Girish K. Trivedi

Synthesis of 2, 2-Dimethyl-2H-chromenes via a Palladium (II) Catalysed Reaction

Abstract The antijuvenile hormones Precocene-I, Precocene-II and other bioactive 2, 2-dimethyl-2H-chromenes have been synthesised by intramolecular oxidative cyclisation of 2-isoprenyl phenols catalysed by a palla-dium(II) salt.

Regioselective synthesis of substituted pterocarpans and pterocarpenes. Lewis acid Ti (IV) promoted formal (3+2) cycloaddition reactions.

Abstract A synthesis of novel pterocarpans ( 8a–e , 10a–c and 11a–e ) and pterocarpenes ( 7a–d and 9a–c ) has been carried out. This method involves the Lewis acid Ti (IV) promoted formal (3+2) cycloaddition reaction of 2-alkoxy-1,4-benzoquinones ( 6a–c ) with appropriately substituted 2 H -chromenes ( 1a–b , 2a–b and 5 ) at −78°C.

Synthesis, Chemical Transformation and Antimicrobial Activity of a Novel Class of Nitroolefins: 1,3-Diaryl-2-nitroprop-1-enes

Abstract The synthesis of novel, biologically active 1,3-diaryl-2-nitroprop-1-enes (4) is reported. The synthesis involves condensation between aromatic aldehydes (1) and β-aryl nitroethanes (3). The chemical transformation of the nitro group in diaryl nitropropenes to a carbonyl function has resulted in a new route to the synthesis of an α-hydroxy analog (7c) of a naturally occurring 3, 3′, 4, 4′-tetramethoxy chalcone. The antimicrobial activity of the 1, 3-diaryl-2-nitroprop-1-enes (4a-j) was tested against three gram positive bacteria, two gram negative bacteria and two fungi. These compounds exhibited broad spectrum antimicrobial activity.

An efficient and stereoselective synthesis of (2R,2′S)-1-O-(2′-hydroxyhexadecyl)glycerol and its oxo analogs: Potential antitumour compounds from Shark Liver Oil

Abstract Reproducible, high-yielding, cost efficient, regio- and stereoselective synthesis of the title compound 3 isolated from Shark Liver Oil has been described. The compound 3 is prepared in an overall yield of 41% from chiral synthon 4 by the sequential reaction of 4 with C-13 Wittig salt; hydrogenation; epoxidation and regioselective opening. The oxo analogs 18 and 19 are prepared from four different achiral synthons by the sequential regioselective opening of the corresponding epoxide with different alcohols, methylation and deprotection strategies.

Phase-transfer-catalyzed d-glucosylation: Synthesis of benzoylated aryl β-d-glucopyranosides and β-d-glucopyranosyl-substituted cinnamates

Abstract Phase-transfer-catalyzed d -glucosylation of chelated phenolic aglucons and substituted cinnamic acids, using 2,3,4,6-tetra- O -benzoyl-α-glucopyranosyl bromide, resulted in the stereospecific formation of benzoylated aryl β-glucopyranosides and substituted-β- d -glucopyranosyl cinnamates, respectively, in good pyranosides and substituted-β- d -glucopyranosyl cinnamates, respectively, in good yields. The results conclusively disproved an earlier report that the phase-transfer method requires a nonparticipating group at C-2 or C-6 in the carbohydrate moiety. 1,2,3,4,6-Penta- O -benzoyl-β- d -glucopyranose was obtained as a minor side-product in all of these reactions. The possible mechanism of the phase-transfer method is discussed.

Syntheses of potential spin probes for biomembranes : tempo and proxyl nitroxides of lithocholic acid

Abstract The synthesis of a steroidal spin label 10 containing a tempo nitroxide group in the side chain of lithocholic acid 1 is reported. This is the first report of a tempo nitroxide in a steroidal side chain. The methodology involved a Wittig condensation between the steroidal phosphonium ylide 7 and tempone 9 . The synthesis of a proxyl nitroxide 16 with the proxyl group in the side chain of 1 is also described. A mild oxidation of 16 to the corresponding 3-keto spin label 17 in high yield is also achieved.

1-[2-Hydroxy-3-octadecan-1'-oate]propyl-2″, 2″, 5″, 5″-tetramethyl pyrolidine-N-oxyl-3″-carboxylate as a potential spin probe for membrane structure studies

The synthesis of a new minimum steric perturbing proxyl nitroxide, which is a derivative of glycerol and contains a stearic acid moiety, has been carried out. Its localization in model membrane L-alpha-dipalmitoyl phosphatidyl choline (DPPC) was ascertained with the help of ESR, DSC, 1H and 31P NMR techniques. The nitroxide was used for detecting the changes in the phase transition temperature of the model membranes in the presence and absence of drugs. The permeation of the vasodilating drug epinephrine has also been studied using this spin label. The results prove the potential applicability of the new spin probe in the spin labeling of biomembranes.

Synthesis of 2'-(3α-benzyloxy-24-norcholan-23-yl)-2',4',4'-trimethyl- 4',5'-dihydrooxazoline-n-oxyl - a new potential spin probe for biomembranes

Abstract The synthesis of a new steroidal nitroxide, viz. 2-(3α-benzyloxy-24-norcholan-23-yl)-2,44-trimethyl-4,5- dihydrooxazoline-n-oxyl 7 , a potential spin probe for bio- membranes is described. The title compound in improved yield could be obtained by a direct Grignard reaction on the oxaziridine 4 . This effected a one-step reduction in the overall synthetic sequence. The methodology of the Grignard reaction on the oxaziridine to yield the nitroxide is reported for the first time. In dilute solutions, the isotropic ESR parameters for 7 have been measured.

SYNTHESIS OF POTENTIAL PREGNENOLONE AND PROGESTERONE SPIN PROBES FOR BIOMEMBRANES AND IMMUNOASSAYS

Abstract The synthesis and characterization of four new steroidal spin labels, viz., 3′-[[(pregn-5-en-3β-ol-20S-yl)methyl]oate]-2′,2′,5′,5′-tetramethylpyrrolidine-1′-oxyl,3′-[[(pregn-4-en-3-one-20S-yl)methyl]oate]-2′, 2′,5′,5′-tetra methyl pyrrolidine-1′-oxyl, 3″-[(3β-acetoxypregn-5-en-20-one-16α-yl)prop-2′ξ-ol-3′ξ-oate]-2″,2″,5″,5″-tetramethyl pyrrolidine-1″-oxyl and 3″-[(pregn-5-en-3.20-dione-16α-yl)prop-2′ξ-ol-3′ξ-oate]-2′,2′,5′,5′-tetramethylpyrrolidine-1′-oxyl has been described which involves functionalization of the parent hormone at C-20 and C-16. The key step to all the products was the condensation of 3-carboxyproxyl with the derivatized synthons.

Studies on cycloaddition reactions of 2,2-dimethyl-3,4-dihydro-2H-pyrrole N-oxide and N-(benzylidene)methylamine N-oxide with α,β-unsaturated lactones & esters

Abstract Intermolecular asymmetric 1,3-dipolar cycloaddition of 2,2-dimethyl-3,4-dihydro-2H- pyrrole N-oxide and N-(benzylidene)methylamine N-oxide with optically active α,β-unsaturated esters 1,2,4 and 7–9 provided the corresponding diastereomers while chiral sugar lactones gave stereoselectively the cycloadducts 17a and 17b (in the case of dipolarophile 3) and 18 in (the case of the dipolarophile 6) with the acyclic nitrone B. The stereochemistry of the products has been established using high field nmr techniques. The regioselectivities of these reactions are inconsistent with FMO coefficients and are explained on the basis of charge distribution obtained through AM1 calculations.