Melvyn V. Sargent

Rhodomyrtone, an Antibiotic from Rhodomyrtus tomentosa

The ethyl acetate extract of the leaves of Rhodomyrtus tomentosa (Ait.) Hassk. yielded rhodomyrtone (5) [6,8-dihydroxy-2,2,4,4-tetramethyl-7-(3-methyl-1-oxobutyl)-9-(2-methylpropyl)-4,9-dihydro-1H-xanthene-1,3(2H)-di-one] which had significant activity against Escherichia coli and Staphylococcus aureus. The structural elucidation followed from spectroscopic evidence and from a single-crystal X-ray structural determination.

Preparation of methoxyphenols by baeyer–villiger oxidation of methoxybenzaldehydes

Baeyer–Villiger oxidation of methoxybenzaldehydes with m-chloroperbenzoic acid in boiling dichloromethane, followed by hydrolysis of the resultant formates, is shown to be a convenient method for the preparation of methoxyphenols.

Recent Progress in the Chemistry of Lichen Substances

Since the last major review of the chemistry of liehen substances by Huneck in 1971 (171) there has been an accelerating rate of development in this field. As with all areas of natural produet chemistry this impetus has been provided by more rapid and improved methods for detecting, isolating and purifying lichen metabolites and in the structural elucidation of these Compounds. The techniques of thin layer chromatography and high Performance liquid chromatography have provided rapid and efficient methods for the detection and purification of lichen substances and the development of 13C-n.m.r. spectroscopy and sophisticated techniques in 1H-n.m.r. spectroscopy have greatly aided structural studies.

A synthesis of αβ-unsaturated aldehydes

The synthesis and the use of 1,3-dioxan-2-ylmethyltriphenylphosphonium bromide (7) in the synthesis of αβ-unsaturated aldehydes is described.

Depsidone synthesis. Part 16. Benzophenone–grisa-3′,5′-diene-2′,3-dione–depsidone interconversion: a new theory of depsidone biosynthesis

The synthesis of a number of grisa-3′,5′-diene-2′,3-diones by oxidative coupling of substituted 2,2′-dihydroxy-4-methoxybenzophenones is described. The rearrangement of these grisadienediones to depsidones under basic, acidic, and thermal conditions is described and the mechanisms of these reactions are discussed. It is proposed that depsidone biosynthesis involves the oxidative coupling of benzophenones to grisadienediones which then rearrange to depsidones.

Synthesis and Absolute Configuration of (-)-Normalindine

The first chiral synthesis of the Strychnos and Ophiorrhiza alkaloid (−)-normalindine has been accomplished through a route starting from l-alanine methyl ester and exploiting intramolecular oxazole-olefin Diels-Alder reaction. As a result, the absolute stereochemistry of normalindine has been defined as represented by formula (−)-1.

The Alkaloids ofOphiorrhiza filistipula

Extraction of the fresh leaves of Ophiorrhiza filistipula ( Rubiaceae ) has yielded the alkaloids normalindine (2), 7-methoxycamptothecin (6) and strictosidinic acid (II). The configurations of the Strychnos alkaloids dolichantoside and isodolichantoside are revised.

Synthetic approaches to the alkaloids of the ancistrocladaceae: (–)-O-methylancistrocladine and (+)-O-methylhamatine

An asymmetric total synthesis of the naphthylisoquinoline alkaloid (–)-O-methylancistrocladine (2) is described; the synthetic method also provides routes to the atropisomer O-methylhamatine (4) and the enantiomers of these alkaloids.

Depsidone synthesis. Part 14. The total synthesis of psoromic acid: isopropyl ethers as useful phenolic protective groups

The total synthesis of 4-formyl-3-hydroxy-8-methoxy-1,9-dimethyl-11-oxo-11H-dibenzo[b,e][1,4]dioxepin-6-carboxylic acid (psoromic acid)(28), a lichen depsidone, by selective functionalization of synthetic methyl 3,8-dimethozy-1,4,9-trimethyl-11-oxo-11H-dibbnzo[b,e][1,4]dioxepin-6-carboxylate (methyl O-methylhypopsoromate)(23) and subsequent steps, is described. Attention is drawn to the use of isopropyl ethers as phenol protective groups.

A New Ring-Reduced Tetraprenyltoluquinone and a Prenylated Xanthone from Garcinia cowa

The methanolic extract of the stem bark of Garcinia cowa Roxb. (Guttiferae) yielded (2E,6E,10E)-(+)-4β-hydroxy-3-methyl-5β-(3,7,11,15-tetramethylhexadeca-2,6,10,14-tetraenyl)cyclohex-2-en-1-one 1, 4-(1,1-dimethyl-prop-2-enyl)-1,5,6-trihydroxy-3-methoxy-2-(3-methylbut-2-enyl)xanthen-9(9H)-one 2, and the known compound rubraxanthone 3. The structural conclusions are based on spectroscopic data.