Yon-Yih Chen

Diastereofacial selectivity in azomethine ylide cycloaddition reactions derived from chiral α-cyanoaminosilanes

Abstract A series of α-cyanoaminosilanes has been found to act as azomethine ylide equivalents. Treatment of these compounds with silver fluoride in the presence of electron deficient olefins gives substituted pyrrolidines in high yield. The extent ofdiastereoselectivity associated with the 1,3-dipolar cycloaddition of chiral azomethine ylides with several dipolarophiles has been studied. Reasonable levels of such diastereoselectivity have been found when optically active α-cyanoaminosilanes are employed as azomethine ylide equivalents. These compounds can be prepared in multigram quantities by treating the appropriate chiral amine with chlorotrimethylsilane followed by reaction of the resulting secondary amine with formaldehyde in the presence of potassium cyanide. It was found that N-benzyl-N-cyanomethyl-N-trimethylsilylmethylamine undergoes stereospecific cycloaddition with dimethyl fumarate and maleate. The stereospecificity of the reaction is consistent with a concerted cycloaddition reaction.

Synthesis of pyrrolidines using an α-cyanoaminosilane as an azomethine ylide equivalent

Abstract The potential of α-cyanoaminosilane ( 3 ) to act as an azomethine ylide equivalent is illustrated by its treatment with silver fluoride in the presence of electron deficient olefins to give substituted pyrrolidines in high yield.

Modulation of the chemiluminescent signal from N10-(3-sulfopropyl)-N-sulfonylacridinium-9-carboxamides

Acridinium salts 3a-h were synthesized from the corresponding sulfonamides 1a-h and their chemiluminescence profiles were compared. The quantity of light emitted over the time studied did not correlate well with the pKa of sulfonamide leaving group. Rather, steric factors contributed the most to modulating the light output from these compounds. The mesitylsulfonyl substituent of acridinium salt 3d reduced the chemiluminescence signal by 20-fold relative to the reference acridinium salt 3a.

Evaluation of chemiluminescent estradiol conjugates by using a surface plasmon resonance detector.

A series of chemiluminescent 17beta-estradiol probes were synthesized. Relative equilibrium dissociation constants (K(D)) for the interaction of an anti-E(2) Fab fragment for the probes in solution were evaluated using a single E(2)-analog biosensor surface on a BIAcore surface plasmon resonance instrument. The results show the antibody fragment binds all chemiluminescent conjugates tested with high affinity showing only minor preferences for site of substitution (C6 versus C7), stereochemistry (alpha versus beta), or linker moiety.

A stereoselective synthesis of 1α-(3′-Carboxypropyl)-4-androsten-17β-ol-3-one: Preparation of immunoreagents for quantification of testosterone by fluorescence polarization immunoassay

Abstract 1α(3′-Carboxypropyl)-4-androsten-17β-ol-3-one (2), a novel hapten, was prepared from boldenone (3) via addition of 4-pentenyl magnesium bromide in the presence of CuBr, as a key step in >95% epimeric excess and 13.8% overall yield. Two immunogens (7,8) and three fluorescent tracers (11,18,19) were prepared from acid (2) for the development of an immunoassay for testosterone (1).

O-(fluoresceinylmethyl)hydroxylamine (OFMHA): a reagent for the preparation of fluorescent O-(fluoresceinylmethyl)oxime (FMO)-steroid conjugates.

The 5 and 6-isomers of O-(fluoresceinylmethyl)hydroxylamine reacted with a representative sample of oxo-steroids (6-oxoestradiol, estrone, norethindrone, cortisol, progesterone, and digitoxin-dialdehyde) to produce O-(fluoresceinylmethyl)oxime conjugates in a single step in 24-84% yield after preparative high performance liquid chromotography.

Estradiol-mimetic probes. Preparation of 17α-(6-amino-hexynyl)estradiol biotin, fluorescein and acridinium conjugates

3-O-tert-Butyldimethylsilyl-17 alpha-(6-mesyloxyhexynyl)estradiol was converted to the azide in 60-70% yield with NaN3/DMPU, then reduced to the corresponding amine (> 95% yield). Acylation with the N-hydroxysuccinimide esters of biotin, 5-carboxyfluorescein and 10-(3-sulfopropyl)-N-tosyl-N-(3- carboxypropyl)acridinium-9-carboxamide gave the title conjugates. The KDs of the tracers with an estradiol antibody ranged from 97-197 nM.

ω-Aminooxyalkanesulfonic acids. Novel nucleophilic sulfoalkylation reagents

Abstract Electrophilic sulfoalkylation reagents, such as 1,3-propanesultone, are widely used to enhance the hydrophilicity of polymers, proteins, etc. In this report, a series of nucleophilic sulfoalkylation reagents [NH 2 O(CH 2 ) n SO 3 H, n =2, 3, 4] were prepared from the corresponding chloroalkylsulfonyl chlorides.

Development of a dot-blot assay for screening monoclonal antibodies to low-molecular-mass drugs

Dot-blot is a versatile and simple analysis to perform. We adapted this method as a simple identity test for monoclonal antibodies to a number of small compounds: three transplant drugs, an anticonvulsant, a steroid, an anticancer drug, and an antibiotic. Immunology-based identity tests using low-molecular-mass organic compounds have historically been a challenge to develop. We modified the traditional dot-blot assay to serve as an identity test for monoclonal antibodies to carbamazepine, sirolimus, tacrolimus, cyclosporine, cortisol, methotrexate, and gentamicin. The primary obstacle was the immobilization of these organic compounds on nitrocellulose as nitrocellulose is also soluble in most of the organic solvents in which the compounds are soluble. We evaluated different membranes, solvents, and chemical forms of these organic compounds to overcome this challenge. A number of incubation and washing solutions were also investigated. By varying the chemical form, concentration, and incubation conditions, a set of effective and reproducible identity tests were developed for these monoclonal antibodies.