We describe the semi-synthesis of dihydrochalcone derivatives and their in vitro antimicrobial activities. These compounds were prepared by modifying two naturally occurring antimicrobial dihydrochalcones, erioschalcones A and B, reported by us earlier. The structures of the compounds were assigned on the basis of spectroscopic evidence and by comparing their physical and spectroscopic data with those reported in the literature. All the compounds were subjected to in vitro antimicrobial assays against a panel of pathogenic microorganisms, including gram-positive and gram-negative bacteria, and fungi. The antimicrobial efficacies of this class of compounds were established by correlating the activity profile of each compound with its structure and by comparing the activities of all the compounds with each other based on their structure. This should enable the development of other derivatives of the dihydrochalcone family that would serve as more potent antimicrobial agents against specific pathogens.

BACKGROUND:Typhoid fevers and urogenital infections continue to be serious health problems in developing countries. In our search for therapeutic agents from natural sources with potential for the treatment of typhoid fevers and urogenital infections, extract and compounds were obtained from Crinum purpurascens and tested.METHODS:Two alkaloids (4,5-ethano-9,10-methylenedioxy-7-phenanthridone or hippadine (1) and 4,5-ethano-9-hydroxy-10-methoxy-7-phenanthridone or pratorimine (2)) and one steroid (â-D-glucopyranoside of sitosterol (3)) were isolated from the CH(2)Cl(2)/MeOH (1:1) leaf extract of Crinum purpurascens and screened for antibacterial activity using both agar diffusion and broth dilution techniques.RESULTS:For the CH(2)Cl(2)/MeOH extract, the MIC values obtained were 3 mg/ml (against P. aeruginosa), 4 mg/ml (against E. coli, K. pneumoniae and S. aureus) and 6 mg/ml (against S. typhi and S. paratyphi B), whereas the MBC values varied between 7 and 12 mg/ml. For compound 1, the MIC values varied between 200 and 250 µg/ml, whereas the MBC value was 300 µg/ml against all the bacteria strains used. Compound 2 did not show any antimicrobial activity against these bacteria strains. For compound 3, the MIC values varied between 250 and 300 µg/ml, whereas the MBC values were 300 µg/ml (against S. typhi and S. paratyphi B) and > 300 µg/ml (against the other bacteria strains).CONCLUSION:These data suggest that C. purpurascens leaf extract contains antibacterial agents which could be used in the treatment of typhoid fevers and urogenital infections.

Three prenylated rotenoids, elliptol, 12-deoxo-12α-methoxyelliptone and 6-methoxy-6a,12a-dehydrodeguelin were isolated from the twigs of Millettia duchesnei, together with the known compounds, 6a,12a-dehydrodeguelin, 6-hydroxy-6a,12a-dehydrodeguelin, 6-oxo-6a,12a-dehydrodeguelin, elliptone, 12a-hydroxyelliptone and eriodictyol. Their structures were elucidated on the basis of spectral data and comparison with information reported in the literature and with authentic specimens for some known compounds. The full NMR data of 6-oxo-6a,12a-dehydrodeguelin and 6-hydroxy-6a,12a-dehydrodeguelin are reported here for the first time.

A new glyceryl derivative (Glyceryl-1-hexacosanoate) and a flavone derivative (methyletherapigenin) were isolated from the stem bark extract of Piptadenia africana, a western Cameroonian plant species. Common terpenes like sitosterol, beta-amyrin and eicosane were also isolated. These compounds were identified using physical and spectroscopic methods including mp, IR, (1)H and (13)C-NMR, DEPT, COSY, HMQC, HMBC, EI MS, HREI MS as well as some chemical transformations. The antibacterial activity of the extract, the fractions and the pure compounds is also discussed.

A new guanidine alkaloid, millaurine A (1), was isolated from the methanol extract of the seeds of Millettia laurentii. The structure of the new compound was elucidated on the basis of spectral analysis.

The genus Drimiopsis Lindl. (Hyacinthaceae) is endemic to sub-Saharan Africa, where it is represented by approximately 20 species [1]. Drimiopsis barterii Bak is the only specie of the genus which occurs in Cameroon. The plant is used by the Bamileke people of the Western province of Cameroon to treat fever. In a continuation of our search for bioactive compounds from natural source [2], a methylene chloride-methanol (1:1) extract of Drimiopsis barterii (whole plant) was investigated. Two new alkaloids (Drimiopsine A (1) and B(2)) and nine homoisoflavonids with two new structures (3, 4) were isolated.The structure of the compounds were established by MS, 1D and 2D spectroscopy including DEPT, COSY, HMQC and HMBC experiments.

Three new isoflavonoids, griffonianone F, G and H were isolated from the seeds of Millettia griffoniana, along with the known prebarbigerone, pseudobaptigenin, pseudobaptigenin methyl ether, tephrosin, dipterixine, odorantine, 7,4',5'-tetramethoxyisoflavone and isojamaicin. Their structures were assigned on the basis of spectroscopic data and chemical transformations.

Two new prenylated isoflavonoids, namely 7-methoxyebenosin and griffonianone E along with the known calopogonium isoflavone B and 7,2'-dimethoxy-4',5'-methylenedioxy isoflavone were isolated from the seeds of Millettia griffoniana. Their structures were assigned on the basis of spectroscopic data. The new compounds exhibit moderate trypanocidal and antiplasmodial activities.

Four urea derivatives were isolated from the roots of Pentadiplandra brazzeana, and their structures were elucidated by spectroscopic techniques. N-Benzyl-N'-(4-methoxybenzyl)urea (1) is a new compound, although N,N'-di-(4-methoxybenzyl)urea (2), N,N'-dibenzylurea (3), and p-methoxythiobenzaldehyde (4) are reported from a natural source for the first time.

Two guanidine alkaloids with a new skeleton, millaurine [1] and O-acetylmillaurine [2], have been isolated from the seeds of Millettia laurentii (Leguminosae). Their structures were determined from spectral studies including ir, ms, and nmr and X-ray crystallography.