Pritish Chowdhury

Synthesis of some new steroidal [16α,17α-d]-isoxazolines

Abstract Regioselective synthesis of novel steroidal anti-inflammatory ante drug analogues, viz., [16α,17α-d]-isoxazolines 1(a–h) and 2(a–h) prepared in a single step in good yield by the reaction of 16-dehydropregnenolone acetate (16-DPA) 1 or related 21-chloro-20-oxopregnane 2 with various aldoximes (a–h) in presence of chloramine-T in refluxing ethanol.

A convenient synthesis of the side chain of loteprednol etabonate—An ocular soft corticosteroid from 20-oxopregnanes using metal-mediated halogenation as a key reaction

A facile synthesis of the side chain of loteprednol etabonate, namely, chloromethyl-17α-[(ethoxycarbonyl))oxy]-11β-hydro of loteprednol etabonate, viz., chloromethyl-17α-[(ethoxycarbonyl))oxy]-11xy-3-oxoandrosta-1,4-diene-17β-carboxylate--an ocular soft corticosteroid, has been described starting from a 20-oxopregnane, namely, 3β-acetoxy-pregn-5(6),16(17)-diene-20-one (16-dehydropregnenolone acetate, i.e., 16-DPA) using our recently developed metal-mediated halogenation as a key reaction.

Ceric ammonium nitrate (CAN)-a useful catalyst for the rapid and high-yield esterification of carboxylic acids and alcohols with special reference to steroid and other multi-functional natural products

Ceric ammonium nitrate (CAN) acts as a versatile catalyst for the esterification of carboxylic acids and alcohols, including steroids and other multi-functional natural products, in excellent yields under mild and convenient reaction conditions.

Microwave (MW) irradiated Ugi four-component reaction (Ugi-4CR): Expedited synthesis of steroid–amino acid conjugates – A novel class of hybrid compounds

Microwave (MW) assisted chemical reactions are currently gaining considerable importance in organic synthesis to contribute in green technology. Considering the importance of peptidomimetic steroid-amino acid conjugates - a novel class of hybrid compounds having diverse biological properties, we report here synthesis of these compounds of alanine and valine methyl esters with seco-steroids (A, B and D ring cleavage) in expedited way by MW promoted Ugi-four-component reaction (Ugi-4CR).

Microwave (MW) promoted high yield expedient synthesis of steryl ferulates--A class of novel biologically active compounds: A comparative study of their antioxidant activity with that of naturally occurring γ-oryzanol.

Synthetic steryl ferulates [3-O-(trans-4-feruloyl)-sterols] are currently gaining considerable importance in recent years to be used as nutraceuticals and food additives as well as in pharmaceutical applications substituting γ-oryzanol - a class of naturally occurring steryl ferulates having potent antioxidant and other organoleptic properties. Considering the importance of this class of compounds coupled with green technology associated with microwave energy (MW) in organic synthesis, we report here an expedited and high yield synthesis of steryl ferulates from abundant steroids, viz., cholesterol, cholestanol, stigmasterol, stigmastanol, β-sitosterol, β-campesterol, β-campestanol and ergosterol applying MW energy in the crucial step of esterification process of sterols with trans-4-O-acetylferulic acid to furnish their esterified products, viz., 3-O-(trans-4-O-acetylferuloyl)-sterols for their eventual deprotection to their respective steryl ferulates. We further report an efficient and scalable process of producing acetylferulic acid. Testing of synthesized steryl ferulates against antioxidant assays has also been highlighted.

An Efficient Method for the Extraction of Polyphenolics from Some Traditional Varieties of Rice of North-East India

Polyphenolics are secondary metabolites having numerous health benefits. One of the potential sources of phenolics is rice. Despite being the staple food of India, phenolic extraction from rice has not gained much significance due to its concentration in the aleurone layer which is lost during processing. Two procedures were studied for the effective extraction of total phenolics from rice: ultrasound-assisted aqueous methanol extraction and aqueous methanol extraction. The results indicated that ultrasound aided extraction improved the levels of phenolic content by 1.3–2.8 times.

Functionalisation at the C-16 position of 16-dehydro-20-oxopregnanes (steroid drug intermediates) via vinyl nitration with CAN-NaNO2-CH3CN system

16-Dehydro-20-oxopregnanes react with the CAN-NaNO2-CH3CN system to furnish vinyl nitro derivatives, viz, 16-dehydro-16-nitro-20-oxopregnanes while Δ5-steroids react with the system to furnish Δ4-6α and Δ4-6β nitro steroids with complete suppression of the acetamidation reaction on the double bond in both cases.