Synthesis of a new enantiomerically pure P-chiral phosphine and its use in probing the mechanism of the Mitsunobu reaction

A new enantiomerically pure P-chiral phosphine, (S)-cyclohexylmethyl- (1-naphthyl)phosphine (1) was prepared by phosphine-borane methodology and used in a mechanistic study of the Mitsunobu reaction. Enantiomerically enriched (S)-cyclo- hexylmethyl(1-naphtyl)phosphine oxide (8) is obtained if the reaction proceeds through the phosphonium salt 4, whereas the intermediate dialkoxyphosphorane 5 leads to racemic phosphine oxide 8. The results of the experiments including the variation of the reaction conditions and the natures of alcohol and carboxylic acid used in the Mitsunobu reaction prove the competition of two alternative mechanisms (reaction via 4 or 5) on the second stage of the Mitsunobu reaction.     

New highly calcemic 1 alpha,25-dihydroxy-19-norvitamin D(3) compounds with modified side chain: 26,27-dihomo- and 26,27-dimethylene analogs in 20S-series

New highly potent 2-substituted (20S)-1 alpha,25-dihydroxy-19-norvitamin D(3) analogs with elongated side chain were prepared by Wittig-Horner coupling of A-ring phosphine oxide with the corresponding protected (20S)-25-hydroxy Grundmann's ketones. Biologic evaluation in vitro and in vivo of the synthesized compounds was accomplished. All the synthesized vitamins possessing a 25-hydroxylated saturated side chain were slightly less active (3-5X) than 1 alpha,25-dihydroxyvitamin D(3) in binding to the porcine intestinal vitamin D receptor and significantly more potent (12-150X) in causing differentiation of HL-60 cells. In vivo, 2-methylene-26,27-dihomo and 2 alpha-methyl-26,27-dimethylene analogs were at least 10 times more active, and 2 alpha-methyl-26,27-dihomo compound at least 5 times more active than the vitamin D hormone both in stimulating intestinal calcium transport and bone calcium mobilization (serum calcium increase). It was also established that a 260 pmol dose of the corresponding 2 beta-methyl analogs had a similar effect on intestinal calcium transport and a much more pronounced effect on bone calcium mobilization as the same dose of 1 alpha,25-dihydroxyvitamin D(3).     

New derivative of 1alpha,25-dihydroxy-19-norvitamin D3 with 3'-alkoxypropylidene moiety at C-2: synthesis, biological activity and conformational analysis

In pursuit of novel biologically active Vitamin D compounds of potential therapeutic value, 1alpha,25-dihydroxy-2-[3'-(methoxymethoxy)propylidene]-19-norvitamin D(3) (7) was efficiently prepared in a convergent synthesis, starting with (-)-quinic acid and the protected 25-hydroxy Grundmann ketone 16. The key synthetic step involved Lythgoe type Wittig-Horner coupling of 16, with the phosphine oxide 15. Molecular modeling was employed to establish the A-ring conformation of the synthesized Vitamin 7. Also, preliminary modeling of its complex with the rVDR was performed and interactions between ligand and the binding domain analyzed. Analog 7 was found to be only six times less potent than 1alpha,25-(OH)(2)D(3) (1) in binding to the rat recombinant Vitamin D receptor (VDR). In comparison with hormone 1, it also showed slightly lower cellular HL-60-differentiation activity. Preliminary in vivo tests indicated unusually high calcemic activity of 7.     

The preparation of 2,6-disubstituted pyridinyl phosphine oxides as novel anti-cancer agents

A series of 2,6-dimethoxylpyridinyl phosphine oxides have been synthesized and examined for their antitumor activity. 2,6-Dimethoxy-3-phenyl-4-diphenylphosphinoylpyridine 2 has been employed as the lead compound for this study. We found out that the presence of phosphine oxide on the 2,6-dimethoxylpyridine ring is important for the antitumor activity; the presence of bromine on this core leads to a further enhancement of its antitumor activity. This is the first reported work on the antitumor activity of the 2,6-dimethoxy-3,5-dibromopyridinyl phosphine oxide 5b towards MDAMB-231 breast cancer and SKHep-1 hepatoma cell lines.     

The resolution of acyclic P‐stereogenic phosphine oxides via the formation of diastereomeric complexes: A case study on ethyl‐(2‐methylphenyl)‐phenylphosphine oxide

As an example of acyclic P‐chiral phosphine oxides, the resolution of ethyl‐(2‐methylphenyl)‐phenylphosphine oxide was elaborated with TADDOL derivatives, or with calcium salts of the tartaric acid derivatives. Besides the study on the resolving agents, several purification methods were developed in order to prepare enantiopure ethyl‐(2‐methylphenyl)‐phenylphosphine oxide. It was found that the title phosphine oxide is a racemic crystal‐forming compound, and the recrystallization of the enantiomeric mixtures could be used for the preparation of pure enantiomers. According to our best method, the (R)‐ethyl‐(2‐methylphenyl)‐phenylphosphine oxide could be obtained with an enantiomeric excess of 99% and in a yield of 47%. Complete racemization of the enantiomerically enriched phosphine oxide could be accomplished via the formation of a chlorophosphonium salt. Characterization of the crystal structures of the enantiopure phosphine oxide was complemented with that of the diastereomeric intermediate. X‐ray analysis revealed the main nonbonding interactions responsible for enantiomeric recognition.     

Convenient preparation of A-ring fused pyridines from steroidal enamides

A facile strategy for the preparation of A-ring fused pyridosteroids has been accomplished in high yields by the reaction of Vilsmeier reagent (chloromethyleneiminium salt) with steroidal A-ring enamides (2- and 3-ene) under thermal conditions. The structure of 6'-chloro-5alpha-cholest [3,2-b]pyridine was determined by X-ray analysis.     

Thiono compounds. 4. In vitro mutagenic and antineoplastic activity of TEPA and thio-TEPA

Tris (1-aziridinyl) phosphine oxide (TEPA) and tris (1-aziridinyl) phosphine sulfide (thio-TEPA) induced base pair mutations in the Ames mutagenic assay. Thio-TEPA required metabolic activation while TEPA was active without metabolic activation. Growth of a human vaginal carcinoma (A431), a human breast carcinoma (MDAMB-231), and a human cervical carcinoma (HeLa) were inhibited in soft agar in vitro at concentrations which induced mutagenesis in the Ames Assay. A fourth line, JEG choriocarcinoma, was sensitive to the antigrowth properties of both drugs at concentrations below that which induced mutagenesis. These data suggest that as more antineoplastic agents become available, and as mean survival times increase, knowledge of the relative in vitro sensitivity of a patient's neoplasm to a specific antineoplastic drug (i.e., dose required for growth inhibition) as a function of its mutagenic index might be useful for prediction of clinical remission, as well as the risk of secondary neoplasm induction.Abbreviations TEPA tris (1-aziridinyl) phosphine oxide - thio-TEPA tris (1-aziridinyl) phosphine sulfide - MEM Minimal Essential Media This study was supported by PHS grant No. CA 30321 awarded by the National Cancer Institute (DHHS).     

Steroid degradation in Comamonas testosteroni

Steroid degradation by Comamonas testosteroni and Nocardia restrictus have been intensively studied for the purpose of obtaining materials for steroid drug synthesis. C. testosteroni degrades side chains and converts single/double bonds of certain steroid compounds to produce androsta-1,4-diene 3,17-dione or the derivative. Following 9α-hydroxylation leads to aromatization of the A-ring accompanied by cleavage of the B-ring, and aromatized A-ring is hydroxylated at C-4 position, cleaved at Δ4 by meta-cleavage, and divided into 2-hydroxyhexa-2,4-dienoic acid (A-ring) and 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid (B,C,D-ring) by hydrolysis. Reactions and the genes involved in the cleavage and the following degradation of the A-ring are similar to those for bacterial biphenyl degradation, and 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid degradation is suggested to be mainly β-oxidation. Genes involved in A-ring aromatization and degradation form a gene cluster, and the genes involved in β-oxidation of 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid also comprise a large cluster of more than 10 genes. The DNA region between these two main steroid degradation gene clusters contain 3α-hydroxysteroid dehydrogenase gene, Δ5,3-ketosteroid isomerase gene, genes for inversion of an α-oriented-hydroxyl group to a β-oriented-hydroxyl group at C-12 position of cholic acid, and genes possibly involved in the degradation of a side chain at C-17 position of cholic acid, indicating this DNA region of more than 100kb to be a steroid degradation gene hot spot of C. testosteroni. Article from a special issue on steroids and microorganisms.     

Semisynthesis and antiproliferative evaluation of a series of 3′-aminoflavones

A series of 3′-aminoflavones 5,6,7,8-tetra- or 5,7-dioxygenated on the A-ring was synthesized from tangeretin or naringin, two natural Citrus flavonoids. These flavones were evaluated for antiproliferative activity, activation of apoptosis, and inhibition of tubulin assembly. The most antiproliferative flavones exhibit a common 5-hydroxy-6,7,8-trimethoxy substitution pattern on the A-ring.     

Ab initio electronic structure of the progestogen norethisterone and its 5 alpha-derivatives

The steroid 17 alpha-ethynyl-19-nor-4-androsten-17 beta-ol, 3-one (Norethisterone; NET) and its 5 alpha-dihydro (5 alpha-NET), 3 alpha- and 3 beta-tetrahydro derivatives (3 alpha,5 alpha- and 3 beta,5 alpha-NET), were comparatively studied by the ab initio quantum mechanics theory. Additionally, 5 alpha-androstan-3 beta,17 beta-diol (ADIOL) was also studied. The Hartree-Fock method and the 6-31G(*) basis set were used to obtain the lowest energy conformation, geometries, electronic structure and physicochemical properties of the steroids. The results showed bond distances and valence angles similar among all steroids, but some differences in dihedral angles in the A-B-ring system were observed. The electronic structure analysis showed that NET has both frontier orbitals that is, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) located at the C4-C5 pi-bond. In A-ring reduced derivatives, the HOMO was found at the 17 beta-OH and ethynyl groups. In the case of 5 alpha-NET, the LUMO was confined to the A-ring and its C3 carbonyl group while the two NET tetrahydro-reduced derivatives showed the LUMO at the 17 beta-OH and ethynyl groups. The energy changes of the rotational barrier of the 17 beta-OH group suggest that its movement is somewhat restricted by the 17 alpha-ethynyl group. Interestingly both groups at C17 form a single electrostatic potential with high electronic density. On the other side, the 19-nor condition increases the A-ring mobility. However, the 3 beta-OH group of 3 beta,5 alpha-NET may rotate without significant energy differences as compared to the same group in ADIOL. The electronic structure of NET and its A-ring reduced derivatives explains in some extent their interaction with androgen and progesterone receptors as well as their selectivity for the estrogen alpha-receptor.     

An analog of 1alpha,25-dihydroxy-19-norvitamin D3 with the 1alpha-hydroxy group fixed in the axial position lacks biological activity in vitro

The relationship between the A-ring chair conformation of vitamin D compounds and their ability to bind the vitamin D receptor (VDR) has long attracted the attention of many researchers. It was established that in the crystalline complexes of hVDRmt with the natural hormone, 1alpha,25-dihydroxyvitamin D(3) (1), and its side-chain analogs the vitamins exist in beta-chair form with an equatorial orientation of 1alpha-OH. However, with all these ligands the interconversion between both A-ring forms would be possible in solution. In an attempt to verify the conformation of vitamin D compounds required for binding the VDR we prepared analog 4, characterized by the presence of an axial 1alpha-hydroxy group. Since the additional ring connecting 3beta-oxygen and C-2 prevents A-ring conformational flexibility, the synthesized vitamin 4 can exist exclusively in the alpha-chair form. The geometrical isomer 5 with a free 3beta-OH group was also obtained. The analog 5 binds very poorly to VDR, whereas the vitamin 4 is practically devoid of binding ability. Both compounds also show very low HL-60-differentiating activity. When tested in vivo in mice the analogs 4 and 5 exhibit significant calcemic responses with analog 4 showing more activity than analog 5.     

Synthesis and photophysical studies of tetrazolate‐based Eu(III) photoluminescent ternary complexes containing N‐heterocyclic phosphine oxides auxiliary co‐ligands

Two new ternary tetrazolate Eu(III) complexes with phosphine oxide co‐ligands Eu(PTO)₃·(P1/P2) [PTO = 5‐(2‐pyridyl‐1‐oxide)tetrazole, P1 = diphenylphosphorylamino‐phenylphosphoryl‐benzene, P2 = diphenylphosphorylpyridine)‐bis‐isobutyricphosphoryl] were synthesized and characterized using UV, fluorescence, IR and ¹H NMR spectroscopic techniques. The analytical data prove that the complexes are mononuclear in nature and the central Eu(III) ion is coordinated by three N and three O atoms of tetrazolate, and two O atoms of the corresponding bidentate phosphine oxide ligands. The ancillary ligand increased the photoluminescence efficiency of Eu(PTO)₃·P1 (complex 3) by twofold compared with our previously reported Eu(PTO)₃ complex (complex 1). Copyright © 2015 John Wiley & Sons, Ltd.     

2,2-Functionalized analogues of 1alpha,25-dihydroxyvitamin D3, the potent inducers of cell differentiation

All four possible A-ring stereoisomers of 2,2-dimethyl-1,25-dihydroxyvitamin D(3) (4) were designed and convergently synthesized. Nine-step conversion of methyl hydroxypivalate 6 provided the desired A-ring enyne synthon (13a,b) in good overall yield. Cross-coupling reaction of the A-ring synthon 13a,b with the CD-ring portion in the presence of palladium catalyst, followed by deprotection, gave the vitamin analogues (4a-d). We also synthesized four stereoisomers of 2,2-ethano-1,25-dihydroxyvitamin D(3) (5), as novel spiro-ring analogues having cyclopropane fused at the C2 position. Biological potencies of the synthesized compounds were assessed in terms of the vitamin D receptor (VDR) binding affinity, as well as the HL-60 cell differentiation-inducing activity. The 2,2-ethano analogue 5a showed a comparable activity to the natural hormone 1, while the 2,2-dimethyl analogue 4a exhibited one-third of the activity of 1 in cell differentiation, with the reduced VDR binding affinity.     

Efficient synthesis and biological evaluation of all A-ring diastereomers of 1alpha,25-dihydroxyvitamin D3 and its 20-epimer

An improved synthesis of the diastereomers of 1alpha,25-dihydroxyvitamin D3 (1) was accomplished utilizing our practical route to the A-ring synthon. We applied this procedure to synthesize for the first time all possible A-ring diastereomers of 20-epi-1alpha,25-dihydroxyvitamin D3 (2). Ten-step conversion of 1-(4-methoxyphenoxy)but-3-ene (6), including enantiomeric introduction of the C-3 hydroxyl group to the olefin by the Sharpless asymmetric dihydroxylation, provided all four possible stereoisomers of A-ring enynes (3). i.e., (3R,5R)-, (3R,5S)-, (3S,5R)- and (3S,5S)-bis[(tert-butyldimethylsilyl)oxy]oct-1-en-7-yne, in good overall yield. Palladium-catalyzed cross-coupling of the A-ring synthon with the 20-epi CD-ring portion (5), (E)-(20S)-de-A,B-8-(bromomethylene)cholestan-25-ol, followed by deprotection, afforded the requisite diastereomers of 20-epi-1alpha,25-dihydroxyvitamin D3 (2). The biological profiles of the synthesized stereoisomers were assessed in terms of affinities for vitamin D receptor (VDR) and vitamin D binding protein (DBP). HL-60 cell differentiation-inducing activity and in vivo calcium-regulating potency in comparison with the natural hormone.     

The effects of A-ring and D-ring metabolites of estradiol on the proliferation of vascular endothelial cells

The effects of 14 estradiol metabolites on the proliferation of cultured endothelial cells of human umbilical cord veins were examined and compared with that of their parent substance estradiol. The relationship between dosage and effect was tested over the pharmacological concentration range of 10(-8) to 10(-5) M. Estradiol showed a biphasic behaviour, in the form of stimulation at low concentrations and inhibition at the highest concentration. All 10 A-ring metabolites tested stimulated the growth of the endothelial cells at the lower concentrations. At the highest concentration, the 5 A-ring metabolites: 2-hydroxyestrone, 2-hydroxyestradiol, 2-hydroxyestriol, 4-hydroxyestrone and 4-hydroxyestradiol caused significant inhibitions. Except for the 2-hydroxyestradiol, methylation of these metabolites resulted in the loss of the proliferation inhibiting effect. The D-ring metabolites showed no marked effects compared to the A-ring metabolites except for 16alpha-hydroxyestrone which had an inhibiting effect from 10(-7) to 10(-5) M. Our results show that estradiol metabolites can influence the growth of vascular endothelial cells in the concentration range tested. While the antiproliferative action of 2-methoxyestradiol has been known for some time this study is the first to show the potential capacity of non-methylated metabolites of the A-ring metabolism in inhibiting endothelial proliferation. This may open up new clinical pharmacological aspects in the anti-angiogenetic treatment of tumors.     

Highly potent cell differentiation-inducing analogues of 1alpha,25-dihydroxyvitamin D3: synthesis and biological activity of 2-methyl-1,25-dihydroxyvitamin D3 with side-chain modifications

Eight 2-methyl substituted analogues of 20-epi-22R-methyl-1alpha,25-dihydroxyvitamin D3 (5) and 20-epi-24,26,27-trihomo-22-oxa-1alpha,25-dihydroxyvitamin D3 (6: KH-1060) were convergently synthesized. Preparation of the CD-ring portions with modified side chains of 5 and 6, followed by palladium-catalyzed cross-coupling with the A-ring enyne synthons (20a-d), (3S,4S,5R)-, (3S,4R,5R)-, (3S,4S,5S)- and (3R,4R,5S)-3,5-bis[(tert-butyldimethylsilyl)oxy]-4-methyloct-1-en-7-yne, afforded two sets of four A-ring stereoisomers of 20-epi-2,22-dimethyl-1,25-dihydroxyvitamin D3 (7a-d) and 20-epi-24,26,27-trihomo-2-methyl-22-oxa-1,25-dihydroxyvitamin D3 (8a-d). The biological profiles of the hybrid analogues were assessed in terms of affinity for vitamin D receptor (VDR) and HL-60 cell differentiation-inducing activity in comparison with the natural hormone. The combined modifications of the A-ring at the 2-position and the side chain yielded analogues with high potency.