystal X-ray analysis. The structure of 5b was determined by conversion to optically active diols 6 and 7 and the structure of 5f was determined by correlation to 5c.

New tricyclic diterpene propionate esters from a termite soldier defense secretion

Abstract The structure of 3α, 9β, 13α-trihydroxy-1β, 8β-trinervita-11(12), 15(17)-diene was established by X-ray crystallography. The naturally-occuring tripropionate and dipropionate monoacetate were isolated from the Malaysian termite Nasutitermes sp.

Diastereoselective alkylation of tricarbonyl(methyl 3,5-hexadienoate)iron

Abstract Alkylation of the anion of the title compound with iodomethane, benzylbromide, or allyl bromide proceeds in a highly diastereoselective fashion to afford tricarbonyl(2S*,3R* methyl 2-substituted-3,5-hexadienoate) iron complexes. The relative stereochemistry of the methylation product 2a was determined by single X-ray crystallographic analysis of the corresponding diastereomeric carboxylic acid 4b.

The development of an NMR chemical shift prediction application with the accuracy necessary to grade proton NMR spectra for identity

We have developed an NMR chemical shift prediction system that enables high throughput automatic grading of NMR spectra. In support of high throughput synthetic efforts for our drug discovery program, a rapid and accurate analysis for identity was needed. The system was designed and implemented to take advantage of the NMR assignments that had been tabulated on internally generated research compounds. The system has been operational for four years and has been used in conjunction with an internally written grading program to successfully analyze several hundred thousand samples based only on their 1D 1H spectrum. A focused test of the systems accuracy on 1006 molecules demonstrated the ability to estimate the proton chemical shift with an average error of +/−0.16 ppm. This level of chemical shift accuracy allows for reliable structure confirmation by automated analysis using only proton NMR. Copyright

Synthesis of (2S,5S,4R)-2,5-diamino-3,3-difluoro-1,6-diphenylhydroxyhexane: the core unit of a potent HIV proteinase inhibitor

The coupling of the novel pseudo-symmetrical dipeptide mimic 1a, synthesized via Boc-L-phenylalaninol, with Z-L-valine led to a very potent inhibitor of the HIV proteinase.