G. S. R. Subba Rao

Birch reduction and its application in the total synthesis of natural products

The unique availability of substituted cyclohexa-1,4- and 1,3-dienes, notably enol ethers, from Birch reduction of anisoles, permits many novel synthetic reactions of general utility. The total synthesis of several natural products derived from polyketides have been accomplished using a Diels–Alder and Alder–Rickert process. The strategies of the synthesis are discussed.

Crystalline constituents of euphorbiaceae—V: New lignans from Phyllanthus niruri Linn—The constitution of phyllanthin☆

Abstract An improved method for the isolation of phyllanthin and hypophyllanthin from the leaves of Phyllanthus niruri Linn. has been described. Their molecular formulae have been revised as C 24 H 34 O 6 and C 24 H 30 O 7 . The structure of phyllanthin is now shown to be (+)3,4,3′,4′,9,9′-hexamethoxy-8:8′-butyrolignan (IV) from its reactions and degradation to veratric acid. NMR spectra of phyllanthin and its derivatives support this structure.

Chemistry of terminalia species—VI : The constitution of tomentosic acid, a new triterpene carboxylic acid from terminalia tomentosa wight et arn

Abstract From the heartwood of T. tomentosa Wight et Arn, β-sitosterol, oleanolic acid (VI, R = R1 = H), arjunolic acid (I) and barringtogenol (IV) were isolated and in addition a new tetrahydroxy triterpene mono-carboxylic acid, now named Tomentosic acid. The triacetylmethyl tomentosate was oxidized to the corresponding ketone (XV) which could be reduced by forced Wolff-Kishner method to give methyl arjunolate (III). The above ketone also suffered isomerization in presence of alkali to give an α,β-unsaturated ketone (XVI). Further, during lactonization, the acid gives a trihydroxy anhydrolactone (X). The triacetylmethyl ester may be dehydrated using selenium dioxide to give methyldehydro arjunolate (XIX). From these reactions tomentosic acid is tentatively expressed as 2α,3β,19β,23-tetrahydroxy-olean-12-ene-28-oic acid (XII, R = H).

Chemistry of Terminalia species—III Chemical examination of Terminalia paniculata roth : Isolation of 3,3t́-di-o-methyl ellagic acid-4-glucoside

A new glucoside of di-methyl ellagic acid has been isolated from the heartwood of Terminalia paniculata together with β-sitosterol and a new triterpene carboxylic acid. The glucoside is the 4-mono glucoside of 3,3′-di-O-methyl ellagic acid.

Crystalline constituents of euphorbiaceae-VI: The synthesis and absolute configuration of phyllanthin

Abstract (+)Phyllanthin is now shown to be (8S, 8′S) 3,4,3′,4′,9,9′-hexamethoxy-8-8′-butyrolignan (III) by its synthesis from (a) (−)eudesmin (I) and (b) (+)2,3-diveratryl succinic acid (IV). (+)3,4-diveratryl tetrahydrofuran (VI) from (+)phyllanthin is now shown to posses 3S,4S configuration by its formation from (+)2,3-diveratryl-1,4-butane diol (II).

Heteroatom assisted Beckmann fragmentation: towards the synthesis of (±) modhephene

An efficient radical cyclisation-Beckmann fragmentation and a Beckmann fragmentation–radical cyclisation strategy for the synthesis of a [4.3.3]propellane derivative is described.

Vinyl radical induced Michael additions: total synthesis of (−)-seychellene

A new strategy for the total synthesis of (±)-seychellene which involves (i) a regiospecific construction of a bicyclo(2.2.2)octene moiety having a methyl group at the bridgehead and (ii) a vinyl radical induced intramolecular Michael addition is described.

Volatile constituents of Clausena willdenovii: Structures of the furanoterpenes α-clausenan, diclausenan A and diclausenan B

Four furanoid terpenic compounds, α-clausenan, rosefuran (γ-clausenan) and diclausenans A and B, were isolated from the essential oil of the leaves of Clausena willdenovii. Their structures were determined by chemical and spectral data. The occurrence of a high concentration of rosefuran is noteworthy. Selenium dioxide oxidation of diclausenan gave an unusual product, identified as an epoxy-dicarbonyl compound.

Synthetic Triterpenoid Cyano Enone of Methyl Boswellate Activates Intrinsic, Extrinsic, and Endoplasmic Reticulum Stress Cell Death Pathways in Tumor Cell Lines

We explored the effect of a novel synthetic triterpenoid compound cyano enone of methyl boswellates (CEMB) on various prostate cancer and glioma cancer cell lines. CEMB displayed concentration-dependent cytotoxic activity with submicromolar lethal dose 50% (LD50) values in 10 of 10 tumor cell lines tested. CEMB-induced cytotoxicity is accompanied by activation of downstream effector caspases (caspases 3 and 7) and by upstream initiator caspases involved in both the extrinsic (caspase 8) and intrinsic (caspase 9) apoptotic pathways. By using short interfering RNAs (siRNA), we show evidence that knockdown of caspase 8, DR4, Apaf-1, and Bid impairs CEMB-induced cell death. Similar to other proapoptotic synthetic triterpenoid compounds, CEMB-induced apoptosis involved endoplasmic reticulum stress, as shown by partial rescue of tumor cells by siRNA-mediated knockdown of expression of genes involved in the unfolded protein response such as IRE1α, PERK, and ATF6. Altogether, our results suggest that CEMB stimulates several apoptotic pathways in cancer cells, suggesting that this compound should be evaluated further as a potential agent for cancer therapy. Mol Cancer Ther; 10(9); 1635–43. ©2011 AACR.

A new total synthesis of (±)-norprezizanone

Abstract Acid catalysed rearrangement of endo 1 -methoxytricyclo[6.2.2.03,8]dodec-2-en-10-o1 8c afforded the ketone 9 which has been transformed into (±)-norprezizanone 19 thus completing a formal synthesis of (±)-zizaene. A key step in this strategy is a stereospecific 1,4-addition of a methyl group.