N-acyloxymethyl carbamate linked prodrugs of pseudomycins are novel antifungal agents.

We describe herein the synthesis, bioconversion, antifungal activity, and preliminary toxicology evaluation of a series of N-acyloxymethyl carbamate linked triprodrugs of pseudomycins. The syntheses of these prodrugs (3-6) were achieved via simple N-acylation of PSB (1) or PSC' (2) with various prodrug linkers (7-9). As expected, upon incubation with mouse and/or human plasma, many of these prodrugs (3, 5, and 6) were converted to the parent compound within a few hours. Of particular significance, two pseudomycin triprodrugs (5 and 6) showed excellent in vivo efficacy against systemic Candidiasis without tail vein irritation being observed.

Syntheses and antifungal activities of novel 3-amido bearing pseudomycin analogues.

As a result of our core SAR effort, we discovered a large number of 3-amido pseudomycin B (PSB) analogues (e.g., 4e LY448212 and 5b LY448731) that retain good in vitro and in vivo (IP) activities against Candida and Cryptococcus without inherent tail vein irritation. Several dimethylamino termini bearing 3-amides (e.g., 5b) also exhibited improved potency against Aspergillus in vitro. When evaluated in a two-week rat toxicology study, it was found that all animals receiving 4e (up to 75 mg/kg) were found to be normal. On the basis of these observations, we are convinced that it is possible to broaden the antifungal spectrum and improve the safety profile of pseudomycin analogues at the same time.

8-Amido-Bearing pseudomycin B (PSB) analogue: novel antifungal agents.

During the course of a structure-activity relationship (SAR) study on novel depsinonapeptide pseudomycin B, we synthesized a total of 12 8-amidopseudomycin analogues via standard two-step sequence from either ZPSB 2 or AllocPSB 3. A number of these amides exhibited good in vitro antifungal activities.

The synthesis of pseudomycin C' via a novel acid promoted side-chain deacylation of pseudomycin A.

The gamma hydroxyl present in the aliphatic side chain of the natural products pseudomycin A and C' provided a unique handle for the pH dependent side-chain deacylation. Low pH reaction conditions were used to cleave the side chain with minimal degradation of the peptide core. The pseudomycin nucleus intermediate obtained from the deacylation of pseudomycin A was pivotal in the synthesis of novel side-chain analogues. A practical synthesis of a minor fermentation factor pseudomycin C' and related analogues is reported.

The synthesis and antifungal activity of N-alkylated analogs of echinocandin B.

The synthesis and biological activity of a series of N-alkylated derivatives of echinocandin B are described and compared with the N-acylated analogs. The linear, rigid geometry of the side chain that was essential to improve the antifungal potency of the N-acylated series gave similar in vitro results with the N-alkylated derivatives. However the slight structural variation forfeited all in vivo activity.

Semisynthetic chemical modification of the antifungal lipopeptide echinocandin B (ECB): structure-activity studies of the lipophilic and geometric parameters of polyarylated acyl analogs of ECB.

Echinocandin B (ECB) is a lipopeptide composed of a complex cyclic peptide acylated at the N-terminus by linoleic acid. Enzymatic deacylation of ECB provided the peptide "nucleus" as a biologically inactive substrate from which novel ECB analogs were generated by chemical reacylation at the N-terminus. Varying the acyl group revealed that the structure and physical properties of the side chain, particularly its geometry and lipophilicity, played a pivotal role in determining the antifungal potency properties of the analog. Using CLOGP values to describe and compare the lipophilicities of the side chain fragments, it was shown that values of > 3.5 were required for expression of antifungal activity. Secondly, a linearly rigid geometry of the side chain was the most effective shape in enhancing the antifungal potency. Using these parameters as a guide, a variety of novel ECB analogs were synthesized which included arylacyl groups that incorporated biphenyl, terphenyl, tetraphenyl, and arylethynyl groups. Generally the glucan synthase inhibition by these analogs correlated well with in vitro and in vivo activities and was likewise influenced by the structure of the side chain. These structural variations resulted in enhancement of antifungal activity in both in vitro and in vivo assays. Some of these analogs, including LY303366 (14a), were effective by the oral route of administration.

Correlation of cilofungin in vivo efficacy with its activity against Aspergillus fumigatus (1,3)-beta-D-glucan synthase.

(1,3)-beta-D-Glucan synthase is a cell wall synthesis enzyme that is the target of cilofungin, an antifungal agent of the lipopeptide class. Cilofungin's glucan synthase inhibitory activity, MIC, and effective dose 50% in a systemic infection mouse model tend to correlate for Candida albicans. This correlation is not seen in Aspergillus fumigatus. MICs for cilofungin against A. fumigatus were consistently > 125 micrograms/ml while the effective dose 50% in a systemic aspergillosis model was determined to be 20.6 mg/kg. To begin to understand this discrepancy, we examined the A. fumigatus glucan synthase. This cell wall enzyme was prepared and its activity was measured by [14C]-glucose incorporation from UDP-[U-14C]glucose into an acid insoluble polymer formed in the presence of alpha-amylase. Enzyme activity in crude membrane preparations was measured in the presence of several antifungal agents. Enzyme inhibition results showed that 1 microgram/ml of papulacandin B, echinochandin B, aculeacin A and cilofungin all inhibited A. fumigatus glucan synthase activity (40-71%) while 1 microgram/ml of amphotericin B, fluconazole, ketoconazole and nikkomycin did not affect enzyme activity. A correlation was therefore established between the inhibitory effect of cilofungin on the A. fumigatus glucan synthase and the effective dose 50% obtained in a systemic aspergillosis mouse model.

In vitro and in vivo anti-Candida activity and toxicology of LY121019.

LY121019 (N-p-octyloxybenzoylechinocandin B nucleus) is a semisynthetic antifungal antibiotic that possesses potent anti-Candida activity. The MIC50 and the MIC90 for both LY121019 and amphotericin B were 0.625 and 1.25 micrograms/ml, respectively. Only an 8-fold increase in the MIC against C. albicans occurred during 34-day exposure to subinhibitory concentrations indicating that LY121019 has a low potential for causing resistance development. Scanning electron microscopic studies revealed that LY121019 caused severe damage to the C. albicans cell. The ED50's for LY121019 and amphotericin B administered parenterally to mice were 7.4 and 2.5 mg/kg, respectively. Parenterally administered LY121019 at doses of 6.25 mg/kg significantly reduced the recovery of C. albicans from infected mouse kidneys. Orally administered 50 and 100 mg/kg doses of LY121019 were effective in eliminating C. albicans from the gastrointestinal tract of infected mice. Topical application of 5% LY121019 was as effective as 3% nystatin in the treatment of superficial C. albicans infections. Local administration of LY121019, nystatin, or miconazole was effective against rat vaginal candidiasis. LY121019 was administered intravenously to dogs at doses up to 100 mg/kg/day, 5 days a week for 3 months; all dogs survived. Compound related effects included a histamine-like reaction, increased serum alkaline phosphatase and SGPT, fatty vacuolization of the liver, and some tissue damage at the injection site. The no effect dose in dog was 10 mg/kg. LY121019 had no more than 1/20 the toxicity of amphotericin B in the dog.