Potentially repurposable drugs for schizophrenia identified from its interactome.

We previously presented the protein-protein interaction network of schizophrenia associated genes, and from it, the drug-protein interactome which showed the drugs that target any of the proteins in the interactome. Here, we studied these drugs further to identify whether any of them may potentially be repurposable for schizophrenia. In schizophrenia, gene expression has been described as a measurable aspect of the disease reflecting the action of risk genes. We studied each of the drugs from the interactome using the BaseSpace Correlation Engine, and shortlisted those that had a negative correlation with differential gene expression of schizophrenia. This analysis resulted in 12 drugs whose differential gene expression (drug versus normal) had an anti-correlation with differential expression for schizophrenia (disorder versus normal). Some of these drugs were already being tested for their clinical activity in schizophrenia and other neuropsychiatric disorders. Several proteins in the protein interactome of the targets of several of these drugs were associated with various neuropsychiatric disorders. The network of genes with opposite drug-induced versus schizophrenia-associated expression profiles were significantly enriched in pathways relevant to schizophrenia etiology and GWAS genes associated with traits or diseases that had a pathophysiological overlap with schizophrenia. Drugs that targeted the same genes as the shortlisted drugs, have also demonstrated clinical activity in schizophrenia and other related disorders. This integrated computational analysis will help translate insights from the schizophrenia drug-protein interactome to clinical research - an important step, especially in the field of psychiatric drug development which faces a high failure rate.

Specificity of the Redox Complex between Cytochrome P450 24A1 and Adrenodoxin Relies on Carbon-25 Hydroxylation of Vitamin-D Substrate.

Metabolic deactivation of 1,25(OH)2D3 is initiated by modification of the vitamin-D side chain, as carried out by the mitochondrial cytochrome P450 24A1 (CYP24A1). In addition to its role in vitamin-D metabolism, CYP24A1 is involved in catabolism of vitamin-D analogs, thereby reducing their efficacy. CYP24A1 function relies on electron transfer from the soluble ferredoxin protein adrenodoxin (Adx). Recent structural evidence suggests that regioselectivity of the CYP24A1 reaction may correlate with distinct modes of Adx recognition. Here we used nuclear magnetic resonance (NMR) spectroscopy to monitor the structure of 15N-labeled full-length Adx from rat while forming the complex with rat CYP24A1 in the ligand-free state or bound to either 1,25(OH)2D3 or the vitamin-D supplement 1α(OH)D3. Although both vitamin-D ligands were found to induce a reduction in overall NMR peak broadening, thereby suggesting ligand-induced disruption of the complex, a crosslinking analysis suggested that ligand does not have a significant effect on the relative association affinities of the redox complexes. However, a key finding is that, whereas the presence of primary CYP24A1 substrate was found to induce NMR peak broadening focused on the putative recognition site α-helix 3 of rat adrenodoxin, the interaction in the presence of 1α(OH)D3, which is lacking the carbon-25 hydroxyl, results in disruption of the NMR peak broadening pattern, thus indicating a ligand-induced nonspecific protein interaction. These findings provide a structural basis for the poor substrate turnover of side-chain-modified vitamin-D analogs, while also confirming that specificity of the CYP24A1-ligand interaction influences specificity of CYP24A1-Adx recognition. SIGNIFICANCE STATEMENT: Mitochondrial cytochrome P450 enzymes, such as CYP24A1 responsible for catabolizing vitamin-D and its analogs, rely on a protein-protein interaction with a ferredoxin in order to receive delivery of the electrons required for catalysis. In this study, we demonstrate that this protein interaction is influenced by the enzyme-ligand interaction that precedes it. Specifically, vitamin-D missing carbon-25 hydroxylation binds the enzyme active site with high affinity but results in a loss of P450-ferredoxin binding specificity.

Concise synthesis of 23-hydroxylated vitamin D3 metabolites.

Three 23-hydroxylated vitamin D3 derivatives, which are metabolites of 25-hydroxyvitamin D3 produced by CYP24A1 and a related diastereomer, were efficiently synthesized. Each C23 hydroxy unit was constructed by the Claisen condensation reaction with ethyl acetate or the Grignard reaction with 2-methylallymagnesium chloride. Stereochemistry at the C23 position was determined by a modified Mosher's method. The triene structures were constructed by the Wittig-Horner reaction utilizing the A-ring phosphine oxide moiety.

Development of a method for multiple vitamin D metabolite measurements by liquid chromatography coupled with tandem mass spectrometry in dried blood spots.

There are two forms of vitamin D which are essential to the human body, i.e. vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). The inactive metabolites of vitamin D are commonly used for quantitative analysis because of their longer half-life, stability, and relatively high blood concentrations. This paper presents the development of a high-throughput and sensitive method for determining four vitamin D metabolites in dried blood spots using liquid chromatography coupled with tandem mass spectrometry. This method allows for the determination of 25(OH)D2 and 25(OH)D3 concentrations, as well as the epimeric form 3-epi-25(OH)D3 and 24,25(OH)2D3. The analyzed material is capillary blood taken from the fingertip, deposited on filter paper. Four different chromatographic columns were tested to separate all compounds, in particular, the epimeric form. The column of choice was F5 (Phenomenex, Torrance, CA, USA). In order to prove the consistency between the results for DBS, used as an alternative biological matrix, and serum, comparative studies of these two materials were carried out in nearly 100 individuals. The results indicated their positive correlation. The evaluation of short-term stability of metabolites in DBS within the month showed no change in metabolite concentration. During the validation, the impact of the matrix on the ionization of the tested compounds was evaluated. Capillary blood and venous blood collected for different anticoagulants were also compared. The smallest differences in the results were obtained for citrate. In order to achieve a limit of quantitation of 0.2 ng ml-1, sample preparation involved derivatization using a Cookson-type reagent, 4-(4'-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione (DAPTAD).

A new suprasterol by photochemical reaction of 1α,25-dihydroxy-9-methylene-19-norvitamin D3.

The UV-induced photochemical reaction of 1α,25-dihydroxy-9-methylene-19-norvitamin D3 has been investigated. The pentacyclic structure of the isolated product has been unequivocally established by X-ray crystallographic analysis. The possible reaction paths of the examined photochemical transformation are discussed. Biological in vivo and in vitro tests proved that the photoproduct is devoid of calcemic activity.

Synthesis and biological activity of 1α,2α,25-trihydroxyvitamin D3: active metabolite of 2α-(3-hydroxypropoxy)-1α,25-dihydroxyvitamin D3 by human CYP3A4.

Our previous studies revealed that recombinant human CYP3A4 converted 2α-(3-hydroxypropoxy)-1α,25-dihydroxyvitamin D3 (O2C3), which was a more potent binder to vitamin D receptor (VDR) than the natural hormone, 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3, 1), to 1α,2α,25-trihydroxyvitamin D3 (2). Here, we synthesized 2 using the Trost Pd-mediated coupling reaction between an A-ring precursor and a CD-ring bromoolefin and evaluated its preliminary biological activity. We found that metabolite 2 from O2C3 was still active as a VDR ligand while maintaining human VDR binding affinity (27.3% of 1α,25(OH)2D3) and HL-60 cell differentiation activity (62% of 1α,25(OH)2D3).

Microbial production of 1α-hydroxyvitamin D3 from vitamin D3.

The microbial transformation of vitamin D3 (1) by the fungi Candida maltosa R42 and Botrytis allii NRRL 2502 was investigated. Incubation of compound 1 with C. maltosa R42 and B. allii NRRL 2502 produced the same three more polar metabolites in small yields. The main metabolite was identified as 1α-hydroxyvitamin D3 (2). This biotransformation has utility as a possible tool for the production of 1α-hydroxyvitamin D3 from the readily available vitamin D3 for patients with compromised kidney function.

Synthesis of 9-alkylated calcitriol and two 1α,25-dihydroxy-9-methylene-10,19-dihydrovitamin D3 analogues with a non-natural triene system by thermal sigmatropic rearrangements.

1α,25-(OH)(2)-9α-Methylvitamin D(3) (4), the first known analogue of the natural hormone 1α,25-(OH)(2)D(3) (3) with an alkyl substituent at C-9, and two 1α,25-(OH)(2)-9-methylene-10,19-dihydrovitamin D(3) analogues (7 and 8) with an unprecedented non-natural triene system were synthesized by thermal isomerization of 1α,25-(OH)(2)-9-methylprevitamin D(3) (6). Three alternative approaches (Sonogashira, Stille, or stereoselective dehydration of a tertiary propargyl alcohol) have been successfully used to construct the dienyne precursors of previtamin 6 possessing two methyl groups capable of participating in the [1,7]-sigmatropic hydrogen shift.

Synthesis and biological activities of 1α,4α,25- and 1α,4ß,25-trihydroxyvitamin D(3) and their metabolism by human CYP24A1 and UDP-glucuronosyltransferase.

A previous report has demonstrated the existence of a C4-hydroxylated vitamin D(2) metabolite in serum of rats treated with pharmacological doses of vitamin D(2). However, the biological significance and metabolic fate of this metabolite have not been described. To explore its potential biological activities, we therefore synthesized 1α,4α,25-trihydroxyvitamin D(3) and its diastereoisomer, 1α,4ß,25-trihydroxyvitamin D(3), using Trost Pd-mediated coupling reaction, and studied their vitamin D receptor (VDR) binding affinity, osteocalcin promoter transactivation activity, and their further metabolism by human CYP24A1 as well as by human liver microsomal fraction based on CYP- and UDP-glucuronosyltransferases (UGTs)-reactions.

Characterizing antibody cross-reactivity for immunoaffinity purification of analytes prior to multiplexed liquid chromatography-tandem mass spectrometry.

BACKGROUND: Immunoassays for 1α,25-dihydroxyvitamin D [1α,25(OH)(2)D] lack analytical specificity. We characterized the cross-reactivity of an anti-1α,25(OH)(2)D antibody with purified vitamin D metabolites and used these data to map the chemical features of 1α,25(OH)(2)D that are important for antibody binding. Additionally, we hypothesized that when combined with isotope-dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS), antibody cross-reactivity could be used to semiselectively enrich for structurally similar metabolites of vitamin D in a multiplexed assay. METHODS: Sample preparation consisted of immunoaffinity enrichment with a solid-phase anti-1α,25(OH)(2)D antibody and derivatization. Analytes were quantified with LC-MS/MS. Supplementation and recovery studies were performed for 11 vitamin D metabolites. We developed a method for simultaneously quantifying 25(OH)D(2), 25(OH)D(3), 24,25(OH)(2)D(3), 1α,25(OH)(2)D(2), and 1α,25(OH)(2)D(3) that included deuterated internal standards for each analyte. RESULTS: The important chemical features of vitamin D metabolites for binding to the antibody were (a) native orientation of the hydroxyl group on carbon C3 in the A ring, (b) the lack of substitution at carbon C4 in the A ring, and (c) the overall polarity of the vitamin D metabolite. The multiplexed method had lower limits of quantification (20% CV) of 0.2 ng/mL, 1.0 ng/mL, 0.06 ng/mL, 3.4 pg/mL, and 2.8 pg/mL for 25(OH)D(2), 25(OH)D(3), 24,25(OH)(2)D(3), 1α,25(OH)(2)D(2), and 1α,25(OH)(2)D(3), respectively. Method comparisons to 3 other LC-MS/MS methods yielded an r(2) value >0.9, an intercept less than the lower limit of quantification, and a slope statistically indistinguishable from 1.0. CONCLUSIONS: LC-MS/MS can be used to characterize antibody cross-reactivity, a conclusion supported by our multiplexed assay for 5 vitamin D metabolites with immunoenrichment in a targeted metabolomic assay.

Synthesis and biological activities of vitamin D-like inhibitors of CYP24 hydroxylase.

Selective inhibitors of CYP24A1 represent an important synthetic target in a search for novel vitamin D compounds of therapeutic value. In the present work, we show the synthesis and biological properties of two novel side chain modified 2-methylene-19-nor-1,25(OH)(2)D(3) analogs, the 22-imidazole-1-yl derivative 2 (VIMI) and the 25-N-cyclopropylamine compound 3 (CPA1), which were efficiently prepared in convergent syntheses utilizing the Lythgoe type Horner-Wittig olefination reaction. When tested in a cell-free assay, both compounds were found to be potent competitive inhibitors of CYP24A1, with the cyclopropylamine analog 3 exhibiting an 80-1 selective inhibition of CYP24A1 over CYP27B1. Addition of 3 to a mouse osteoblast culture sustained the level of 1,25(OH)(2)D(3), further demonstrating its effectiveness in CYP24A1 inhibition. Importantly, the in vitro effects on human promyeloid leukemia (HL-60) cell differentiation by 3 were nearly identical to those of 1,25(OH)(2)D(3) and in vivo the compound showed low calcemic activity. Finally, the results of preliminary theoretical studies provide useful insights to rationalize the ability of analog 3 to selectively inhibit the cytochrome P450 isoform CYP24A1.

Production of 22-hydroxy metabolites of vitamin d3 by cytochrome p450scc (CYP11A1) and analysis of their biological activities on skin cells.

Cytochrome P450scc (CYP11A1) can hydroxylate vitamin D(3), producing 20S-hydroxyvitamin D(3) [20(OH)D(3)] and 20S,23-dihydroxyvitamin D(3) [20,23(OH)(2)D(3)] as the major metabolites. These are biologically active, acting as partial vitamin D receptor (VDR) agonists. Minor products include 17-hydroxyvitamin D(3), 17,20-dihydroxyvitamin D(3), and 17,20,23-trihydroxyvitamin D(3). In the current study, we have further analyzed the reaction products from cytochrome P450scc (P450scc) action on vitamin D(3) and have identified two 22-hydroxy derivatives as products, 22-hydroxyvitamin D(3) [22(OH)D(3)] and 20S,22-dihydroxyvitamin D(3) [20,22(OH)(2)D(3)]. The structures of both of these derivatives were determined by NMR. P450scc could convert purified 22(OH)D(3) to 20,22(OH)(2)D(3). The 20,22(OH)(2)D(3) could also be produced from 20(OH)D(3) and was metabolized to a trihydroxyvitamin D(3) product. We compared the biological activities of these new derivatives with those of 20(OH)D(3), 20,23(OH)(2)D(3), and 1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. 1,25(OH)(2)D(3), 20(OH)D(3), 22(OH)D(3), 20,23(OH)(2)D(3), and 20,22(OH)(2)D(3) significantly inhibited keratinocyte proliferation in a dose-dependent manner. The strongest inducers of involucrin expression (a marker of keratinocyte differentiation) were 20,23(OH)(2)D(3), 20,22(OH)(2)D(3), 20(OH)D(3), and 1,25(OH)(2)D(3), with 22(OH)D(3) having a heterogeneous effect. Little or no stimulation of CYP24 mRNA expression was observed for all the analogs tested except for 1,25(OH)(2)D(3). All the compounds stimulated VDR translocation from the cytoplasm to the nucleus with 22(OH)D(3) and 20,22(OH)(2)D(3) having less effect than 1,25(OH)(2)D(3) and 20(OH)D(3). Thus, we have identified 22(OH)D(3) and 20,22(OH)(2)D(3) as products of CYP11A1 action on vitamin D(3) and shown that, like 20(OH)D(3) and 20,23(OH)(2)D(3), they are active on keratinocytes via the VDR, however, showing a degree of phenotypic heterogeneity in comparison with other P450scc-derived hydroxy metabolites of vitamin D(3).

Hydrogen/deuterium exchange reveals distinct agonist/partial agonist receptor dynamics within vitamin D receptor/retinoid X receptor heterodimer.

Regulation of nuclear receptor (NR) activity is driven by alterations in the conformational dynamics of the receptor upon ligand binding. Previously, we demonstrated that hydrogen/deuterium exchange (HDX) can be applied to determine novel mechanism of action of PPARγ ligands and in predicting tissue specificity of selective estrogen receptor modulators. Here, we applied HDX to probe the conformational dynamics of the ligand binding domain (LBD) of the vitamin D receptor (VDR) upon binding its natural ligand 1α,25-dihydroxyvitamin D3 (1,25D3), and two analogs, alfacalcidol and ED-71. Comparison of HDX profiles from ligands in complex with the LBD with full-length receptor bound to its cognate receptor retinoid X receptor (RXR) revealed unique receptor dynamics that could not be inferred from static crystal structures. These results demonstrate that ligands modulate the dynamics of the heterodimer interface as well as provide insight into the role of AF-2 dynamics in the action of VDR partial agonists.

A new look at the most successful prodrugs for active vitamin D (D hormone): alfacalcidol and doxercalciferol.

Alfacalcidol (1alpha-hydroxyvitamin D(3)) has been widely used since 1981 as a prodrug for calcitriol (1alpha,25-dihydroxyvitamin D(3)) in the treatment of hypocalcemia, chronic renal failure, hypoparathyroidism and osteoporosis. More recently, doxercalciferol (1alpha-hydroxyvitamin D(2)) has been used since 1999 as a prodrug for 1alpha,25-dihydroxyvitamin D(2) for the treatment of secondary hyperparathyroidism. Currently, six forms of vitamin D are known. They range from vitamin D(2) to vitamin D(7 )and are distinguished by their differing side chains. Only vitamin D(2) and vitamin D(3) have been found to be biologically active based on the elucidation of activation pathways. Alfacalcidol and osteoporosis/doxercalciferol and secondary hyperparathyroidism are discussed, with a new look at old compounds including their practical syntheses.

D-hormone derivatives for the treatment of osteoporosis: from alfacalcidol to eldecalcitol.

Many readers may have only a vague idea about vitamin D. This is made complicated, in part, because it is also expressed with suffixes such as vitamin D(2) or vitamin D(3). Otherwise the prefix of "active" is also occasionally used. Vitamin D is often referred to as an important nutrient for calcium intake, especially for growing children and the elderly. On the other hand, it serves as a therapeutic drug for osteoporosis and psoriasis. Recent studies have suggested an association with a number of diseases such as cancer, diabetes and Alzheimer's disease. The author has been involved in the research and development of vitamin D applications for over 25 years, and has often witnessed even world-class experts confuse the two roles - vitamin and hormone - of "substance" D. Assuming some readers are not familiar with vitamin D, D hormone or osteoporosis, an outline of vitamin D and D hormone is delineated with a particular focus on the treatment of osteoporosis. Furthermore, development of alfacalcidol as the first prodrug of D hormone (calcitriol) and eldecalcitol as a characteristic new D hormone derivative and basic relationship between calcemic activity and effect on bone in vitamin D (cholecalciferol), D hormone (calcitriol/alfacalcidol), and a new D hormone derivative (eldecalcitol) are introduced.

Synthesis of gamma- and delta-lactones from 1alpha-hydroxy-5,6-trans-vitamin D3 by ring-closing metathesis route and their reduction with metal hydrides.

New synthetic pathway towards 19-functionalized derivatives of 1alpha-hydroxy-5,6-trans-vitamin D3 was described. Ring-closing metathesis (RCM) of 1alpha-hydroxy-5,6-trans-vitamin D3 1-omega-alkenoates was a key-step. Hydride reduction of resulting lactones led to the new vitamin D3 analogues.

23-carboxy-24,25,26,27-tetranorvitamin D3 (calcioic acid) and 24-carboxy-25,26,27-trinorvitamin D3 (cholacalcioic acid): end products of 25-hydroxyvitamin D3 metabolism in rat kidney through C-24 oxidation pathway.

During the past two and half decades the elucidation of the metabolic pathways of 25OHD(3) and its active metabolite 1alpha,25(OH)(2)D(3) progressed in parallel. In spite of many advances in this area of vitamin D research, the unequivocal identification of the end products of 25OHD(3) metabolism through C-24 oxidation pathway has not been achieved. It is now well established that both 25OHD(3) and 1alpha,25(OH)(2)D(3) are metabolized through the same C-24 oxidation pathway initiated by the enzyme 24-hydroxylase (CYP24A1). Based on the information that the end product of 1alpha,25(OH)(2)D(3) metabolism through C-24 oxidation pathway is 1alpha-OH-23- COOH-24,25,26,27-tetranor D(3) or calcitroic acid; the metabolism of 25OHD(3) into 23-COOH-24,25,26,27-tetranor D(3) has been assumed. Furthermore, a previous study indicated 24-COOH-25,26,27-trinor D(3) as a water soluble metabolite of 24R,25(OH)(2)D(3) produced in rat kidney homogenates. Therefore, 24-COOH-25,26,27-trinor D(3) was also assumed as another end product of 25OHD(3) metabolism through C-24 oxidation pathway. We embarked on our present study to provide unequivocal proof for these assumptions. We first studied the metabolism of 25OHD(3) at low substrate concentration (3x10(-10)M) using [1,2-(3)H]25OHD(3) as the substrate in the perfused rat kidneys isolated from both normal and vitamin D(3) intoxicated rats. A highly polar water soluble metabolite, labeled as metabolite X was isolated from the kidney perfusate. The amount of metabolite X produced in the kidney of a vitamin D intoxicated rat was about seven times higher than that produced in the kidney of a normal rat. We then produced metabolite X in a quantity sufficient for its structure identification by perfusing kidneys isolated from vitamin D intoxicated rats with high substrate concentration of 25OHD(3) (5x10(-6)M). Using the techniques of electron impact and thermospray mass spectrometry, we established that the metabolite X contained both 23-COOH-24,25,26,27-tetranor D(3) and 24-COOH-25,26,27-trinor D(3) in a ratio of 4:1. The same metabolite X containing both acids in the same ratio of 4:1 was also produced when 24R,25(OH)(2)D(3) was used as the starting substrate. Previously, the trivial name of cholacalcioic acid was assigned to 24-COOH-25,26,27-trinorvitamin D(3). Using the same guidelines, we now assign the trivial name of calcioic acid to 23-COOH-24,25,26,27-tetranor D(3). In summary, for the first time our study provides unequivocal evidence to indicate that both calcioic and cholacalcioic acids as the end products of 25OHD(3) metabolism in rat kidney through C-24 oxidation pathway.

An alternative pathway of vitamin D metabolism. Cytochrome P450scc (CYP11A1)-mediated conversion to 20-hydroxyvitamin D2 and 17,20-dihydroxyvitamin D2.

We report an alternative, hydroxylating pathway for the metabolism of vitamin D2 in a cytochrome P450 side chain cleavage (P450scc; CYP11A1) reconstituted system. NMR analyses identified solely 20-hydroxyvitamin D2 and 17,20-dihydroxyvitamin D2 derivatives. 20-Hydroxyvitamin D2 was produced at a rate of 0.34 mol x min(-1) x mol(-1) P450scc, and 17,20-dihydroxyvitamin D2 was produced at a rate of 0.13 mol x min(-1) x mol(-1). In adrenal mitochondria, vitamin D2 was metabolized to six monohydroxy products. Nevertheless, aminoglutethimide (a P450scc inhibitor) inhibited this adrenal metabolite formation. Initial testing of metabolites for biological activity showed that, similar to vitamin D2, 20-hydroxyvitamin D2 and 17,20-dihydroxyvitamin D2 inhibited DNA synthesis in human epidermal HaCaT keratinocytes, although to a greater degree. 17,20-Dihydroxyvitamin D2 stimulated transcriptional activity of the involucrin promoter, again to a significantly greater extent than vitamin D2, while the effect of 20-hydroxyvitamin D2 was statistically insignificant. Thus, P450scc can metabolize vitamin D2 to generate novel products, with intrinsic biological activity (at least in keratinocytes).

An assessment of dose-uniformity of samples delivered from paediatric oral droppers.

BACKGROUND AND OBJECTIVES: To assess the accuracy and precision of delivery from containers containing oral drops, both under optimal laboratory conditions and during use by volunteers using a variety of real pharmaceutical products and specially prepared fluids. METHODS: The effects of the physical properties (viscosity, surface tension, fluid density) of fluids and the angle of a dropper upon the accuracy and precision of dispensing were investigated under standard laboratory conditions. Dose delivery was then assessed using a number of volunteers who were either given no instructions on the use of containers or were instructed to hold the droppers vertically. RESULTS: Viscosity, surface tension, fluid density and residual volume had little or no effect upon the volume of liquid delivered by a dropper clamped in the vertical position. However, when the angle of the dropper was moved towards 45 degrees from the vertical, the volume dispensed declined and became more variable to a point where the requirements of the European Pharmacopoeia were no longer fulfilled. This finding applied to a variety of products. When volunteers used the same droppers manually, the mean volumes dispensed were lower than when the droppers were vertically clamped and the variability was greater. It appeared that these problems were associated with volunteers failing to hold the dropper vertically and the precision and accuracy were indeed increased if the volunteers were instructed as to how the dropper should be held. The results from volunteers were more precise and accurate with the most viscous of the fluids tested and it was speculated that this may have been because the volunteers could more easily use the droppers vertically as there was less fear of dispensing too many drops. CONCLUSIONS: The key factor in achieving satisfactory dispensing from droppers is to ensure that the dropper is held vertically and this should form the basis of instructions to patients. Formulators should consider increasing the viscosity of prepared dropper solutions to reduce further errors in dose.

Conformer-specific photoconversion of 25-hydroxytachysterol to 25-hydroxyprevitamin D3: role in the production of vitamin Ds.

The photochemical goal in the production of vitamin Ds (Vit Ds) is to maximize the conversion of the provitamins (Pros) to the previtamins (Pres) while minimizing stoichiometric losses to undesirable over-irradiation products. The last step in the syntheses, the [1,7]-sigmatropic rearrangement of the Pres to the Vits, is thermally induced. The competition between cis-trans photoisomerization and photocyclization of the Pres is known to be highly excitation-wavelength specific. It inspired Havinga's nonequilibration of excited rotamers (NEER) principle and more recent alternative explanations. In contrast, the photochemistry of tachysterol has been reported to be relatively unexceptional with Tachy --> Pre quantum yields in the 0.10-0.13 range, independent of lambdaexc. Examination of the spectrum of the 25-hydroxy derivative of tachysterol (HOTachy) reveals vibronic structure between 295 and 260 nm and a broad structureless shoulder between 330 and 295 nm. These features are consistent with absorption by at least two Tachy conformers. We show that these conformers differ dramatically in their trans-to-cis photoisomerization efficiency. The Tachy --> Pre quantum yield at 313 nm (0.42) in degassed methanol solution is substantially higher than at 254 nm (0.12). On the basis of recent theoretical predictions, it is likely that 313 nm selectively excites the cEc HOTachy conformer which gives photoisomerization much more efficiently than do the other expected conformers (cEt, most abundant, and tEt). Efficient conversion of HOPro D3 to HOPre D3 is accomplished by a two-stage 254/313-nm irradiation sequence. Use of 313 nm in the second step is preferable to previously proposed much longer wavelengths that were hardly absorbed by HOTachy.