Tetrachlorovancomycin: Total Synthesis of a Designed Glycopeptide Antibiotic of Reduced Synthetic Complexity.

A technically straightforward total synthesis of a new class of vancomycin analogues of reduced synthetic complexity was developed that provided tetrachlorovancomycin (1, LLS = 15 steps, 15% overall yield) and its precursor aglycon 29 (nearly 20% overall yield). The class retains all the intricate vancomycin structural features that contribute to its target binding affinity and selectivity, maintains the antimicrobial activity of vancomycin, and achieves the simplification by an unusual addition, not removal, of benign substituents to the core structure. The modification, accomplished by addition of two aryl chloride substituents to provide 1, permitted a streamlined total synthesis of the new glycopeptide antibiotic class by removing the challenges associated with CD and DE ring system atropisomer stereochemical control. This also enabled their simultaneous and further-activated SNAr macrocyclizations that establish the tricyclic skeleton of 1. Key elements of the approach include catalyst-controlled diastereoselective formation of the AB biaryl axis of chirality (>30:1 dr), an essentially instantaneous macrolactamization of the AB ring system free of competitive epimerization (>30:1 dr), racemization free coupling of the E ring tetrapeptide, room temperature simultaneous CD and DE ring system cyclizations, a highly refined 4-step conversion of the cyclization product to the aglycon, and a protecting-group-free one-pot enzymatic glycosylation for disaccharide introduction. In addition to the antimicrobial evaluation of tetrachlorovancomycin (1), the preparation of key peripherally modified derivatives, which introduce independent and synergistic mechanisms of action, revealed their exceptional antimicrobial potency and provide the foundation for future use of this new class of synthetic glycopeptide analogues.

Divergent Total Synthesis and Characterization of Maxamycins.

A new streamlined and scaled divergent total synthesis of pocket-modified vancomycin analogs is detailed that provides a common late-stage intermediate [Ψ[C(═S)NH]Tpg4]vancomycin (LLS = 18 steps, 12% overall yield, >5 g prepared) to access both existing and future pocket modifications. Highlights of the approach include an atroposelective synthesis of [Ψ[C(═S)NH]Tpg4]vancomycin aglycon (11), a one-pot enzymatic glycosylation for direct conversion to [Ψ[C(═S)NH]Tpg4]vancomycin (12), and new powerful methods for the late-stage conversion of the embedded thioamide to amidine/aminomethylene pocket modifications. Incorporation of two peripheral modifications provides a scalable total synthesis of the maxamycins, all prepared from aglycon 11 without use of protecting groups. Thus, both existing and presently unexplored pocket-modified analogues paired with a range of peripheral modifications are accessible from this common thioamide intermediate. In addition to providing an improved synthesis of the initial member of the maxamycins, this is illustrated herein with the first synthesis and examination of maxamycins that contain the most effective of the pocket modifications (amidine) described to date combined with two additional peripheral modifications. These new amidine-based maxamycins proved to be potent, durable, and efficacious antimicrobial agents that display equipotent activity against vancomycin-sensitive and vancomycin-resistant Gram-positive organisms and act by three independent synergistic mechanisms of action. In the first such study conducted to date, one new maxamycin (21, MX-4) exhibited efficacious in vivo activity against a feared and especially challenging multidrug-resistant (MRSA) and vancomycin-resistant (VRSA) S. aureus bacterial strain (VanA VRS-2) for which vancomycin is inactive.

Improved preparative enzymatic glycosylation of vancomycin aglycon and analogues.

Modifications to the enzymatic glycosylation of vancomycin and its residue 4 thioamide analogue are detailed that significantly reduce the enzyme loading and amount of glycosyl donor needed for each glycosylation reaction, provide a streamlined synthesis and replacement for the synthetic UDP-vancosamine glycosyl donor to improve both access and storage stability, and permit a single-pot, two-step conversion of the aglycons to the fully glycosylated synthetic glycopeptides now conducted at higher concentrations. The improvements are exemplified with the two-step, one-pot glycosylation of [Ψ[C(=S)NH]Tpg4]vancomycin aglycon (92%) conducted on a 400 mg scale (2 mg to 1 g scales) and vancomycin aglycon itself (5 mg scale, 84%).

Indoline-6-Sulfonamide Inhibitors of the Bacterial Enzyme DapE.

Inhibitors of the bacterial enzyme dapE-encoded N-succinyl-L,L-diaminopimelic acid desuccinylase (DapE; EC 3.5.1.18) hold promise as antibiotics with a new mechanism of action. Herein we describe the discovery of a new series of indoline sulfonamide DapE inhibitors from a high-throughput screen and the synthesis of a series of analogs. Inhibitory potency was measured by a ninhydrin-based DapE assay recently developed by our group. Molecular docking experiments suggest active site binding with the sulfonamide acting as a zinc-binding group (ZBG).

Next-Generation Total Synthesis of Vancomycin.

A next-generation total synthesis of vancomycin aglycon is detailed that was achieved in 17 steps (longest linear sequence, LLS) from the constituent amino acid subunits with kinetically controlled diastereoselective introduction of all three elements of atropisomerism. In addition to new syntheses of three of the seven amino acid subunits, highlights of the approach include a ligand-controlled atroposelective one-pot Miyaura borylation-Suzuki coupling sequence for introduction of the AB biaryl axis of chirality (>20:1 dr), an essentially instantaneous and scalable macrolactamization of the AB ring system nearly free of competitive epimerization (>30:1 dr), and two room-temperature atroposelective intramolecular SNAr cyclizations for sequential CD (8:1 dr) and DE ring closures (14:1 dr) that benefit from both preorganization by the preformed AB ring system and subtle substituent effects. Combined with a protecting group free two-step enzymatic glycosylation of vancomycin aglycon, this provides a 19-step total synthesis of vancomycin. The approach paves the way for large-scale synthetic preparation of pocket-modified vancomycin analogues that directly address the underlying mechanism of resistance to vancomycin.

Mucinous adenocarcinoma arising in rectovaginal fistulas associated with Crohn's disease.

BACKGROUND: Crohn's disease is a chronic inflammatory disorder characterized by focal, transmural inflammation of the intestine. Gynecologic involvement, including rectovaginal fistula formation, is frequent. Case #1. A 53-year-old female with a 30-year history of Crohn's disease and numerous perirectal fistulas developed a foul smelling, purulent drainage from her rectum and a mucopurulent, bloody discharge from her vagina. A lower vaginal lesion biopsy demonstrated a low-grade mucinous adenocarcinoma. Case #2. A 42-year-old female with a 15-year history of Crohn's disease developed drainage from her vagina. Physical examination revealed an enlarging mass involving the posterior wall of the vaginal vault that connected to the anus by a fistula tract. A biopsy revealed mucinous adenocarcinoma. CONCLUSIONS: Malignant transformation of persistent rectovaginal fistulas is a potential complication of Crohn's disease.

Placental site trophoblastic tumor arising from antecedent molar pregnancy.

OBJECTIVE: Placental site trophoblastic tumor (PSTT) is a rare form of gestational trophoblastic disease. Little is known about its pathogenesis and natural history. METHODS: This report describes two cases that arose in patients with documented complete hydatidiform moles and summarizes the antecedent prenatal histories of PSTTs based on a detailed Medline literature analysis. CASES: A 28-year-old, G(2)P(2) female had a live, 12-week gestation fetus and a coexisting molar pregnancy. Her hCG levels dropped promptly from 1.5 million to 23,273 IU/ml after termination, but rose shortly thereafter together with the onset of recurrent vaginal bleeding. Curettage revealed persistent mole. Persistently elevated hCG led to hysterectomy disclosing a fundal PSTT. The second case was that of a 48-year-old, G(2) woman who presented with symptoms of preeclampsia, hyperthyroidism, and elevated hCG. Curettage yielded a complete hydatidiform mole. Although the hCG level decreased for a short period, it soon increased despite treatment with methotrexate. A second curettage revealed a PSTT. DISCUSSION: A Medline literature analysis of PSTT, which consists almost entirely of individual cases and several small series, disclosed that PSTT is preceded in 61% of cases by normal term pregnancy, 12% molar pregnancy, 9% spontaneous abortion, 8% therapeutic abortion, and 3% with ectopic pregnancy, stillbirths or preterm delivery. No information is known in 7%. This report describes two additional cases of PSTT preceded by complete molar pregnancy. CONCLUSIONS: PSTT is a well recognized, but uncommon form of gestational trophoblastic disease. Although little is known about its pathogenesis, it is preceded not uncommonly by an abnormal pregnancy, including a molar pregnancy.

Chemotherapy-induced toxic leukoencephalopathy causes a wide range of symptoms: a series of four autopsies.

We have observed an increasing number of autopsies on patients with chemotherapy-related complications. One complication is toxic leukoencephalopathy, which is due to a direct toxic effect of chemotherapeutic agents on the central nervous system white matter. Autopsies of four cases of toxic leukoencephalopathy were performed following standard protocols. The brain and spinal cord were examined routinely, and histological sections were taken for evaluation. We report here three patients with hematologic malignancies and one patient with metastatic carcinoma with chemotherapy-induced leukoencephalopathy. The first was a 56-year-old male treated with multiple chemotherapeutics for multiple myeloma. He presented with confusion and focal seizures with a rapid progression to coma and decerebrate posturing. The second was a 36-year-old male who developed mental status changes, ataxia and dysarthria following treatment for lymphoma. The third was a 16-year-old male who developed a profound peripheral and central neuropathy after chemotherapy treatment for T-cell acute lymphoblastic leukemia. The fourth was a 49-year-old female patient who was treated with multiple chemotherapeutics for Stage II breast carcinoma and subsequently developed visual acuity and field defects. The neuropathologic findings in these cases, although similar, varied in severity and distribution. The white matter was affected by severe myelin pallor, edema, and a prominent macrophage infiltrate in each of the cases. The location and extent of the central nervous system pathology correlated with the type and severity of clinical symptoms. These four cases, with their varied presenting symptoms, clinical courses, and degree of pathology, emphasize the importance of considering toxic leukoencephalopathy as an etiology of acute neurologic deterioration following high-dose chemotherapy.