Baldwin S. Mootoo

Oxazoline Mediated Routes to a Unique Amino-acid, 4-Amino-13-carboxy[2.2]paracyclophane, of Planar Chirality

Abstract Efficient syntheses leading to 4-amino-13-carboxy[2.2]paracyclophane and derivatives are described. Novel oxazolinyl[2.2]paracyclophanes are used as intermediates and the oxazolinyl and amide groups are shown to be strong ψ-geminal directing groups. Compounds with potential as catalysts have been made.

The synthesis of homochiral ligands based on (2.2)paracyclophane

Abstract A new ortho -lithiation of homochiral 4- N , N -diethylamido[2.2]paracyclophane 8 is the key to the production of a wide variety of 4,5-disubstituted homochiral ligands. ψ-Geminal bromination of 8 proceeds in high yields and the resulting bromide may be converted into a variety of 4,13-disubstituted ligands. The o- lithiation and ψ-geminal reactions can be used sequentially to give 4,5,12-trisubstituted compounds in which two liganding groups have the same geometrical relationship as in ‘Phanephos’™. Homochiral oxazolines with only planar chirality have been made, one of which has been shown to be an effective catalyst for the Heck reaction.

Briarane and asbestinane diterpenes from Briareum asbestinum

Abstract Six new diterpenes, (1–3 and 5–7), were isolated from Briareum asbestinum collected off the coast of Tobago, West Indies. Their structures were determined by a combination of 2D NMR experiments.

Sesquiterpenes from Pityrogramma calomelanos

Abstract Pterosin Z has been obtained from Pityrogramma calomelanos. A related compound calomelanolactone has also been isolated and its structure assigned from chemical, spectral, biogenetic and X-ray evidence.

Further briareolate esters and briareolides from the Caribbean gorgonian octocoral Briareum asbestinum

Abstract Eight new diterpenes were isolated from Briareum asbestinum collected off south-west Tobago. Six metabolites (4) – (9) are briareolate esters while (10) and (11) are related to the briareolides. The structures of all compounds were determined by 2D NMR spectroscopy and correlation with known compounds. The structure of compound 4 was confirmed by X-ray analysis. Compounds 4, 7, 9 and 11 showed weak activity in the brine shrimp bioassay.

Methyl briareolate, the first briarein diterpene containing a C-19 methyl ester

Abstract The structure 1 was elucidated by 2D NMR and X-ray crystal-structure analysis, which also established the relative stereochemistry. This is the first briarein diterpene containing a C-19 methyl ester.

Identification of new limonoids from Swietenia and their biological activity against insects.

BACKGROUND Natural limonoids are one group of compounds being studied for their insecticidal properties. To discover new limonoids with better activities, analogs were prepared via acylation and hydrolysis, and bioassayed. RESULTS Analogs were identified using one- and two-dimensional (COSY, HMQC and HMBC) (1) H and (13) C NMR, IR and MS. 3-O-Isovalerylswietenolide (13) and 3-O-isobutyrylswietenolide (14) showed excellent antifeedant activity, with DC(50) values of 0.19 and 0.009 mg L(-1) respectively, compared with the natural limonoid swietenolide (80.6 mg L(-1) ) against fourth-instar Spodoptera frugiperda (JE Smith) larvae. CONCLUSION This work shows that limonoid analogs prepared through semi-synthesis can be used as lead compounds for the development of new insecticides.

AN UNUSUAL ERYTHROLIDE CONTAINING A BICYCLO 9.2.1. TETRADECANE SKELETON

Abstract Erythrolide K (4), isolated from Erythropodium caribaeorum possesses an unusual bicyclo [9.2.1.] tetradecane skeleton. The structure was deduced by 2D NMR and confirmed by X-ray analysis. It was synthesised in two steps from erythrolide A (2), the first involving a thermal [1,5] sigmatropic hydrogen shift to give the intermediate (3).

7α,11β-diacetoxydihydronomilin, a new tetranortriterpenoid from cedrela mexicana

Abstract Spectroscopic and chemical evidence is presented in support of the structure of 7α,11β-diacetoxydihydronomilin (I) obtained from a benzene extract of the dehisced fruit capsules of Cedrela mexicana .

Toxicity–structure activity evaluation of limonoids from Swietenia species on Artemia salina

Context: Many plant extracts and compounds are being investigated for their cytotoxicity and hence their medicinal or therapeutic properties. Reports of toxicity studies with limonoid analogs have been sparse and have involved mainly crude extracts. In this study, individual natural limonoids have been isolated and their toxicity manipulated via semisynthesis. Objective: The lethality of limonoid analogs from Swietenia macrophylla King and Swietenia aubrevilleana Stehlé & Cusin (Meliaceae) against Artemia salina Leach was determined. Materials and methods: Four known natural limonoids were isolated from the dry ground seeds of S. macrophylla and S. aubrevilleana, modified using acylation and hydrolysis reactions and tested in A. salina lethality assays at 1–400 ppm. A 50% lethal concentration (LC50) was determined by probit analysis. Results: Higher levels of toxicity were achieved in most of the prepared analogs compared with the parent natural limonoids. The compound showing the highest toxicity with LC50 3.9 ppm was 3-O-benzoyl-3-detigloylisoswietenine (20). Other analogs with high toxicity were 6-O-benzoylswietenolide (7), 6-O-benzoylswietenine (17), and 3,6-O,O-dipropionylswietenolide (9), which showed LC50 values of 4.3, 7.5, and 28.5 ppm, respectively. Discussion and conclusions: Toxicity can be improved via semisynthesis. The compounds exhibiting high toxicity (low LC50) may be good candidates for cytotoxicity studies.