Inclusion Criteria:
Part I (Single Ascending Dose) and Part II (Multiple Ascending Dose):
1. Voluntarily consents to participate in this trial and provides written informed consent before the start of any trial assessments.
2. Healthy male and female adults, 18 and 55 years of age (inclusive).
3. Participants with a body mass index (BMI) ≥ 18 and ≤ 32 kg/m2 (inclusive) and weigh a minimum of 50 kg.
4. Participants with a normal 12-lead ECG at Screening.
5. Participant has normal renal function.
6. Females participants must meet one of the following criteria:
a. Females must either be of non-childbearing potential, or if of childbearing potential, must agree to use contraceptives throughout the study period and have a negative pregnancy test at both Screening and Check-in (Day -1).
7. Males with a sexual partner who is a female of childbearing potential must be surgically sterile, or agree to use condoms with spermicide or abstain from sexual intercourse, starting from Screening until 90 days after the last dose of the trial medication.
8. Participant is willing and able to complete all trial assessments in compliance with the protocol and is able to remain in the inpatient treatment unit for the entire duration of the confinement period and return for outpatient visits.
Part III Alzheimer's Disease:
1. Participant is able to provide written informed consent prior to the performance of any trial -specific procedures.
2. Male or female participants with early Alzheimer's disease between 55 and 80 years of age (inclusive) in good health as determined by the Investigator.
3. Participants with a BMI of ≥ 18.0 and ≤ 32.0 kg/m2 (inclusive) and weigh a minimum of 50 kg.
4. Participants with a 12-lead ECG at screening which, in the opinion of the Investigator, has no abnormalities that compromise participant's safety in this study.
5. Females participants must meet one of the following criteria:
a. Females must either be of non-childbearing potential, or if of childbearing potential, must agree to use contraceptives throughout the study period and have a negative pregnancy test at both Screening and Check-in (Day -1).
6. Males with a sexual partner who is a female of childbearing potential must be surgically sterile, or agree to use condoms with spermicide or abstain from sexual intercourse, starting from Screening until 90 days after the last dose of the trial medication.
7. Participant is willing and able to complete all trial assessments in compliance with the protocol and is able to remain in the inpatient treatment unit for the entire duration of the confinement period and return for outpatient visits.
8. Participant meets the diagnostic criteria of mild cognitive impairment (MCI) of probable Alzheimer's disease consistent with National Institute On Aging - Alzheimer's Association (NIA-AA) research framework.
9. Participant with a qualifying amyloid score.
10. Participant with a Mini-Mental State Examination (MMSE) score between 20 and 28 inclusive at screening and baseline.
Exclusion Criteria:
Part I (Single Ascending Dose) and Part II (Multiple Ascending Dose):
1. History or presence of clinically significant cardiovascular, pulmonary, hepatic, renal, hematologic, gastrointestinal, endocrine, immunologic, dermatologic, neurologic, oncologic, or psychiatric disease or any other condition that, in the opinion of the Investigator, would jeopardize the safety of the participant or the validity of the trial results.
2. Participant has abnormal laboratory values detected at Screening or on clinic admission (Day -1) that suggest a clinically significant underlying disease.
3. Participant who shows evidence of suicidal ideation as assessed by the C-SSRS at screening and at Day -1 or history of suicide attempt (lifetime).
4. Participant with positive serology for Hepatitis B surface antigen (HBsAg), Hepatitis B core antibody (HBcAb), Hepatitis C Virus (HCV), or Human Immunodeficiency Virus (HIV) at Screening.
5. Participant smokes cigarettes or uses other nicotine-containing products in the past 3 months prior to Screening.
6. Participant with regular alcohol consumption within 6 months prior to the trial defined as an average weekly intake of \> 20 units for males or \> 16 units for females (8g ethanol = 1 unit).
7. Participant tests positive in the urine test for alcohol, cotinine, and/or screen for drugs of abuse at the time of screening or Day -1.
8. Participant with a history of drug abuse according to Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM V criteria or later) within the 2 years prior to study entry.
9. Participation in any clinical trial and/or recipient of investigational trial medication within 90 days prior to the first dose of 8M2D.
10. Participant with a loss of ≥ 500 mL (1 unit) of blood within 90 days prior to receiving the first dose of 8M2D.
11. In addition to the above criteria, those judged by the Investigator as not suitable for participating in this clinical trial
Part III Alzheimer's Disease:
1. Participant with history or presence of any uncontrolled systemic disease (e.g., hypertension (systolic BP ≥ 150 mmHg/diastolic BP ≥ 100 mmHg), diabetes mellitus (HbA1c ≥ 8% at the time of screening) etc.).
2. Participant with history or presence of unstable or clinically significant cardiovascular (e.g., myocardial infarction), kidney, or liver disease.
3. Participant with any active or unstable clinically significant medical or psychiatric condition as judged by the Investigator.
4. Participant who has current serious or unstable illnesses including hepatic, renal, gastroenterologic, respiratory, cardiovascular (including ischemic heart disease), endocrinologic, neurologic (other than AD), psychiatric, immunologic, or hematologic disease and other conditions that, in the Investigator's opinion, could interfere with the analyses of safety and efficacy in this trial.
5. Participant with any evidence of a condition other than AD that may affect cognition such as other dementias, stroke, brain damage, autoimmune disorders (e.g. multiple sclerosis) or infections with neurological sequelae.
6. Participant with history within the past 5 years of a primary or recurrent malignant disease with the exception of resected cutaneous squamous cell carcinoma in situ, basal cell carcinoma, cervical carcinoma in situ, or in situ prostate cancer with a normal prostate specific antigen post-resection.
7. Participant with history of intracranial hemorrhage, cerebrovascular aneurysm, or arteriovenous malformation, carotid artery occlusion, stroke, or epilepsy.
8. Participant who shows evidence of suicidal ideation as assessed by the C-SSRS at screening and at Day -1 or history of suicide attempt (lifetime).
9. Participant with positive serology for HBsAg, HBcAb, HCV, or HIV at Screening.
